Bash et al., 2007 自然源汞排放与模型

第37卷第5期2007年9月东南大学学报(自然科学版)J OURNAL O F SOUTHEAST UN I V ERS I TY (Natural S ci en ce Ed iti on)V o l 37No 5Sep.t 2007燃煤电厂汞排放特性实验研究杨立国 段钰锋 杨祥花 江贻满 王运军 赵长遂(东南大学洁净煤发电及燃烧技术教育部重点实验室,南京210096)摘要:选取了我国6个比较有代表性的燃煤电厂,采用美国EP A 推荐使用的OH 方法,对其入炉煤、底渣、飞灰、脱硫产物及烟气进行了取样分析,并针对系统汞的排放进行了平衡计算.测量了不同电厂的除尘器灰的含碳量,以分析其对飞灰中汞富集因子的影响.实验结果表明:在所测的6个燃煤电厂中,底渣排汞量不到总汞的1%,煤中的汞在燃烧区域以后绝大部分以气态和飞灰吸附态的形式排放,并随着机组容量的增大,气态汞的排放比例也有所增大.飞灰中的残碳对气态汞向飞灰的富集有促进作用,飞灰的含碳量与飞灰中汞的富集因子呈正相关关系.烟气中的氯元素可以提高可溶性二价汞的含量.实验研究表明,循环流化床燃烧方式可以极大地减少气态汞的排放量,其机理还有待于进一步研究.关键词:燃煤电站;汞排放;汞平衡;飞灰中图分类号:TK224 9+3 文献标识码:A 文章编号:1001-0505(2007)05 0817 05M ercury e m ission characteristics fro m coal fire d po wer pl antsY ang L iguo D uan Y ufeng Y ang X ianghua Jiang Y i m an W ang Y un jun Zhao C hangsui(Key Labo rat o ry o f C l ean C oalPow er G eneration and C om bu sti on T echno l ogy o fM i n istry of Education,S out h eastUn iversity ,N an ji ng 210096,C h i na)Abst ract :To eva l u ate the m ercury e m issi o ns ,and to co m prehend and com pare t h e s pec iati o n characteristics o f m ercury i n differ ent pow er plants ,six representa ti v e coa l fired po w er plants w ere selected ,of w hich t h ere w ere five pul v erized coal bo ilers and one circu l a ti n g flui d ized bed bo iler ,w ho se capac i ti e s ranged fro m 50MW to 600MW w ith different fl u e gas cleaning up dev i c es such as electro static precipitator (ESP),fabric filter (FF)and fl u e g as desulfuri z ation (FGD ).Sa m p les o f feed i n g coa,l bo ttom ash ,fl y ash ,desulfurization sorbent and flue gasw ere taken at the inlet and outl e t of po ll u tion contr o l dev ices fro m the si x differen t coa l fir ed pow er p lants .The resu lts of m ercury e m issi o n and m ercury balance s how that the m ercury speciation distri b uti o n changes g r eatly dependi n g on coal types ,co m busti o n bo ilers and d ifferent a ir po llution contro l dev i c es (APCD ).The fly ash exerts dif ferent i n fl u ence s onm ercur y adso r ption ,and the chlorine content i n flue gas can convertm o re ox i d ized m ercury .It is show n that circulating flui d ized bed com busti o n (CFBC )can decrease the to tal g aseous m ercury e m issi o n ,how ever the m echan is m needs to be further i n v esti g a ted .K ey w ords :co al fired pow er plan;t m ercury e m issi o n;m ercury ba l a nce ;fl y ash 收稿日期:2007 01 08.基金项目:国家重点基础研究发展计划(973计划)资助项目(2002CB 211604,2006CB 200301)、985教育部 振兴行动计划 一期联合资助项目.作者简介:杨立国(1978!),男,博士生;段钰锋(联系人),男,博士,教授,博士生导师,yfduan@seu .汞是一种神经毒物,而且是一种生物积累物质,对人类健康威胁很大.研究表明[1],燃煤汞排放是主要的人为大气汞排放源.根据Chu 等[2]研究,目前全球人为源汞散发量约4000t/a ,1995年中国燃煤大气排汞量为213 8,t 约占总量的5%.中国一次性能源以煤炭为主,1995年我国煤炭消耗量为13 8亿,t 居世界第一位[3],中国燃煤大气汞排放量自1978年至1995年年平均增长速度为4 8%,全国累积汞排放量为2493 8t [4].煤炭利用过程中,大量的汞被释放到大气中,对人类健康造成直接或潜在的危害.本文采用美国国家环保署(EP A )标准燃煤电厂汞取样分析方法对选取的我国6个燃煤电厂进行了系统全面的取样分析测试研究工作,获取了我国现阶段燃煤电站配置条件下汞排放特性的实验数据,掌握了目前我国部分燃煤电厂汞排放现状和规律,为将来我国燃煤电厂汞排放控制政策的制定提供了有益的参考.1 实验系统本文选取了我国6个比较有代表性的燃煤电厂锅炉系统进行实验研究,各个电厂系统配置如表1所示.实验对电厂的入炉煤样、底渣、预除尘器灰、除尘器灰、脱硫产物和烟气等进行了取样分析研究.固态产物的取样与烟气采样同时进行.取样点的布置如图1所示.表1 6个燃煤电厂锅炉容量和污染物控制装置电厂地点锅炉类型机组容量/MW设计煤种污染物控制1#北京W型火焰、飞灰复燃、液态排渣直流炉220神华煤静电除尘器2#内蒙古四角切圆燃烧方式煤粉炉200准格尔烟煤布袋除尘器3#内蒙古单炉膛 型煤粉炉50准格尔烟煤布袋除尘器4#内蒙古直流式燃烧器四角切圆燃烧方式、固态排渣煤粉炉600准格尔烟煤静电除尘器5#河北四角切圆方式、单炉膛 型露天布置、固态排渣煤粉炉600神华煤静电除尘器+湿法脱硫6#江苏固态排渣、超高压循环流化床蒸汽锅炉135混和煤种静电除尘器图1 电场飞灰取样点示意图烟气取样采用美国环保署(EPA)和能源部(DOE)等机构推荐的汞测试分析的标准方法OH 方法,如图2所示,其流程为:采样系统从烟气流中等速取样,取样管线的温度维持在120∀以上.取样系统主要由石英取样管及加热装置、过滤器(玻璃纤维滤筒)、吸收瓶(置于冰浴中)、流量计、真空泵等组成.颗粒态汞由位于取样枪前端的玻璃纤维滤筒捕获,氧化态汞由3个盛有KC l溶液的吸收瓶收集,元素汞由1个装有HNO3+H2O2溶液和3个装有KM nO4+H2SO4溶液的吸收瓶收集,最后由盛有干燥剂的吸收瓶吸收烟气中的水分.取样结束后,进行样品的恢复和消解;所有消解过的样品称重后立即送入全自动测汞仪H ydra AA进行检测.固态产物中汞含量的测定采用全自动汞测量仪DM A80来进行,DM A80固液相自动测汞仪将样品的加热过程和原子吸收光谱检测装置集于一身,能直接测定固体或液体中的总汞含量.图2 OH方法烟气汞等速取样系统简图2 结果与分析通过对6个燃煤电厂全负荷运行条件下的煤、底渣、飞灰、烟气(及脱硫产物)汞浓度数据和运行工况的计算分析,可以得到电厂在全负荷运行工况下的汞平衡,如表2和图3所示.表2 不同电厂不同形态汞的排放量g/h电厂煤中汞底渣中汞除尘器前不同形态汞排放量Hg0H g2+H g P除尘器脱除汞除尘器后不同形态汞排放量Hg0H g2+H g PW FGD脱除汞脱硫装置后不同形态汞排放量Hg0Hg2+H g P1#0 810 000 720 070 020 040 570 050 00!!!!2#26 40 0410 812 00 720 455 7017 60 00!!!!3#8 700 010 862 552 804 400 181 170 15!!!!4#69 60 2886 713 20 372 1236 530 90 00!!!!5#10 00 757 990 310 030 049 541 230 000 869 740 410 00 6#2 720 130 020 001 311 970 010 000 02!!!!2.1 汞平衡及排放因子煤燃烧后,汞被再分配到粉煤灰、炉渣和烟气中,通过实验研究,发现所测试的6个电厂中,进入飞灰中的汞占3 3%~99%,其中江苏某电厂135818东南大学学报(自然科学版) 第37卷图3 6个燃煤电厂的汞平衡ＭＷ的循环流化床锅炉高达99%.进入炉渣中的汞占0 00%~0 97%.排入大气中的汞占0 96%~90 9%,135MW 的循环流化床锅炉只有0 96%.汞排放因子(EF)表示燃煤电厂烟气中的汞排放到大气中的排放量,即人们通常所说的最终向大气排放的汞强度.根据1996年美国DOE 对9个电厂的汞浓度现场测试,结果显示其排放因子为0 82~9.46m g /G J [5],本文汞排放因子计算参照此文献,但使用了国际单位,具体定义如下:E f =m Hg GQ式中,E f 为汞排放因子;m Hg 为排放到大气中的汞量;G 为给煤量;Q 为煤的低位发热量.图4 燃煤电厂不同形态汞排放比例由图4可以看出,不同电厂燃煤汞的排放因子有很大差别,这主要是由煤质特性(主要是汞含量和低位发热量)决定的.而不同电厂又由于燃烧设备、运行工况以及污染物控制设备的不同,导致燃煤烟气汞排放因子有所不同.1#,2#,4#和5#电厂表明在全负荷运行条件下,现有的污染物控制装置对气态汞排放的控制没有多大作用,煤中汞几乎全部以不同气态汞形态排入大气;3#和6#电厂由于机组容量较低和循环流化床燃烧方式,导致飞灰含碳量较高(见表3),从而使得煤中汞绝大多数以固态产物形式得以脱除,只有极小一部分被排入大气.表3 各个电厂飞灰含碳量电厂取样编号除尘器(ESP 或FF)灰含碳量%一电场二电场三电场四电场1#507212 922 632 592 57507241 432 043 833 03507252 853 153 192 54507262 822 082 532 242#50803A0 9250803B 0 92508041 333#50807A2 8750807B3 18508092 594#508131 340 70 7950814A 0 90 920 930 8350814B 0 826#50912A 11 29 8950912B 12 0310 *******C1110 34图5所示为电厂汞以不同形态的排放比例按电厂机组容量的变化情况.说明汞的排放形式与电厂机组容量有很大关系.从本实验所得结果来看,较低的锅炉容量和循环流化床燃烧方式可以比较有效地控制燃煤电厂汞的大气排放.CFB 对汞的高脱除效率也被EP A 的现场测试所报道.美国EPA 对84台锅炉进行了现场测试工作,其中共选取了5台带FF 的CFB 锅炉,发现这种燃烧方式具有从66%~99%的汞脱除效率[6],平均值为86%.图5 燃煤电厂不同形态汞排放比例2 2 飞灰含碳量对汞排放特性的影响近年来,国内外学者对汞的吸附脱除做了大量的研究,取得了一系列成果,普遍认为燃煤飞灰能吸附烟气中的汞[7-9].飞灰作为汞的一种廉价吸附剂正日益受到人们的重视.表3列出了不同电厂除尘器灰的含碳量.图6所示为不同电厂的除尘器电场灰中汞的富集因子I k 随飞灰含碳量的变化趋势.由图6可以看出,同一电厂的不同除尘器电场819第5期杨立国,等:燃煤电厂汞排放特性实验研究灰中汞的富集因子随着含碳量的增大而增大;不同电厂的除尘器灰其汞的富集因子基本上也是与含碳量呈正相关性,只不过受烟气成分(主要是C l 元素)等其他因素的影响而有所偏离.图6 电场灰中汞的富集因子随飞灰含碳量的变化如图7所示,可以从飞灰含碳量来解释不同机组容量对汞排放特性的影响:锅炉容量越小,炭颗粒在炉内的停留时间越短,则飞灰中含碳量越高,导致飞灰中汞的富集因子增大,从而汞的气态排放量越小;反之则越大.循环流化床锅炉飞灰含碳量最高,所以汞的富集因子较高.图7 除尘器灰的含碳量随电厂锅炉容量及锅型变化2.3 烟气成分对燃煤电厂汞形态分布的影响规律文献[10]研究了20~900∀范围内燃煤烟气中各气体成分的化学反应性质,发现H g 0(g)与HC l (g),C l 2(g)可迅速反应.以下为H g 0(g)与烟气中C l 2和HC l 可能发生的反应:H g 0(g )+C l 2(g)#H gC l 2(s ,g)H g 0(g)+C l 2(g)#H g 2C l 2(s)H g 0(g)+HC l (g)#H gC l 2(s ,g)+H 2(g)H g(g)+HC l (g)+O 2(g)#H gC l 2(s)+H 2O (g)H a ll 等[10]同时还发现汞-氯系统中C l 2(g)的活性更大.本文通过对6个燃煤电站汞排放特性和烟气成分的分析研究,总结了几个影响烟气中气态二价汞H g 2+(g)含量的因素,如图8和图9所示.图8 氧化汞所占烟气总汞百分比随HC l 浓度的变化图9 氧化汞所占烟气总汞百分比随C l 2浓度的变化可以看出,烟气中二价汞比例与烟气中C l 的含量基本上是正相关性的.烟气中的气态二价汞H g 2+(g)易溶于水,可以被湿法脱硫装置(W FGD )脱除,因此提高烟气中气态二价汞H g 2+(g)的含量,是一种汞排放控制的有效手段.这表明烟气中的C l 有利于燃煤电厂气态汞排放的控制.3 结论1)对6个燃煤电厂的煤、底渣、飞灰、烟气(及脱硫产物)进行了取样分析,并针对系统汞的排放进行了平衡计算,得到了燃煤电站汞的富集规律和排放特性.2)现阶段还缺乏基于实验数据的对我国燃煤电厂汞排放总量和排放特性的研究.本文所选取的6个有代表性的燃煤电厂的实验研究表明,不同装机容量,燃用不同煤种的电厂其汞排放总量有很大差异,而我国不同煤种,甚至相同煤种的不同煤层之间汞含量的差距很大,这给估算我国燃煤电厂汞排放总量造成困难.3)不同的煤种、机组容量和污染物控制装置造成燃煤电厂汞排放特性的不同,随着机组容量的增大,汞的大气排放量有增大的趋势.4)就本文的研究来看,循环流化床锅炉可以有效地控制汞向大气的排放;烟气中的氯元素可以提高烟气中可溶性二价汞的含量.5)飞灰中的残碳可以增强飞灰对气态汞的吸附作用.不同的燃烧工况和燃烧设备会造成飞灰的820东南大学学报(自然科学版) 第37卷物理化学性质的不同,这导致烟气中颗粒态汞含量差异极大,并直接导致汞向大气中排放量的不同,飞灰对烟气中汞的吸附机理和吸附脱除能力值得进一步研究分析和开发利用.本实验工作是与清华大学热能工程系禚玉群副研究员、陈雷硕士、张亮博士研究生等共同努力工作完成的,在此表示感谢.参考文献(References)[1]M e ij R.T he fa t e o f m ercury i n coa l fired pow er p l antsand t he i nf l uence o f w e t f l ue ga s de s u l phurizati on[J].W a ter,A ir and So il P o lluti on,1991,56(4):21-23. [2]Chu P,Po rcell a D B.M e rcury stack e m issi on s from U SAelectr i c utility pow er plants[J].W a te r,A ir and So il P o ll uti o n,1995,80(1/2/3/4):135-144.[3]王起超,马如龙.煤及其灰渣中的汞[J].中国环境科学,1997,17(1):76-79.W ang Q i chao,M a R ulong.T he m e rcury i n co al and itsci nder[J].C hi na Env iron m enta l Science,1997,17(1):76-79.(i n C hine se)[4]王起超,沈文国,麻壮伟.中国燃煤汞排放量估算[J].中国环境科学,1999,19(4):318-321.W ang Q ichao,ShenW eng uo,M a Z huangw e.i T he esti m ati on o f m ercury em ission from co al com bustion o f Ch i na[J].Ch i na Environ m enta l Science,1999,19(4):318-321.(i n Ch i nese)[5]EERC.A com prehensi v e asse ss m en t o f to x ic em issionsfrom coa l f i red pow er p l ants:phase∃,results from t he U.S.D epart m ent o f Energy S t udy[R].N o rth D ako t a:G rand Fo rks,1996.[6]John H,P av lish E A S,M i chae lD M ann,et a.l Status rev i ew o f m ercury con tro l op tions fo r co a l fired pow er plants[J].Fue l P ro cessing Techno l o gy,2003,82(2/3):89-165.[7]A uro ra R ube,l R o dney A ndrew s,R o l ando G onzalez,eta.l A dsorpti on o f H g and NO x o n co a l by products[J].Fue l,2005,84(7/8):911-966.[8]G ran ite E J,P enn line H W,Ha rg is R A.N ov e l so rben tsfor m ercury re m ov al from flue gas[J].Ind&Eng Che m R es,2000,39(4):1020-1029.[9]H assett D J,Ey l ands K E.M ercury capture on co a l fl yash[J].Fuel,1999,78(2):243-248.[10]H a ll B,Schag er P,L i ndqv ist O.Che m i ca l reacti o ns o fm e rcury on com bustion flue ga ses[J].W a ter,A ir andSo il P o ll uti o n,1991,56(4):3-14.821第5期杨立国,等:燃煤电厂汞排放特性实验研究。

