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尹晓梅, 石广玉. SLCPs及其气候效应研究进展. 地球科学进展, 29(10): 1110-1119
Yin Xiaomei, Shi Guangyu. Advances in Studies of Short-lived Climate Pollutants. Advances in Earth Science, 29(10): 1110-1119  
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SLCPs及其气候效应研究进展
尹晓梅1,2, 石广玉1
1. 中国科学院大气物理研究所大气科学和地球流体力学数值模拟国家重点实验室(LASG),北京 100029
2. 中国科学院大学, 北京 100049

作者简介：尹晓梅(1988-),女,山东烟台人,博士研究生,主要从事气溶胶同化系统的模拟验证研究. E-mail: yinxiaomei@lasg.iap.ac.cn

基金:国家自然科学基金重点项目“大气棕色云的辐射增温效应”(编号：41130104); 国家自然科学基金项目“大气气溶胶携带的微生物在输送过程中的变性研究”(编号：41475136)资助
摘要

CO2造成全球55%~60%的辐射强迫,迅速有效的减排是对抗气候变化的必要措施,但必须与造成另外40%~45%气候效应的短期气候污染物(SLCPs)减排并行。SLCPs直接或间接地影响地球气候系统的辐射平衡及温度变化,危害生态系统和人类社会安全。控制SLCPs的排放能在短时间内缓解近期全球变暖和海平面上升,弥补CO2减排效应的滞后。在调研大量文献的基础上,首先论述了SLCPs研究的意义所在,归纳了SLCPs减排对全球气候变化的缓解效应。然后对SLCPs 4种代表物质——黑碳、甲烷、对流层臭氧和氢氟碳化物的物理及光学特性、排放变化和时空分布及未来发展可能的趋势进行了分析,在此基础上总结了分别针对4种物质的减排方案。阐述了4种SLCPs物质在不同机制下产生的直接和间接气候效应,以及对应的气候效应发生的机理和相关的大气化学过程,最后总结了国内外在研究SLCPs的大气浓度、区域排放、气候效应、辐射强迫及减排措施的研究方法,指出了研究中存在的不确定性因素及解决方案。

关键词: SLCPs; 气候因子; 气候变化; 减排
中图分类号:P467 文献标志码:A 文章编号:1001-8166(2014)10-1110-10
Advances in Studies of Short-lived Climate Pollutants
Yin Xiaomei1,2, Shi Guangyu1
1. Institute of Atmospheric Physics, Chinese Academy of Sciences. Beijing 100029, China
2. University of the Chinese Academy of Sciences. Beijing 100049, China
Abstract

Pollutants that contribute significantly to climate change over days to decades timescales have been defined as Short-Lived Climate Pollutants (SLCPs). SLCPs are climate forcers and environment pollutants, which have an effect on earth’s radiative balance, influence the global temperature and climate system through different ways. They also have adverse effects on the ecosystem and human society directly and indirectly. Mitigation emissions of the four SLCPs, black carbon, methane, troposphetic ozone and hydrofluorocarbons are the most effective strategy for constraining global warming and the rising of sea level as an important complement to reducing long-lived warming gases in the near term. In this paper, we summarized the significance of SLCPs research, pointed out the potential benefits of SLCPs emission reductions. They offered important policy opportunities to reduce radiative forcing and air pollution effects in short term. Then, we explained the physical and optical characteristics of SLCPs, illustrated how they contributed to the regional and global climate by interactions with clouds, ice, snow or other aerosols, discussed the present and future trends of their distribution and radiative forcing, summed up their direct and indirect climate effects and mechanism that are comprehensive in inclusion of all known and relevant processes and proved estimates of main forcing terms. At the same time, the advances in research methods and SLCPs climate effects as well as changes in climate forcing were also introduced in this article. We concluded the potential trends of SLCPs concentration in the atmosphere, pointed out the uncertainties factors in researches and relevant potential measures to reduce harmful emissions, which can slow the rate of climate change and protect the people and regions most vulnerable over the next several decades.

Keyword: Short-lived climate pollutants; Climate factors; Climate change; Emission reduction.