水体汞污染的危害与防治摘要：由于特殊的物理化学性质和强的毒性,汞已经成为全球关注的污染物。

本文对目前水体汞污染的来源及现状，汞污染对人体的伤害，以及部分汞污染治理方法进行了解析。

关键词：汞污染来源危害治理1.汞污染1.1 什么是汞？汞俗称水银,常温下是银白色的液体，是室温下唯一的液态金属，有流动性。

在自然界中主要以金属汞、无机汞和有机汞化合物的形式存在。

汞易蒸发,汞,汞蒸气,及汞的化合物均有剧毒!汞的用途非常广泛，但汞也严重的污染着人类的生活环境，威胁人类健康。

因此，认识和防治汞污染是非常必要的。

1.2 水体汞污染的来源汞的排放来自于自然源和人为源两个部分，自然源包括：火山活动、自然风化、土壤排放和植被释放等，人为源排放指的是因人类活动引起的汞排放，包括汞的使用、物质当中含有汞杂质以及废物处理引起的汞排放三大类。

水体中汞的来源，一是由于人们对汞处理应用不当，造成局部或小范围水体汞含量超标；二是由于汞化工工厂对废水未经处理直接排放到河流中；三是由于化石燃料燃烧向大气中排放了大量气态和颗粒态的汞，一部分通过降雨等形式进入水体中，另一部分通过固、液、气三态循环或化学反应融入水体。

2.汞污染对人体的危害汞是环境中毒性最强的重金属元素之一。

水体中的元素汞和无机汞可被微生物转化为甲基汞，水生生物摄入甲基汞，可以在体内积累，并通过食物链不断富集（生物放大）。

受汞污染水体中的鱼，体内甲基汞浓度可比水中高上万倍，通过食物链使人体暴露量增加，毒性效应增强。

因此，处于食物链顶端的人类，是汞污染的最大受害者。

微量的汞在人体内不致引起危害，可经尿、粪和汗液等途径排出体外，如数量过多，即可损害人体健康。

汞和汞盐都是危险的有毒物质，严重的汞盐中毒可以破坏人体内脏的机能，常常表现为呕吐现象，牙床肿胀，发生齿龈炎症，心脏机能衰退。

汞毒可分为金属汞、无机汞和有机汞三种。

金属汞和无机汞损伤肝脏和肾脏，但一般不在身体内长时间停留而形成积累性中毒。

酱油作业指‎导书酱油加工工‎艺分为：黄豆、麦仁→分别浸泡→分别蒸煮→出锅→降温→接种→分别入曲罐‎△→保温→分别制曲→翻曲→通风培养→成曲→混合入曲→加入盐水→保温发酵→淋浇→浸出→配兑→灭菌→灌装→成品→入库△1. 浸泡将黄豆和麦‎仁分别放入‎浸泡罐中，黄豆浸泡1‎8小时、麦仁浸泡4‎小时，然后用笊篱‎捞出备用。

2. 蒸煮将浸泡好的‎黄豆、麦仁分别放‎入蒸笼中；每锅加入黄‎豆与麦仁量‎分别为75‎0千克；蒸煮温度控‎制在100‎℃左右；蒸煮时间为‎45分钟。

3. 接种将蒸煮好的‎黄豆和麦仁‎移入接种床‎中，冷却到40‎℃，接入菌种，接种量为0‎.3-0.5﹪，翻拌均匀。

4. 制曲将接好种的‎曲料，移入制曲罐‎中，静止培养8‎小时，品温在30‎-32℃。

再通风培养‎至15小时‎后，翻曲。

翻曲后，再通风10‎-12小时，停风，堆积升温2‎小时后，此时，料温在50‎℃，出曲。

5. 发酵，将成曲移入‎发酵罐中，将曲块破碎‎，加入10-12Be盐‎水，盐水温度是‎50-55℃，盐水和料得‎比例2:1，发酵温度控‎制在40-45℃，周期40天‎。

6. 浸出将发酵好的‎酱醅加入8‎0℃以上的热水‎，浸泡8小时‎，放油。

再浸泡2小‎时，二次放油。

7.配兑将生油按不‎同的质量进‎行配兑.加入山梨酸‎钾，加入量为0‎.8‰以下.8.将需要灭菌‎的酱油用泵‎打入灭菌锅‎中，然后将酱油‎温度加热至‎80—85℃；待温度达到‎后开泵将酱‎油打入成品‎灌中，将成品罐中‎的酱油迅速‎降温至常温‎下备用。

9.灌装：将灭菌好的‎酱油打入成‎品罐中，然后经灌装‎机灌装、贴标、检验、封箱。

10.成品入库：将包装好的‎酱油经包装‎车间运至成‎品库中，成品库要求‎离开地、墙摆放整齐‎，规格明示。

矿床地质MINERAL DEPOSITS2024年2月February ，2024第43卷第1期43（1）：215~222*本文得到国家自然科学基金项目（编号：42122012、92062219）和国家重点研发计划项目（编号：2023YFC2906800）联合资助第一作者简介赵刚，男，1997年生，博士研究生，地质学专业。

Email:***************通讯作者翟德高，男，1985年生，教授，主要从事低温热液成矿系统研究。

Email:***************.cn 收稿日期2023-12-11；改回日期2024-01-30。

秦思婷编辑。

汞是自然界中常温常压下唯一以多形态（气、液、固）和多价态（0、+1、+2）存在的金属元素，汞也是自然界唯一同时存在显著同位素质量分馏和非质量分馏的金属元素。

汞具有许多独特的、有用的物理化学性质，被广泛应用于化学、医药、冶金、电器仪器、军事以及其他精密高科技领域。

然而汞也伴随着黑暗与危险，它是毒性最强的重金属污染物之一，经生物累积可对人体健康和环境造成显著不利影响。

汞在各类地质储库中的分布并不均匀，低需求、高污染以及独特的地球化学性质制约了有关汞矿床的研究。

2017年《关于汞的水俣公约》正式生效，这一国际公约针对汞提出全面管控要求，作为汞的生产、使用和排放大国，中国已出台一系列控制汞排放和减少汞污染的积极举措，充分展现了大国担当。

1汞的发现及性质1.1汞的发现简史汞俗称水银，英文单词与水星（Mercury ）相同，它们都源于罗马神话以速度和流动性著名的信使神——墨丘利（Mercury ）。

现代化学中，汞的符号是Hg ，它来自人造拉丁词hydrargyrum ，其词根来自希腊语，这个词的2个词根分别表示“水”（hydro ）和“银”（argyros ）。