IPCC第五次评估报告(AR5)指出, 短期气候强迫因子(Near-term climate forcers, NTCF)对气候的影响主要发生在排放到大气中的前十年, SLCPs(Short-lived climate pollutants)是NTCF的首要成分, 主要包括黑碳气溶胶(Black Carbon, BC)、甲烷(Methane, CH4)、对流层臭氧(Tropospheric O3)和部分氢氟碳化物(Hydrofluorocarbons, HFCs)等[1], 其气候效应随排放的停止而快速减弱, 大气寿命是研究的关键。排放源的位置及气体在大气中的系列反应影响其在大气中的存留时间即周转期; 评估气候效应及反馈时, 扰动寿命更精确, 它表征脉冲排放到大气中气体的衰减, 描述气体在源强度进一步变化后所做的调整[1~3]; 联合国环境规划署(UNEP)报告对大气寿命的定义如下：停止排放后67%的气体分子从大气中移除所需的时间[4]。作为气候强迫因子, SLCPs对全球变暖的贡献率占40%~45%, 增温效应仅次于CO2[5]; 同时SLCPs也影响海陆生物圈N、S等的沉积。有针对性的SLCPs减排, 对稳定气候系统和缓解全球气候变化, 减少中纬度热浪、洪涝干旱和飓风等极端天气, 减缓格陵兰和北极冰雪融化及海平面上升, 维护自然和人类社会安全、保护气候脆弱区等的作用不容忽视。作为污染物, SLCPs减排能阻止每年几百万的过早死亡率和几百万吨的粮食产量损失, 促进可持续发展; 同时又能间接促进新能源的开发利用。SLCPs减排以较低成本快速弥补CO2减排效应的滞后, 为不可避免的气候变化争取应对时间, 但不能逆转全球变暖长期趋势, 必须继续推动长寿命温室气体(Long-lived Greenhouse-gas, LLGHG)的减排、管理和研究, 争取将全球增温幅度控制在合理范围内。

1 研究意义
1.1 SLCPs减排的重要性

持续的全球变暖和反常气候导致的灾难增多已成为各大洲难以幸免的客观事实[6]。北极和高纬地区增温迅速, 短期可能因高寒冻土融化和生物多样性减少而引发CO2大量排放。目前全球气温比工业革命之前升高了0.8 ° C, 2010年12月联合国气候变化框架公约(United Nations Framework Convention on Climate Change, UNFCCC)评估增温应控制在2 ° C以内。SLCPs排放区域差异大, 北半球中纬度、人口聚集区及工农业发达地区是高值区(图1)。

Fig. 1 SLCPs的全球分布图(a)2000年BC全球排放分布图(Gg)[7]; (b)2000年对流层O3的柱含量分布图(多布森)[8]; (c)2003— 2005年CH4柱平均摩尔分子分布图(× 10-9)[9]Fig. 1 Global distribution of SLCPs(a)BC emissions (Gg) of 2000[7]; (b)Tropospheric column ozone (Dobson) of 2000[8]; (c)CH4column averaged mole fraction(× 10-9) of 2003-2005[9]

表1 本世纪全球平均温度和海平面变化[10] Table1 Projected temperature change (Δ T) and SLR (Δ SLR) [10]

SLCPs减排可在10年内防止90%预测增温的发生, 余下的10%因海洋热力惯性延迟数百年。截至2050年：单独控制HFCs排放可避免大概20%(0.1 ° C)的增温, CH4减排措施会缓解全球升温0.3 ° C, 改善环境质量, 提高粮食安全, 增加清洁能源的使用[11]。BC+CH4减排避免全球增温0.5 ° C, 全球增温幅度减小1/2, 北极减少2/3, 青藏高原和西藏地区至少减小1/2。BC+O3+CH4减排, 分别使2040年和2070年北极避免0.7 ° C和0.84 ° C的增温。SLCPs同时减排, 2030年全球平均增温速率减缓50%~60%, 2050年避免升温0.3 ° C~0.8 ° C, 21世纪末海平面上升缓解22%~42%。若推迟SLCPs减排, 2050s的增温幅度将突破1.5~2 ° C, 海平面上升的缓解效应减弱1/3。从长远考虑, SLCPs应与CO2减排同时进行, 使未来30全球平均升温控制在1.5 ° C, 60~90年控制在2 ° C, 海平面上升缓解31%~50%(最高缓解35 cm(表1) [5, 10, 12, 13]。