古代的西班牙人将汞称为“快银”（quicksilver ），也就是活动之银。

汞及其主要矿物辰砂（也称朱砂、丹砂）很早就被人类认识并加以利用，在古文明的遗址中经常可以发现汞的痕迹。

摘要：汞在自然界的丰度不大, 但分布很广。

早在几千年前, 人类就知道汞有毒, 而且毒性很强。

而不是人及生物体必须的元素反而能和人及生物体内的高分子形成稳定的几乎不离解的配合物, 很难排是体外, 对人和物体进成严重危害。

到19 世纪以后, 随着工业的发展, 汞的用途越来越广。

结果大量汞进入人类活动的环境。

目前全世界每年开采应用的汞量约一万吨以上, 其中有些最终都以“三废”的形式进入环境。

一个年产十几万吨乙醛工厂就有5 0 0 一1 5 0 0 kg汞经废水流入江河。

因此, 防治汞污染是一项重要而艰巨的任务。

[1]正文1 汞汞俗称“水银”，是地壳中相当稀少的一种元素，极少数的汞在自然中以纯金属的状态存在，是唯一的液体金属。

朱砂、氯硫汞矿、硫锑汞矿和其它一些与朱砂的矿物是汞最常见的矿藏。

大约世界上的汞来自西班牙和意大利其他主要地是斯洛维尼亚、俄罗斯和北美。

朱砂在流动的空气中加热后汞可以还原，温度降低后汞凝结，这是生产汞的最主要方式。

2 汞的特性汞是一种化学元素，俗称水银汞亦可写作。

它的化学符号是，原子序数是。

它是一种很重、银白色的液态过渡金属。

比重熔点℃沸点℃。

水银在常温下具有可蒸发、吸附性强、容易被生物体吸收等特性，其蒸气无色无味，比空气重七倍。

汞的导热性能差，而导电性能良好。

汞有一种独特的性质，它很容易与几乎所有的普通金属形成合金，包括金和银，但不包括铁。

它可以溶解多种金属如金、银、钾、钠、锌等。

溶解以后便组成了汞和这些金属的合金，被称为汞齐，如金汞齐、钠汞齐。

商业上汞的交易一般以一个“烧瓶”的容量作单位，约重公斤。

汞是一种可以在生物体内积累的毒物，无机汞和有机汞均能在生物体内积累，通过生物体内积累和食物链能大大提高汞的危害性。

环境中任何形式的汞均可在一定条件下转化为剧毒的甲基汞，甲基汞有一甲基汞、碘化甲基汞和二甲基汞。

[2]3．汞污染来源汞污染主要来自汞矿开采、冶炼、氯碱生产、造纸、塑料等的工业三废中、及含汞农药与医药等。

An approach towards an estimate of the impact of forest management and climate change on the European forestsector carbon budget:Germany as a case studyTimo Karjalainen a,*,Ari Pussinen a ,Jari Liski a,b ,Gert-Jan Nabuurs a,c ,Markus Erhard d ,Thies Eggers a,e ,Michael Sonntag f ,G.M.J.Mohren gaEuropean Forest Institute,Torikatu 34,80100Joensuu,FinlandbDepartment of Forest Ecology,University of Helsinki,P .O.Box 24,FIN-00014Helsinki,Finland cALTERRA,Green World Research (the former IBN-DLO),Wageningen University and Research Centre,P .O.Box 23,NL 6700AA Wageningen,The NetherlandsdPotsdam Institute for Climate Impact Research,P .O.Box 601203,D-14412Potsdam,Germany eGeorg-August University of Go¨ttingen,Faculty of Forest Sciences and Forest Ecology,Institute of Forest Management and Yield Science,Bu¨sgenweg 5,D-37077Go ¨ttingen,Germany fCenter for Environmental Systems Research,University Gh Kassel,Kurt-Wolters Str.3,D-34109Kassel,GermanygForest Ecology and Forest Management Group,Department of Environmental Sciences,Wageningen University and Research Centre,P .O.Box 342,NL-6700AH Wageningen,The NetherlandsAbstractThe increasing concentration of greenhouse gases in the atmosphere and the consequent warming of the Earth’s surface presents a threat to the environment and economic development.This paper discusses how regional level impacts of transient climate change on forest growth are assessed with process-based models and how these responses are then scaled up to country and European level using national forest inventory data in combination with the European forest information scenario (EFISCEN)model.Stem wood volume and increment in the EFISCEN model is converted to whole tree biomass based on information from process-based models.Calculation of carbon in soil and in wood products is included in this approach.A preliminary carbon budget under current and changing climatic conditions,with current management regime for Germany,is presented and discussed.Although carbon stocks in trees,soil and products are increasing,we found that the German forest sector can sustain a carbon sink until 2050,but the sink gradually becomes smaller,declining from 1.7Mg C/ha per year in 1995to 0.7Mg C/ha per year in 2050.This is due to ageing of forests,as sink activity in older forests is smaller than in younger forests.The sink activity in the soil increased slightly,but rate of storage in trees decreased more.Under changing climatic conditions,both carbon stock and sink activity in trees and soil were larger than under current climatic conditions.International processes,such as the United Nations Framework Convention on Climate Change (UNFCCC)and The Kyoto Protocol require integrated assessments of the role of forests and forestry on mitigation of climate change,but there is also a need for assessments of the impacts of climate change on forests.Research can provide information for decision-makers regarding the functioning of the system,potential risks and uncertainties.The upscaling approach described in this paper will be used later to investigate the impacts of selected forest management scenarios,under current and changing climatic conditions,on the forestry carbon budgets of 27European countries.#2002Elsevier Science B.V .All rights reserved.Keywords:Carbon budget;Climate change;Forest sector;Integrated assessment;ScenariomodellingForest Ecology and Management 162(2002)87–1031.IntroductionForests and global climate are connected through the global carbon cycle.Globally terrestrial ecosys-tems exchange large amounts of carbon with the atmosphere,but netfluxes are much smaller as Steffen et al.(1998)have demonstrated:120Pg C per year gross primary production(GPP),60Pg C per year short-term carbon uptake as net primary production (NPP¼GPP minus plant respiration),10Pg C per year medium-term carbon uptake as net ecosystem production(NEP¼NPP minus decomposition)and 0–2Pg C per year long-term carbon uptake as net biome production(NBP¼NEP minus disturbances). Dixon et al.(1994)have reported that forests in Europe constitute a sink of0.09–0.12Pg C per year while forests globally would be a source of0.5–1.3Pg C per year mainly because of deforestation in the tropics.Why forests in Europe are a sink of carbon?Has the area of forest increased or has the biomass in forest increased?Kuusela’s study(1994)shows that the area of exploitable forests in Europe has actually changed very little since1950,but that the growing stock has increased over40%at the same time.Fellings have been fairly stable but increment has increased and therefore,the growing stock has increased,too. Increasing difference between the increment and fell-ings have resulted in net accumulation of carbon in the tree biomass as Kauppi et al.(1992)and Dixon et al. (1994)studies showed.International conventions,such as the United Nations Framework Convention on Climate Change(UNFCCC)and The Kyoto Protocol require information on the future development of forest resources and their carbon budget,as well as on how climate change is likely to influence these resources. The aim of this paper is to describe how regional level responses of climate change on forest growth can be scaled up to national and European levels using forest inventory data together with a large-scale sce-nario model.Subsequently,it is shown how the con-sequences for carbon budgets can be assessed in such an approach.First,we describe the method;next,we present a preliminary carbon budget for Germany under current and changing climatic conditions and current forest management for the period1990–2050.This has been based on work in a European Union funded project ‘‘Long-Term Regional Effects of Climate Change on European Forests:Impact Assessment and Conse-quences for Carbon Budgets’’which investigated the impacts of climate change on the long-term growth and development of European forests.2.Methodsrge-scale scenario modelThe European forest information scenario(EFIS-CEN)model is a forest resource model,suitable for large-scale(>10000ha)and long-term(20–70years) analysis for future development of forest resources in Europe.Projections with EFISCEN model provide insight in increment,growing stock,age class distri-bution and actual felling per tree species.The core of the forest growth simulator of the EFISCEN model was originally developed at the Swedish University of Agricultural Sciences(Sallna¨s,1990)and was used to study the impact of air pollution on European forests (Nilsson et al.,1992).The model has been further improved and the current version(EFISCEN2.0)is described in Pussinen et al.(2001).Using the model, new analyses have been made of the development of forest resources in Europe in general and of the Leningrad region more in particular(Nabuurs et al., 1996,1998;Pa¨ivinen et al.,1999).A comparison with historical data for Finland was published by Nabuurs et al.(2000).National forest inventory data are used as input for the EFISCEN model,including area,volume and net annual increment by age classes(Fig.1).In order to define a management regime,assumptions for thinning andfinal felling are included. Improvements of the model include incorporation of transient changes in forest growth due to climate change,as well as conversion of stem wood volumes to whole tree biomass and carbon stocks.The model has been extended by including litter production,as well as dynamic sub-models for soil carbon and wood rmation from process-based models can be used to convert stem wood volumes to whole tree biomass and to produce litter.Current forest growth in the model can be modified based on process-based model assessments of climate change impacts on forest growth.A carbon book-keeping approach has been included to calculate carbon budgets of forests and wood products.88T.Karjalainen et al./Forest Ecology and Management162(2002)87–1032.2.State and growth of forestsThe current state of the forest is represented as an area distribution over age and volume classes in volume –age matrixes (Fig.2).Growth is included as area changes to higher volume classes and ageing of forests is incorpo-rated as a function of time up to the point of clearcut.Transition from a clearcut area to regenerated area is through a bare-forest-land class.Fellings are speci fied for the whole country for each species group for each time period.The basic input data include forest area,growing stock and increment by age classes,i.e.the data gathered in the national forest inventories.A separate matrix is set up for each forest type provided in the inventory data.Forest types are distinguished by region,owner class,site class and tree species,depending on the aggregation level of the provided data.The projection of the growth in the model is based on growth functions that are calibrated based on the inventory data.The projections carried out with the EFISCEN model pro-vide insight in increment,growing stock,age class distribution,actual felling per tree species and region.2.3.Biomass and litter productionBased on the calculated standing stem wood volumes in the EFISCEN model,the biomass of branches,coarseroots,fine roots and foliage are calculated.For this calculation,the model needs dry wood basic density and biomass distribution by age class.The biomass distributions are de fined for each region and tree spe-cies.Process models provide biomass distributions that can be used for biomass calculations in the EFISCEN model.Conversion of biomass to carbon is based on the assumption of 50%carbon content of dry matter.Each year a proportion of the stems,branches,roots and leaves of the trees die,resulting in litter produc-tion.Both biomass distribution and litter production can be changed in time due to changes in environ-mental conditions,such as climate change.Thinning and final felling operations result in additional litter production and the amount of produced litter depends on the harvest level in the region and felling method (which biomass components are left in the forest).In the current upscaling approach,both biomass dis-tribution and litter production are based on process model outputs.2.4.SoilThe EFISCEN model contains a dynamic soil car-bon sub-model that calculates the amount of carbon in soil.The sub-model consists of three litter compart-ments describing physical fractionation of litterandFig.1.Outline of the EFISCEN model.T.Karjalainen et al./Forest Ecology and Management 162(2002)87–10389five compartments describing microbiological decom-position in soil (Fig.3).Of the litter compartments,one is for stem litter,one for branch and coarse root litter and one for foliage and fine root litter.Of the soil compartments,one is for the soluble compounds of litter,one for holocellulose,one for lignin-like com-pounds and the other two for humus compounds.Each of the litter compartments has a speci fic fractionation rate (a i )and each of the soil compartments a speci fic decomposition rate (k i ).These rates determine frac-tions that are removed from the contents of the com-partments each year.Carbon removed from the litter compartments is divided into the soluble,holocellulose and lignin-like soil compartments according to the chemical composition of the litter (c i ).Compositionof litter from coniferous and deciduous trees is assumed to differ (Table 1).A part of carbon removed from the soil compartments (p i )is transferred to the subsequent compartment and the rest out of the sys-tem;from the second humus compartment,carbon is only transferred out of the system.Carbon input into the soil module is litter production calculated in the biomass and litter production module (Section 2.3).The fractionation rates (a i )and the decomposition rates (k i )depend on annual mean temperature (T )and the difference between precipitation and potential evaporation from May to September (P ÀE ):a i ðT ;P ÀE Þ¼1þð0:0937ðT À4ÞÞþ0:00229ððP ÀE ÞÀðÀ50ÞÞa 0(1)Fig.2.In EFISCEN,state of forest is depicted as an area distribution (hectares)over age and volume classes in volume –age matrixes (Nilsson et al.,1992).Growth is described as area changes to higher volume classes and ageing of forest is incorporated as a function of time up to the regeneration.Separate matrix is provided for each forest type provided in the inventory data used in the model.Regeneration after clearcut is through a bare-forest-land class to the first volume and age class (shown as disconnected line outside the matrix and then to the first volume and age class).90T.Karjalainen et al./Forest Ecology and Management 162(2002)87–103k i ðT ;P ÀE Þ¼1þs ð0:0937ðT À4ÞÞþ0:00229ððP ÀE ÞÀðÀ50ÞÞk 0:(2)These dependencies were established by reanalysing data on the decomposition of Scots pine needles across Europe (Berg et al.,1993).We assumed that the frac-tionation and decomposition rates of all kinds of litter were dependent on climate according to these equa-tions.The reference rates (a 0and k 0)were determined for conditions,where T ¼48C and P ÀE ¼À50mm by adjusting model-calculated mass loss rates to litter bag experiments (Berg et al.,1982,Berg et al.,1984)and model-calculated steady state amounts and accu-mulation rates of soil carbon to measured values (Liski and Westman,1995;Liski et al.,1998)(Table 1).Parameter s decreases the temperature dependence of humus decomposition (Liski et al.,1999;Giardina and Ryan,2000).It was set equal to 0.6for the first humus compartment and 0.36for the second one;it was equal to 1for the other compartments.The soil sub-model operates on a yearly time-step.It was initialised in this study by setting the compartmentsto steady state with the input of the first 5years (1990–1995).2.5.Forest management and wood products Forest management in EFISCEN model is described in terms of thinning and final felling regimes per forest type.The total volumes to be thinned and felled per tree species group as provided as input parameters.Final felling is expressed as a probability,which is depending on the stand age or on actual standing volume.These probabilities are converted into a proportion of the area in each cell that can be felled.The actual area felled in a cell depends on the requested volume to be harvested and on the volume available in the species group.A felled area is moved to a bare-forest-land class (Fig.2).Regeneration is represented as a transition of an area from the bare-forest-land class to the first volume and age class.The area that is regen-erated is regulated by a parameter that expresses the intensity and success of regeneration (young forest coef ficient).This parameter is a percentage of theareaFig.3.Flow chart of the soil carbon sub-model in EFISCEN.The boxes represent carbon compartments,the arrows carbon fluxes and the text by the arrows parameters controlling the fluxes.Parameter values at the reference conditions are given in Table 1.T.Karjalainen et al./Forest Ecology and Management 162(2002)87–10391in the bare-forest-land class that will move to the first volume and age class during the followingfive years.Part of the felled biomass is left in the forest (usually foliage,branches and roots)and part is removed from the forests to be used in forest industries and households.Harvested wood in EFISCEN model is processed into wood products in the wood product model that was adapted from Karjalainen et al.(1994).Coniferous and non-coniferous timber is transferred separately into several production lines like sawn timber,wood pulp (chemical and mechanical pulp,paper),wood-based panels(plywood,veneer and particle board)and fuel-wood.The model follows those production lines with country-or region-specific parameters for the wood processing industry and shares in consumption until the products are removed from use and the stored carbon is released back into the atmosphere.Manu-factured products are divided into seven usage cate-gories(short life paper products,long life paper products,packing materials,furnishing,structural support materials,building materials and other build-ing materials)with four different life span options to separate the different usage of wood products and their possible later re-use.At the end of its primary use, products can be either recycled or burned for energy production or disposed in landfills.In landfills,the disposed products decompose slowly,releasing car-bon into the atmosphere.In this study,landfills are excluded since there was not enough data available to initialise carbon stocks in landfills.The half-life period(life span)for the different product groups were50years for the long life span products,16years for medium-long life span products,4years for med-ium-short life span products and1year for short life span products.These life spans are similar or slightly shorter than in Row and Phelps(1990),Karjalainen et al.(1994)and Pingoud et al.(1996,2000). Running the model with harvesting data from1961 to1990has initialised the wood product stocks for products in use.Data from1961was also used for the years1931–1960.The data on historic removals (roundwood production)and commodities(fuelwood, sawn timber,wood-based panels and pulpwood)were taken from the FAOSTAT database on forestry (FAO,1998).The United Nation Statistical Division (UNSTAT)COMTRADE trade statistics(UN,1999) and one commodity producer supplied additional data.2.6.Impact of climate changeForest growth might change during20–50-year simulation periods,due to changes in the environment and in this case as a consequence of climate change. Therefore,the model has been modified to simulate the impact of such changes on growth rate.WhenTable1Parameters of the soil carbon sub-module at the referenceconditionsParameter ValueFractionation rate(per year)a nwl1a fwl0.5a cwl0.05Litter compositionc nwlsol for conifers0.27c nwlcel for conifers0.51c nwllig for conifers0.22c fwlsol for conifers0.03c fwlcel for conifers0.65c fwllig for conifers0.32c cwlsol for conifers0.03c cwlcel for conifers0.69c cwllig for conifers0.28c nwlsol for deciduous trees0.38c nwlcel for deciduous trees0.36c nwllig for deciduous trees0.26c fwlsol for deciduous trees0.03c fwlcel for deciduous trees0.65c fwllig for deciduous trees0.32c cwlsol for deciduous trees0.03c cwlcel for deciduous trees0.75c cwllig for deciduous trees0.22Decomposition rate(per year)k sol for conifers0.5k sol for deciduous trees0.8k cel0.3k lig0.15k hum10.013k hum20.0012Transfer proportionp sol0.15p cel0.15p lig0.18p hum10.18Annual mean temperature48C,the difference between precipitationand potential evaporation50mm.The fractionation and decom-position rates were dependent on climate according to Eqs.(1)and(2),the other parameters were similar for all conditions.92T.Karjalainen et al./Forest Ecology and Management162(2002)87–103changes in the growth occur,the transitions of area in the volume–age matrixes are adapted accordingly (Section2.2and Fig.2).Decomposition in the soil depends of the temperature,precipitation and evapo-ration conditions(Section2.4)and thus,changes in climate are included in the carbon dynamics in the soil. Climate change induced changes in the growth rates in the EFISCEN model are based currently on process model outputs.Process models simulate photosynth-esis and respiration of trees in hourly or daily time-steps.The performance of process models in relation to the short-and long-term dynamics of carbon exchange and forest growth rates have been evaluated in the project against the available forest ecosystem gas exchange data(short-term performance)and growth and yield data(long-term performance) (Kramer et al.,2001).Process models are run for selected representative sites and tree species.Growth of stemwood by stand age is compared under current and changing climate and the change in the growth is then used to modify growth in the EFISCEN model. Simulating forest growth with very detailed pro-cess-based models can only be executed at a limited number of sites because of the need for initialisation data and computing capacity.In order to upscale to regional,national and European levels,selected sites should represent the average growth conditions of different tree species in the pre-selected climate zones (northern boreal,southern boreal,maritime temperate, continental temperate,mediterranean)and should be related to the average values of the forest inventory data set which is based on countries and second-order administrative units.To select representative sites for each climate zone a GIS-based analysis was performed.A forest mask of the CORINE land cover map was extracted (CORINE,1997).For areas without CORINE land cover information the data set was completed with the ESA-ESTEC satellite-based forest–non-forest map (ESA,1992).This forest map was overlaid with a digital elevation data set,the FAO soil map(FAO,1994),the admin-istrative borders and the climate zones.Average climate(temperature,precipitation,growing season and moisture index)was derived from the Cramer–Leemans data set by using the climate module of the BIOME model(Prentice et al.,1992;Sykes et al.,1996)and interpolated on a10ftÂ10ft grid by using a thin plate interpolator(Hutchinson,1995). For each tree species simple rules were established which describe the geographic range of the species (Jalas and Suominen,1987a,b;Walter and Breckle, 1991).Then the area weighted mean of the climate parameters,the elevation and the latitude were calcu-lated per tree species and climate zone(Table2).A site was then selected where long-term Climatic Research Unit(CRU)data(University of East Anglia,Norwich) (Hulme et al.,1995;New et al.,2000)with compar-able average values was available(Fig.4).Because most of the models are very sensitive to global radia-tion the sites were also located close to stations where measured global radiation data was available(Global Radiation Atlas,Palz and Greif,1995).Another algo-rithm was performed to select the most common soil type for every tree species and climate zone.The simulation of forest growth,covering the whole rotation period,with different European forest types, requires long-term weather data sets with high tem-poral resolution.For the time period1901–1990,the monthly0:5 Â0:5 climate data set of CRU was available.To analyse the impact of climate change on forest growth the output of the Hadley Centre’s Climate model2(HadCM2)run based on emission scenario IS92a(Mitchell et al.,1995)was used. The global circulation model(GCM)results were downscaled to the sites by calculating the difference for each parameter between the time period1990–2100and the average values of the reference period 1931–1960using monthly time-steps.The time series of these anomalies were then added to the average values of the CRU data for the same time period.The historic period of climate data was extended with GCM data for the years1831–1900.Thus,forest growth could be simulated and results could be vali-dated over rotation periods of100years and more by taking into account the interrelationship between forest growth data and the historic climate conditions for which these data sets are valid.The monthly climate data were disaggregated with the C2W weather generator(Bu¨rger,1997),which had been fitted with climatological station data set to the con-ditions at the modelling sites.Daily relative humidity was then calculated from the minimum temperature, daily potential evapotranspiration and annual preci-pitation as described in Kimball et al.(1997).The global radiation was corrected with the data from theT.Karjalainen et al./Forest Ecology and Management162(2002)87–10393Table 2Tree species that are simulated at the different representative sites (see Fig.4)Climate zone Site number Country ElevationTree species11Sweden P .sylvestris ,P .abies ,Betula sp.22Sweden P .sylvestris ,P .abies ,Betula sp.33Denmark P .sylvestris 4Scotland Picea sitchensis5FranceP .sylvestris ,Q.robur 46Northern Poland <500m P .abies7Southwest Poland P .sylvestris ,Q.robur 8(Low)Austria <650m P .abies ,Abies alba 8(Medium)Austria 650–1150m P .abies ,A.alba 8(High)Switzerland 1150–1700m P .abies ,A.alba 9Slovakia 500–1000m P .abies ,F .sylvatica 10Romania P .sylvestris ,Q.robur511(Low)Northern Italy <1000m Q.pubescens11(High)Northern Italy 700–1600m P .sylvestris ,F .sylvatica 12(Low)Southern Italy <800mQ.ilex ,P .pinaster 12(High)Southern Italy 1000–1800m F .sylvatica13(Low)Northern Spain <1400m Q.ilex ,Q.pubescens 13(High)Northern Spain 500–2000m P .sylvestris14SouthernSpain<1250mm Q.ilex ,Pinus halepensis ,P .pinasterIn relation to the geographic distribution of the tree species and the forest inventory data the site conditions sometimes are not only linked to the forest covered areas but also to certain levels of elevation.Climate zones:(1)northern boreal;(2)southern boreal;(3)maritime temperate;(4)continental temperate;(5)mediterranean.Fig.4.Climatic zones and location of representative sites.Nineteen sites in five different climate zone were selected,each representing typical growth conditions for the most important tree species in European forests under northern and southern boreal,maritime temperate and continental temperate and mediterranean climate (see also Table 2).94T.Karjalainen et al./Forest Ecology and Management 162(2002)87–103European Radiation Atlas.Wind speed was obtained from measurements of climatological stations.The time series of wind speed data were then repeated as often as necessary to cover the whole time period. For the case study of Germany the output from the TREEDYN3forest simulation model(Bossel,1996; Sonntag,1998)was used to modify growth in the EFISCEN and to convert stem wood volumes to total tree biomass and for the calculation of litter input as explained earlier in Sections2.2and2.3.TREEDYN3 is a process-based model for tree growth,carbon and nitrogen dynamics of single species,even-aged stands. The model has been parameterised for Picea abies, Pinus sylvestris,Pinus pinaster,Quercus ilex and Fagus sylvatica.TREEDYN3has been applied to a number of sites throughout Europe in relation to long-term impacts of climate change on carbon dynamics and forest stand growth.Under changing climate,the net annual increment was higher than under current climate over the whole study period and by2050it was 13%higher.Under changing climate growing stock was11%higher by2050than under current climate.2.7.Calculation of the carbon budgetCarbon stocks and stock changes in tree biomass, soil and products are calculated per region but are usually presented by country.In order to allow com-parison with ecological studies,flux measurements and flux modelling,NPP(NPP¼gross annual increment plus biomass turnover in trees;also net tree biomass carbon balance plus litter production and timber har-vesting),net ecosystem exchange(NEE¼NPP minus heterotrophic respiration),NBP(NBP¼NEE minus biomass removed from forest),net product exchange (NPE¼biomass removed from forest minus carbon released from products;also net product carbon bal-ance)and net sector exchange(NSE¼NBP plus NPE; also NPP minus heterotrophic respiration minus carbon released from products)are calculated.Carbon budgets are presented as average values per hectare(average for the area)or for the whole area in consideration.3.Case study of GermanyThe forest inventory data used were based on the 1986–1990and the1993inventory cycle(EFISCEN’s European forest resource database,Schelhaas et al., 1999).On average,we assume1990to be the initial year.The input data distinguish13regions and nine species,covering9.9million ha of forest.According to the assessment of the forest resources of the temperate zone(FAO,1992),this is96%of the exploitable forest area in Germany.In relation to timber harvesting,we have continued the current harvesting levels as a‘‘business as usual’’TRADE felling data between1990and 1997gives an average of42.4million m3per year.We assumed41million m3per year as total fellings over bark throughout the simulation period.The proportion of coniferous species of the total felling was estimated to be33.1million m3per year and that of deciduous species9.6million m3per year(FAO,1992).We assumed that in coniferous stands45%of the total felling was thinning and in deciduous stands that it was52%.We also assumed that there will be no net forest area expansion within the simulation period. For the current climate,it was assumed that growth was similar to that measured in the late1980s and early1990s.Under changing climatic conditions the mean annual temperature increased by approximately 48C during the60-year simulation period,while precipitation increased only slightly(Fig.5),based on the output of the HadCM2run and emission scenario IS92a(Section2.6).At the beginning of the simulation net annual increment was9m3/ha per year,felling4m3/ha per year and growing stem wood stock266m3/ha as an average over the whole study area.The net annual increment declined slightly during thefirst20years, but more substantially after2010(Fig.6).This is due to the fact that the average age of the forests increased as a consequence of fellings being less than one-half of the net annual increment.The average age of the forests increased and thus,average growth declined. Nevertheless,the growing stock increased to over 500m3/ha by2050.The carbon stock at the beginning of the simulation, in1990,was860Tg C in tree biomass,623Tg C in soil and66Tg C in wood products.Hence,the total stock of German forests and wood products was 1549Tg C(Table3).Tree biomass contained55% of the total stock,soil40%and wood products5%.It should be noted that soil carbon stock includes only the carbon coming from tree biomass and therefore,T.Karjalainen et al./Forest Ecology and Management162(2002)87–10395。