1.2 SLCPs性质及气候效应

1.2.1 黑碳气溶胶(BC)

BC是强吸光不定型碳质气溶胶, 大气寿命几天到几周[2]。人为源主要是固体燃料的不完全燃烧, 自然源包括火山爆发和林火等。目前全球主要BC源来自亚洲、拉美和非洲, 尤其是生物质燃烧区。BC时空分布不均且大气浓度低(不到气溶胶的10%), 偏远和人口密集区的浓度差可达3个量级[14], BC广泛分布于土壤、雪冰、海洋湖泊沉积物和大气中[15]。BC百年增温潜能GWP100=900(120~1800)。1950— 1990年化石燃料燃烧的BC排放量增加了近3倍(2.2~6.7 Tg/a); 2000年全球总排放量7 500 Gg/a (2000~29000 Gg/a)[16, 17]。单位生物燃料燃烧持续排放的BC在20年和100年的地表温度响应指数(Surface temperature response per unit continuous emissions, STRE)分别为4 500~7 200, 2 900~4 600和2 100~4 000, 1 060~2 020[18]。

BC吸收所有波长的入射和出射辐射, 影响地表温度垂直分布, 喜马拉雅高原区50%的升温由BC的直接加热引起[19, 20]。对大气不均匀加热能改变大气环流及对流、大气稳定度和相对湿度, 影响全球水循环; 冰雪等高反射表面的BC减小地表反照率, 使区域升温, 加速冰雪融化, 极区对BC增温极其敏感(1890— 2007年北极增温1.9 ° C, BC引起1 ° C)[21, 22]。BC与不同相态的云相互作用, 改变云寿命、光学和微物理特性, 扰乱降水。参与污染物的气— 粒转化, 改变云滴数目、尺寸和云的反照率(第一类间接作用); 改变云生命期、液水含量(Liquid Water Content, LWC)、低云云量和云降水率(第二类间接作用)。

1.2.2 对流层臭氧(O3)

O3全球平均大气寿命为(23.4± 2.2)天[2], 浓度和辐射强迫的时空季节差异大, 是仅次于CO2和CH4的第三大温室效应辐射强迫源。O3是CO, NOx, NMVOCs和CH4等前体物经一系列光化学反应生成的二次污染物。O3浓度与悬浮颗粒物浓度、土地利用方式、各种燃料和有机涂料的大量使用及湿度和日照等有关[23, 24]。工业化以来, 38%对流层O3的增加与人类相关。过去百年近地面O3浓度增加速率为~0.3%-2%/年, 1750— 2000年对流层O3增加35%, 至2100年浓度将增加1倍[3, 25]; 对流层O3全球年均含量为(337± 23)Tg, 不同模式结果差异10%左右。相同气象条件下工业发达区增幅更大, 夏季尤其显著[26]。

对流层O3对辐射的吸收改变地气系统的辐射收支(表2), 2/3的辐射强迫归因于20世纪大气CH4浓度的增长[5]。工业时代至2005年对全球增温的贡献为0.1~0.4 ° C(CO2为1.3 ° C)。对流层辐射能量的输入会影响O3含量, O3加倍产生的辐射强迫+1.462 W/m2是CO2加倍效应的1/3, 使无反馈的地表增温0.37 ° C [27]。1750— 2000年对流层O3引起的辐射强迫变化为(0.35± 0.15)W/m2(Hanse的计算结果为(0.5± 0.2)W/m2)[2, 28]。平流层O3含量是对流层的8~10倍, 按相同百分率减少(增加), 后者产生的对流层净辐射冷却(增温)效应是前者的2~3倍[29]。

表2 对流层O3变化引起的热辐射冷却[30](单位：W/m2) Table 2 Thermal radiation cooling due to change of ozone concentration[30](unit：W/m2)