775-784-4789.E-mail address:msg@(M.S.Gustin).1352-2310/02/$-see front matter r2002Elsevier Science Ltd.All rights reserved.PII:S1352-2310(02)00329-1from HgS is that the mineral is thermodynamically stable at high temperatures and reducing conditions and therefore,at low temperatures and oxidizing conditions it could degrade to Hg0(cf.Eh–pH diagram in Anderson,1979).HgS could also be degraded to Hg0 by microbially facilitated solubilization of Hg(II) simultaneously with oxidation of the sulfide to sulfate and subsequent reduction of Hg(II)to Hg0by an enzyme which is present in a number of bacteria(Wood, 1974).The photo-reactivity of HgS has long been noted in the literature and is readily observed in nature as red HgS turns to black with exposure to light(Kothny, 1971).Baily et al.(1959)suggested that the transforma-tion from red to black was associated with the formation of schuetteite(HgSO42HgO)when HgS and H2O reacted in the presence of sunlight.Davidson and Willsher(1981)and McCormack(2000)demonstrated that blackening of HgS occurred with the simultaneous interaction of light,water and halogens.The blackening of red HgS has also been observed for fresh pieces of HgS ore that have not been exposed to water.Dreyer (1939)suggested that the blackening was due to the development of colloidal Hg0produced by the degrada-tion of HgS in light.Other solid Hg phases known to be photo-reactive include:Corderoite—a Hg3S2Cl2, Radtkeite—Hg3S2ClI,and Kenhsuite—Hg3S2Cl2 (Foord and Berendsen,1974;McCormack et al.,1991; McCormack,1997).Sulfur and iron complexes have been demonstrated to participate in the photo-reduction of Hg(II)(cf.Stromberg et al.,1991;Lin and Pehkno-nen,1997).Light-enhanced emission of Hg from substrate has been observed in situ(cf.Gustin et al.,1998,1999;Carpi and Lindberg,1998;Zhang et al.,2001)and in the laboratory(Gustin et al.,1997,1998,1999).Gustin et al. (1997)noted that incident light increased Hg emissions from Hg contaminated mill tailings(Carson River Superfund Site)by1–2orders of magnitude above that measured in the dark at the same soil temperature.A significant enhancement in Hg emissions has been reported for a variety of naturally occurring Hg-enriched and background(o0.1m g Hg/g)substrates in the light relative to that occurring in the dark at the same substrate surface temperature(cf.Engle et al.,2001; Gustin et al.,1999;Zhang et al.,2001).Gustin et al. (1998,1999),using a controlled laboratory chamber, demonstrated that light-enhanced emissions occurred from substrate amended with pure HgS,from naturally Hg-enriched substrate,and very slightly from substrate amended with Hg0.They proposed two mechanisms for the light enhancement:photo-reduction of Hg(II)bound up as Fe-oxide or sulfur complexes and/or physical desorption of Hg0from substrate.They noted that some photoreactive gas species(i.e.Hg(SH)2(Stromberg et al., 1991))could be produced by weathering of HgS.Understanding the magnitude of emissions from natural substrates is critical for balancing the Hg global biogeochemical cycle,determining if controls on anthro-pogenic point sources will be effective,and assessing local,regional and global environmental impacts.In order to quantify emissions from naturally and anthro-pogenically enriched substrates,those factors most important in controlling emissions must be character-ized.This paper describes laboratory andfield studies designed to investigate the mechanism(s)of light-enhanced Hg emissions from substrate.This paper presents investigations of light-enhanced Hg emission from substrates amended with synthetic Hg species,and naturally and anthropogenically enriched in Hg.For those substrates naturally enriched in Hg,the phases present were identified in order to see if a link between substrate Hg speciation and light-enhanced emissions could be established.The working hypotheses were that photo-reduction of solid or gaseous Hg phases,and desorption of Hg0are mechanisms respon-sible for the light-enhanced emissions.2.MaterialsMercury emissions were measured in the laboratory from synthetic Hg chemicals that were amended to ground glass,autoclaved Pyramid Lake sand(3%silt and clay(o0.064mm grain size),97%sand,and0.13% organic carbon),ground glass coated with Fe oxide,anda river bank sediment(88%sand,22%silt and clay,and3.03%organic carbon)(cf.Sladek and Gustin,2002) (Table1).Synthetic Hg species consisted of Red Hg(II)S (Aldrich Chemical99%),electronic grade Hg0(Aldrich Chemical99.999%),Hg2Cl2(ACS reagent grade99.6% Sigma)and HgCl2(Sigma95%).Soluble species(Hg-chlorides)were added in solution to substrate,which was subsequently dried using a N2gas head space.Hg0 and HgS were added dry to substrates and then ball rolled or shaken to homogenize.A Hg permeation tube (VICI Metronics)was used to generate Hg0gas. Natural and anthropogenic Hg-enriched substrates for which light-enhanced emissions were investigated in the laboratory included:mill tailings from the Carson River Superfund Site(located east of Reno,Nevada (NV),USA)to which Hg0liquid was added to extract gold and silver from ore;naturally Hg-enriched sub-strate and processed mine waste from the Knoxville Mining District(located in central California(CA), USA)),the New Idria Mining District(located in south-central CA),and the Sulphur Bank Superfund Site (located in central CA);and cinnabar(HgS)ore from the Ivanhoe Mining District(located in north-central NV)(Table2).In situ Hg emissions were measured at the Carson River Superfund Site,the New Idria mining district,the Sulphur Bank Superfund Site,the IvanhoeM.S.Gustin et al./Atmospheric Environment36(2002)3241–3254 3242Mining District,in the Long Valley Caldera(near Mammoth,CA)and from the Steamboat Springs Geothermal Area(located just south of Reno,NV). One set of in situfield chamber measurements were made on Hg-amended soils at the Great Basin Environ-mental Research Laboratory at Desert Research In-stitute,Reno,NV.The soil was housed in7.3Â5.5Â4.5m3(lÂwÂd)enclosed chambers or mesocosms (EcoCELLS)designed as openflow mass balance systems(cf.Griffin et al.,1996).Each EcoCELL had three soil containers with B5tonnes of gravel overlain by B4.5tonnes soil with a total CELL soil surface area of11.2m2.The soil consisted of a1:1ratio of sand and loam amended with mill tailings(500m g Hg/g)from the Carson River Superfund Site to achieve a Hg concen-tration of1271m g/g.The experimental design of the EcoCELLs allowed for precise manipulation of envir-onmental conditions and measurement of system level response with high resolution.Air temperature within the cells was maintained at constant261and181C during the day and night,respectively.Incident light and soil surface temperatures were uncontrolled parameters during the daytime for the CELLs were naturally lit.All natural wavelengths of light(measured with an Ocean Optics s Spectrometer)passed through thefield chamber in the EcoCELLs.The light intensity in the EcoCELLS was such that visible light was reduced by B37%and ultraviolet light by50%relative to outside.The intensity of ultraviolet light passing through thefield chamber, used to directly measure Hgflux from soil,was approximately5%less than that entering the Eco-CELLs,while the intensity of visible light in thefield chamber was B15%less than that in the EcoCELLs.2.1.Determination of Hg speciation in substrate Mercury speciation for some substrates used in the laboratory experiments was determined using a thermal desorption–decomposition method(cf.Biester and Scholz,1997;Biester et al.,1999),and extended X-ray absorptionfine structure spectroscopy(EXAFS)(cf. Kim et al.,2000).The solid phase desorption technique identified Hg minerals and phases in substrates based on comparison of desorption temperatures with those determined for pure Hg minerals or phases.EXAFS entailed the use of high energy X-rays to excite or eject electrons,inducing electronic scattering interactions between the central absorbing atoms and those sur-rounding(Kim et al.,2000).The scattering patterns are then used in a linear least-square combination analysis to identify the mercury species in substrate based on patterns for known pure compounds.Application of both methods is limited by the high detection limit needed for species identification(B100m g Hg/g),and byTable1Ratio of mercury emissions measured from substrate in the light to that in the dark using the gas exchange chamber and associated activation energiesSubstrate E a Conditions Statistics Light:Dark Red Hg(II)S amended to Pyramid Lake sand10.5Dark R2¼0:98;p o0:059.5100Light R2¼0:99;p o0:069.1Dark R2¼0:87;p o0:22 6.382Light R2¼0:98;p o0:07Crushed HgS ore amended to ground glass22.6Dark R2¼0:78;p o0:12 5.6149Light R2¼0:88;p o0:2Hg0amended to Pyramid Lake sand10.8Dark R2¼0:90;p o0:05N/AHg0amended to Fe-oxide coated glass18.8Dark R2¼0:95;p o0:05 1.3555.4Light R2¼0:88;p o0:05Hg0amended to sediments with3%organic material 6.7Dark R2¼0:97;p o0:07 1.240.7Light R2¼0:98;p o0:098.6Dark R2¼0:99;p o0:0542.7Light R2¼0:90;p o0:07HgCl2amended to ground glass17.3Dark R2¼0:98;p o0:05N/AHgCl2amended to Fe-oxide coated glass15.7Dark R2¼0:95;p o0:11916.9Dark R2¼0:99;p o0:0551.3Light R2¼0:99;p o0:05HgCl2amended to sediments with3%organic material7.0Dark R2¼0:89;p o0:20 1.328.7Light R2¼0:95;p o0:145.2Dark R2¼0:75;p o0:1238.7Light R2¼0:99;p o0:05Mill tailings from the Parke and Bowie Mill at Carson River Superfund Site18.9Dark R2¼0:99;p o0:0518152Light R2¼0:97;p o0:06M.S.Gustin et al./Atmospheric Environment36(2002)3241–32543243the availability and overlap of desorption curves and EXAFS spectra for Hg species and phases(Sladek et al., 2002).boratory measurement of emissionsMercury emissions were measured under controlled environmental conditions using a laboratory gas ex-change chamber(cf.Gustin et al.,1997,1998,1999). Experiments were done with pure air generated using an Aadco s pure air generator(0ng/m3)for pure Hg phases,and with laboratory air(2–6ng Hg/m3)for natural substrates.Temperature of the air and substrate within the chamber,monitored using thermocouples (OMEGA s)and an infrared sensor(Everest Inter-science s)were averaged and recorded using a data logger(Campbell Scientific s).Substrate were intro-duced to the chamber and allowed to equilibrate for24h before experimental manipulations commenced(cf. Gustin et al.,1997).Mercury concentrations at the inlet and outlet of the chamber were measured in5-min intervals using a Tekran s2537A Cold Vapor Atomic Fluorescence Spectrometer and a Tekran Automated Dual Sampling unit.Measurement of Hg air concentra-tions in5-min intervals by this system allowed for assessment of almost real timeflux and of the influence of environmental parameters on Hgflux(Gustin et al., 1999a)Mercuryflux from substrate was determined using the following equation:F¼Q nðC oÀC iÞ=A;where F is the totalflux in ng Hg/m2h;C o and C i are the Hg concentration of outlet and inlet air in ng Hg/m3, respectively;A is the surface area of substrate in m2;and Q is theflow of air through chamber in m3/h.Flow of air into the chamber was controlled between5and10l/min. Chamber blanks,represented by the difference in the Hg concentration of outlet air and inlet air,were measured routinely between experiments and ranged from0.1to 0.2ng/m3.Reportedfluxes represent at least threeflux measurements with a coefficient of variation of o5%. For most of the gas exchange experiments a1–2mm thick layer of substrate was placed in a petri dish in the chamber.One set of experiments entailed burial of Hg emitting material beneath a0.5–1cm layer of quartz sand.Light wavelengths,generated using a Xenon arc lamp,transmitted through the Pyrex chamber were >500nm determined using an Ocean Optics s Spectro-meter.Light intensity was adjusting using the voltage to the lamp and the light-driven emissions were compared to those in the dark at the same surface temperature at the highest light intensity(600m mol/m2s).Light inten-sities were varied to investigate the influence of light onflux at40,200and600m mol/m2s measured with a Li-Cor250quantum sensor.2.3.In situ measurement of mercury emissionsIn situ Hg emissions reported in this study were measured using a cylindrical polycarbonatefieldflux chamber with a radius of10cm,a height of3.5cm,and a 1l volume(cf.Engle et al.,2001;Gustin et al.,2002)or with a Modified Bowen Ratio micrometeorological method(cf.Lindberg et al.,1995;Meyers et al.,1996; Gustin et al.,1999a),and a Tekran(Model2537A) CVAFS–TADS system.Mercuryflux for thefield chamber measurements was calculated using the same equation described above for the laboratory chamber. The chamberflow was controlled between5and10l/ min.Coincident with the measurement of Hgflux,air and substrate temperature(OMEGA s thermocouples), and incident light(Li-COR s LI200x)were averaged and recorded for5-min intervals using a data logger (Campbell Scientific s CR21X).As mentioned,both visible and ultraviolet wavelengths of light passed through thefield chamber.Total Hg concentration of substrates was determined using cold vapor atomic absorption spectroscopy after aqua regia digestion(Lechler,1999).Statistical analyses of data were done using STATVIEW(SAS Institute, Inc.).3.Results and discussion3.1.Amended substratesDetectable amounts of mercury were constantly emitted from all synthetic Hg species(HgS,HgCl2, Hg2Cl2and Hg0)in the dark and light.Of the pure synthetic Hg species amended to quartz sand,HgS was the only species that exhibited light-enhanced emissions above that occurring in the dark at the same substrate temperature(Table1).Gustin et al.