O3的大气光化学过程改变多种温室气体和痕量气体的时空分布, 与背景环流及地气系统相互作用影响天气和气候; 含量变化引起南北半球温度梯度倾斜, 影响亚洲季风和对流层降水; 对流层上部和平流层底部O3浓度的变化对气候影响最大, 变化高度影响效应的大小。O3是对流层大气化学过程的强氧化剂, 浓度分布及变化直接影响大气化学循环与平衡和对流层热平衡。过量O3构成环境污染物, 危害人类健康和生态系统, 降低粮食产量和植物吸收CO2的能力, 影响CO2的辐射强迫[31~33]。

1.2.3 甲烷(CH4)

甲烷(CH4)大气平均寿命为9.1~12年[1], GWP100约是CO2的25倍[34]。60%~70%的CH4来自人类活动。湿地是最大的自然源, 其他的来自动植物和海洋 [3, 35]; 气候变暖在某种程度上也促进CH4排放。亚洲, 非洲, 欧洲, 北美, 拉丁美洲和中东等CH4排放量较大。CH4地表混合率比工业革命前增加了近150%, 预计2100年再翻1倍[36]。冰芯记录与大气测量揭示, 对流层CH4背景值从200年前的0.8 cm3/m3增加到目前1.8 cm3/m3, 高于过去65万年[37, 38]。1980s之后CH4引起18%~20%的温室效应, 成为第二大辐射强迫温室气体[2]。2008年+0.50 W/m2, 是LLGHG总辐射强迫的18.2%[34]。持续排放每单位CH4引起20年和100年的STRE分别为52~92和29~63[39]。

南极冰核中16万年密闭气体的CH4含量显示了与气温极好的相关性[40]。CH4强烈吸收地球长波辐射直接产生气候效应。与OH基的化学反应, 一方面增加平流层水汽和对流层O3, 氧化为CO2加剧温室效应, 同时改变自身的寿命和强迫; 另一方面向平流层输送更多O3消耗气体。CH4在高空经紫外线照射分解, 破坏大气化学反应平衡, 危害人类和生态系统。CH4通过影响硫酸盐气溶胶、HFCs和HCFCs产生间接气候效应[41~43]。

1.2.4. 氢氟碳化物(HFCs)

HFCs是CFCs和HCFCs等臭氧消耗物质的替代品, 具有高挥发性和低水溶性, 加权平均寿命15年, 不同HFC物质大气寿命和气候效应不同。2006— 2010的HFC-134a年增加率为10%[4]。2011年HFCs排放量为0.6Gt CO2eq; 2009— 2010年美国HFCs排放量增加9%, 远超CO2增长比例(3.6%)[44]; 截至2020年, 全球HFCs年均排放增加率将在10%~15%的基础上翻倍 [45, 46]。2050年HFCs可引起20%的气候污染, 产生的强迫和增温为CO2的19%, 消耗量超过CFCs在1980s的峰值, 缺乏管制体系的亚洲更严重[47]。HFCs已被列入《京都议定书》的目标温室气体。

HFCs的红外吸收能力与CFCs和HCFCs大致相同, 吸收地球辐射能量的效率比CO2高数千倍, 持续影响地气系统的辐射平衡。HFCs直接辐射强迫(0.019 W/m2)不到LLGHG总辐射强迫的0.1%, 但缺乏严格的排放管制, 该值将从2010年的0.012 W/m2增长至2050年的0.4 W/m2, 相当于CO2强迫增加值的30%~40%[5]。某些HFCs在低层大气中发生光降解, 促进对流层光化学氧化物的生成, 将OH基转化成羟基[48, 49]。