(1998)reported similar results.Emissions from natural(Ivanhoe cinna-bar ore)HgS at401C in the light(170.5ng/cm2h)and dark(0.170.02ng/cm2h)occurred continuously(mea-sured over48h)within the gas exchange chamber. Emissions from HgS were enhanced by6–10times immediately with incident light and returned to dark emission rates as soon as light exposure ceased.In order to determine if Hg bound to iron oxides and organic matter in substrate would be released through photo-induced desorption of Hg0or photo-reduction, experiments were done using HgCl2,Hg0and Hg2Cl2 amended to iron oxide and organic containing sub-strates.Light-enhanced emissions above that occurring in the dark at the same surface temperatures were observed for all substrates except those containing Hg2Cl2(Table1).For those substrates exhibiting light-enhanced emis-sions,Hgflux increased as a function of increasing lightM.S.Gustin et al./Atmospheric Environment36(2002)3241–32543245intensity (Table 1;Fig.1).The slope of the curve describing the logarithm (log)of Hg flux as a function of temperature in the dark for the synthetic HgS amended substrate (m ¼0:021;p o 0:05;r 2¼0:98)was significantly less than that describing the log of Hg flux and soil temperature at different light intensities (m ¼0:188;p o 0:05;r 2¼0:97)and slightly less than that describing the slope of the vapor pressure curve for Hg of 0.035(cf.Gustin et al.,1997).The slope of curves describing the log of emissions from Hg 0amended organic containing sand and HgCl 2amended Fe oxide and crushed HgS ore in the dark roughly paralleled the slope of the curve describing the vapor pressure for Hg 0(Fig.1).This was also observed for emissions from Hgcontaminated mill tailings in the dark (Gustin et al.,1997).This suggests that in the dark solid Hg phases constantly release Hg 0through chemical deterioration.A useful parameter for understanding the processes involved in volatilization or the release of Hg from substrate is the activation energy.The activation energy (E a )is calculated using the Arrhenius equation:ln K ¼ln A ÀðD H =RT Þ;where A is a frequency factor or the number of times the atoms are close enough to react,D H is the E a or molar heat of vaporization (kcal/mol),T is the absolute temperature (1K)and K is a rate constant which may be equated with Hg flux measured at specific tempera-tures (cf.Lindberg et al.,1979,1995;Gustin et al.,1997;Carpi and Lindberg,1998;Zhang et al.,2001).The E a for the volatilization of Hg 0liquid is 14kcal/mol at 251C (Lide,1993).The E a calculated for synthetic HgS and Hg 0amended Pyramid Lake Sand in the dark was slightly less than the E a for the vaporization of Hg 0liquid.This may be due to a higher temperature range used to generate the data for the E a calculated in Table 1(27–421C).Natural HgS ore had a higher E a calculated for emissions in the dark than the pure HgS.This is most likely due to the fact that the HgS ore was made up of dense silica and cinnabar,whereas the synthetic HgS was a pure fine powder.For HgCl 2and Hg 2Cl 2amended sand the calculated E a s were higher (20–25)than that for volatilization of Hg 0in the dark indicating that the more oxidized chloride species are not as readily degrading to Hg 0as the more reduced forms.The E a calculated using substrate temperature,adjusted by varying light inten-sity,and Hg flux for the pure and natural HgS containing substrates were significantly higher than E a for Hg 0volatilization indicating that additional energy was being consumed in the process of releasing Hg 0,and that photo-reduction was occurring (Table 1).To investigate whether gaseous Hg species or Hg 0,derived from solid Hg phases and moving upthrough substrate,were being photo-reduced or desorbed,respectively,upon interaction with light at the air:soil interface,emissions were measured from Carson River mill tailings,crushed HgS ore and a Hg 0permeation tube buried beneath clean quartz sand.Emissions of Hg constantly occurred from the buried material indicating that Hg vapor was constantly being produced and migrating towards the air–substrate interface.No enhanced emissions were observed with incident light indicating that photo-reduction of gaseous phases,such as Hg(SH)2,being emitted from the buried materials was not occurring (Fig.1).To address the hypothesis of Gustin et al.(1998),that Hg 0migrating from depth and oxidized and bound to iron oxides at the air:surface interface is subsequently released by photo-reduction,3experiments were done using the same buried materials above.For each,alayerHg o amended organic containing sediment2530354045Temperature,oCl o g n g H g /m 2hHgCl 2amended iron oxide coated sand2530354045Temperature,oCl o g n g H g /m 2hHgS2530354045Temperature,oCl o g n g H g /m 2hFig.1.Logarithm of mercury flux from amended substrates as a function of temperature in the light (lt)and dark (dk).Light data was obtained by adjusting light intensity and dark data by manipulating temperature.Flux was also measured from natural HgS covered (c)with a layer of sand in the dark (c-dk)and in the light (c-lt).Also shown is the line for the vapor pressure curve for elemental mercury (vp).M.S.Gustin et al./Atmospheric Environment 36(2002)3241–32543246of iron oxide coated quartz was placed on top of the quartz sand beneath which was the gaseous Hg emitting material.No light-enhanced emissions were observed.In one experiment the layered substrate(Hg permeation tube,quartz sand,iron oxide coated quartz)was placed in a fume hood for a week providing for interaction of the Hg0,Fe oxide and ambient lab air.No light enhancement of emissions was observed for subsequent exposures in the gas exchange chamber.These experiments indicated that HgS,as well as HgCl2and Hg0liquid amended to iron oxides and organic containing substrates participate in photo-induced emissions of Hg from substrate.Interaction of Hg0gas with iron oxides does not elicit the same response as Hg0liquid.3.2.Natural substratesAll natural samples used in the gas exchange chamber exhibited light-enhanced emissions of Hg with incident radiation relative to that occurring in the dark at constant substrate temperature(Fig.2a)Note that emissions have been normalized based on the Hg concentration in the substrate).The ratio of Hgflux in the light to that in the dark at350ranged from1.4to116 with the highest ratios associated with the Park and Bowie tailings sample and altered andesite from Sulphur Bank Superfund Site(Table2).Light-enhanced emis-sions were measured from duplicate samples from the Knoxville District(KMD-M),New Idria District(IMD-CC)and Sulphur Bank(SBSS-AA2)and the same degree of light enhancement was measured(Fig.2b, Table2).Light-enhanced emissions were measured from samples taken from two different locations at the Bessel Mill tailings and the same degree of light enhancement was observed(Table2).Gustin et al.(1999)reported a similar range in the light-to-dark ratio of Hg emissions at constant temperature for substrate collected from the Steamboat Springs Geothermal area,south of Reno, NV,the Clyde Forks Mineralized Fault Zone,Ont., Canada,Proterozoic Black Shales from Canada,and the Carson River Superfund Site,NV.They found that light-enhanced emissions from tailings from the Carson River Superfund site were highest,being14.5times greater than those in the dark at the same temperature. For the other substrates light emissions were1.1–4times greater than those measured in the dark at the same surface temperature.The Hg speciation in substrate used was investigated to see if this would explain the variability in the amount of light enhancement.No Hg0was identified by thermodesorption in any samples and EXAFS cannot identify Hg0.Sladek et al.(2002)through selective extractions found o0.7%volatile Hg in some of the samples used in this study.Considering the high concentration of Hg in the natural samples used in this study,samples could contain100–10s of thousands of ng of Hg0,so its presence and release cannot be ruled out.In general,natural substrates identified by EXAFS as having>65%combined HgS and metacin-nabar(mHgS)exhibited a higher degree of light enhancement(light:darkflux ratio>3)than samples having primarily cinnabar or a lesser amount of cinnabar and mHgS combined(1.4–3times greater emission in light).Samples for which thermodesorption analysis identified matrix bound Hg,which includes Hg bound to iron,sulfur and organic phases,and mHgS,exhibited a higher degree of light-enhanced emissions than those identified as having predominantly cinnabar.Samples of rock material and soil from the New Idria mining district(IMD),for which cinnabar was identified by EXAFS as the predominant mineral,had the lowest light-enhanced emissions of all the samples.A calcine sample(processed Hg ore)from Aurora Mine(IMD-A), identified by EXAFS as having HgO and mHgS, exhibited a higher degree of light-enhanced emissions relative to other samples from the district.The ratio for light:dark emissions for substrate from New Idria district were less than that found for pure HgS amended sand(6–10)(Table1).Both EXAFS and thermodesorp-tion identified cinnabar as the predominant Hg phase in0.0010.010.1110100KMD-KMD-KMD-KMD-CRSS-BMCRSS-BMCRSS-PIMD-SIMD-IMD-CIMD-CIMD-SBSS-WSBSS-AASBSS-SBSS-AASBSS-AA IngHg/m2hpergmsHginsubstrate1101001000KMD-KMD-KMD-KMD-CRSS-BMCRSS-BMCRSS-PIMD-SIMD-IMD-CIMD-CIMD-SBSS-WSBSS-AASBSS-SBSS-AASBSS-AA Ilight:darkFig.2.(a)Histogram showing Hgflux measured in the light and dark from natural samples at351C normalized to the total mercury concentration in substrate using the gas exchange chamber.(b)Histogram showing light:dark ratio at351C of mercury emissions for natural samples measured using the gas exchange chamber.M.S.Gustin et al./Atmospheric Environment36(2002)3241–32543247the Clear Creek soil(IMD-CC)for which light-enhanced emissions were about1.6times that measured in the dark,significantly less than that obtained for pure synthetic HgS and forfinely crushed cinnabar ore (Table2).This difference is most likely due to the fact that the pure HgS consisted of afine powder and the HgS ore was crushed,while the natural samples consisted of aggregates of minerals with Hg species not as available for interaction with light.Those samples containing mHgS and cinnabar as identified by EXAFS exhibited a significantly greater degree of light enhancement than those samples with only HgS identified.Thermodesorption analysis identi-fied matrix bound Hg in all samples that EXAFS analysis identified mHgS.It is possible that the matrix bound Hg is mHgS because Biester et al.(2000) presented a Hg release curve for mHgS that overlapped the temperature range where matrix bound Hg is released.Although mHgS is considered the high temperature form of HgS that will transform to cinnabar at1bar3441C(Dickson and Tunnell,1959), it is produced in the laboratory and in natural environments at low temperatures(Pacquette and Helz, 1997;Barnett et al.,1997;Ravichandran et al.,1999). Metacinnabar,whether a high or low temperature form is the less stable form of HgS,and this perhaps would facilitate the photo-induced production and release of Hg0from this phase.Mill tailings samples from the Carson River Super-fund site,where Hg0liquid was anthropogenically amended to substrate,exhibited a significantly higher Hgflux response to incident light than most other natural l tailings from the Carson River Superfund site were identified as having primarily matrix bound Hg by thermodesorption analysis,and cinnabar and mHgS by EXAFS(Table2).Sladek and Gustin (2002)found,using back-scatter and energy dispersive X-ray analysis,that Hg was associated with silver–sulfur,iron–sulfur,gold–silver and sulfur containing phases.The high light-enhanced response seen with tailings samples may be due to the photo-reduction of Hg in these phases.In addition,the high surface area of the tailings,which consisted of predominantly silt and clay-sized grains,could have further exacerbated the l tailings from the Parke and Bowie Mill consistently exhibited a higher degree of light-enhanced emissions than those from Bessel Mill.The difference in the degree of light-enhanced emissions between sub-strate from the two mill tailings sites is perhaps an artifact of differences in ore processing.Bessel Mill was a site of primary ore processing while the Park and Bowie Mill was a site of tailings reprocessing(Anasari, 1989).Reprocessing could have further depleted the primary ore mineral,argentite(AgS),in Ag and resulted in increasing S sorbtion sites for Hg,perhaps forming mHgS.The highest light-enhanced Hg emissions occurred from altered andesite taken from the Sulphur Bank mine open pit.Although EXAFS and thermodesorption analysis were not performed for the exact samples used in the gas exchange chamber,EXAFS analysis has identified the mineral Hg3S2Cl2in samples from Sulphur Bank(Kim et al.,2000).Corderoite is a photo-reactive Hg species(McCormack,2000).Fig.3illustrates the light-enhanced emissions of Hg measured in the gas exchange chamber as a function of time at constant temperature for several natural samples.For each there was an initial pulse of Hg released with thefirst light and then the emissions remained higher than they were in the dark.As seen with Carson River Superfund Site-Parke and Bowie Mill20000400006000080000100000120000140000160000180000200000110011251150121512401305timengHg/m2hNew Idria District-Clear Creek Site2000400060008000100001200010101035110011251150timengHg/m2hKnoxville District-McLaughlin Mine12251250131513401405timengHg/m2hFig.3.Graphs illustrating the effect of light on emissions from three natural samples measured in the gas exchange chamber with soil temperature maintained at35711C.Vertical line indicates when the light was turned on.M.S.Gustin et al./Atmospheric Environment36(2002)3241–3254 3248。

由于特殊的物理化学性质，汞是通过大气进行长距离跨国界传输的全球性污染物；同时汞，尤其是甲基汞是对人体健康危害极大的有害物质。

随着近年来经济的快速发展，我国已成为全球人为活动向大气排汞最多的国家之一，这已引起了国际社会的广泛关注。

但是目前关于我国人为活动向大气的排汞量的估算误差很大，同时对我国自然过程向大气的排汞量还认识不清。

这对我国将来开展汞的环境外交谈判极其不利。

另一方面，目前在北美和北欧普遍出现偏远地区陆地水生生态系统鱼体汞含量升高的现象，我国如此大量向环境排汞，是否也会出现类似的水生生态系统汞污染的问题还不清楚。

西方一些政客开始指责中国的环境汞污染问题，一方面他们指责我国排放的汞对北美和北欧的环境产生影响，另一方面，他们认为我国排放的汞造成我国水产品的严重汞污染。

但近年来，我国对环境汞污染的研究严重滞后，无法对上述质疑进行准确回应。

针对以上情况，我实验室科研人员在汞的自然过程和人为活动向大气汞的排放及对我国大气环境影响和汞在环境中甲基化特征及对人体健康影响方面开展了系统工作，取得重要进展，为科学认识我国人为活动向大气的排汞量、自然过程排汞对大气汞污染的影响及我国汞排放对居民健康影响提供重要的基础数据。

研究表明，我国环境汞污染问题与北美和北欧情况完全不同。

研究成果的主要进展表现在以下几方面。

1、不同汞排放源的排汞量和我国典型区域大气汞的分布及沉降通量研究（1）我国人为活动的向大气的年排汞量比西方学者估算的要低对燃煤、锌矿冶炼、汞矿冶炼和垃圾填埋等人为活动向大气的排汞过程进行了详细研究。

测定了不同燃煤锅炉排放烟气中不同形态汞的含量及燃煤过程向大气排放不同形态汞的释放因子；估算了贵州省燃煤向大气的排汞通量。

利用质量平衡原理，计算了土法炼锌、工业炼锌和土法炼汞过程向大气的排汞因子，通过对排放烟气中不同形态汞含量的测定，确定了炼锌和炼汞过程向大气排汞的形态分布特征，揭示了贵州锌矿冶炼和土法炼汞是区域大气汞的重要排放源。