1.3 SLCPs减排措施

直接减排或光催化反应等均能减少污染物, 吸收性气溶胶的减排速率高于散射性气溶胶才能产生双赢的效果。①SLCPs减排措施主要集中在工农业、交通运输和居民生活中, 船舶交通也是公认的重要SLCPs源。BC和CH4分别减排38%和77%, 增温潜能减小90%[91]。减少燃烧产生的颗粒是降低BC最有效的措施：柴油机动车安装颗粒过滤装置、取缔高排放和重污染的车辆; 现代管理体制砖窑和炼焦炉的兴建; 禁止农业残余物等的露天燃烧; 煤砖和清洁能源代替原煤、提供全球通用的现代加热和烹饪方式等。CH4的减排成本明显低于治理其气候效应的成本：回收和减少煤油气开采输送过程CH4的排放泄露; 控制城市垃圾填埋、家畜肥料堆积及废水处理等产生的CH4; 对持续淹水的稻田连续曝气等。②减少对流层O3最主要的措施就是减少其前体物(尤其是CH4); HFCs是人工合成物质, 只能在蒙特利尔条约体系下调控生产、使用和消耗, 降低GWP。

2 研究进展

LLGHG研究主要应用气候变化评估模式, 将排放量转换为浓度计算辐射强迫[50]。SLCPs排放区域变化大, 历史排放资料缺乏, 观测主要利用色谱分析和卫星资料反演等, 同时借助综合的三维化学— 气溶胶— 气候模式, 基于排放清单, 模拟不同排放源和大气化学过程中SLCPs的输送及三维或四维分布, 从而驱动辐射传输或气候模式得到光学特性(如光学厚度)和辐射强迫, 进一步分析各种机制产生的直接和间接气候效应及减排效应(表3)。常用的指标有辐射强迫、GWP和温变潜能(GTP)、特定强迫脉冲 (Specific Forcing Pulse, SFP)和STRE等。

表3 2030年末SLCPs减排引起的全球年均辐射强迫变化[51] Table 3 Global annual radiative forcing change (mW/m2) at the end of reduced emissions (2030) for SLCPs[51]
2.1 BC气溶胶

1950s伦敦烟雾事件和1980s“ 核冬天” 问题开启了BC观测和气候效应研究历史。BC与其他气溶胶共同排放, 混合方式影响BC大气寿命、云作用及光学性质。从一维简单辐射模式到融合云在内的全球三维模式, 定量综合分析BC位于云上、云内和云下时产生的辐射强迫变化[3](表4)。经济评价指标和OC/BC率等专用指标的建立, 更精确的描述BC净气候效应。CCM3, GCM, Goddard, ECHAM5和UCLA等大气环流等模式, 分析BC影响云量和地表反照率的机理, 揭示BC气溶胶本身及与其他气溶胶的混合如何改变地表温度、降水量和赤道辐合带的南北移动等[52~55]。BC引起空气加热不均(对柱温的影响大于地面温度), 影响蒸发、潜热、大气稳定度和对流强度, 干扰大尺度环流、水循环和季风活动。北半球夏季增强的哈德雷环流部分归因于BC和对流层O3的增加; 清除大气中化石燃料燃烧产生的BC和有机物, 5年内全球增温净值将减少20%, 等量于CO2减排1/3后50~200年后的效应[56]。BC导致季风雨季的提前爆发和雨带移动, 影响中国近几十年“ 南涝北旱” 的降水趋势, 减少非洲及印度季风区近50年的降水量[57~62]。全球主要雪冰区、中纬度地区和部分城市开展的BC时空分布研究, 运用GATOR-GCMOM、GISSME和CAM/SNICAR等模拟积雪中BC的变化过程、对反照率的影响及辐射强迫变化。BC雪冰效应导致20世纪20%的北极变暖和冰雪损失。ACCMIP多模式计划评估了BC冰雪效应的全球辐射强迫年代际的变化, BC是20世纪气候的主要人为强迫因素[63~65]。

表4 1750— 2005年BC辐射强迫分类[16] Table 4 Black carbon climate forcing terms, evaluated for industrial era (1750-2005) [16]
2.2 对流层O3

对流层O3的研究始于1960s, 主要涉及O3前体物、O3时空分布特征、光化学路径及大气氧化性、与气溶胶的异相光化学反应、辐射特性及气候环境效应等问题。一般结合野外观测(如ABLE, MLOPEX和PEM-West A等)、实验室烟雾箱和计算机模拟(全球尺度和非均相化学模式等)进行。城区及下风向和生物量燃烧区对流层O3浓度明显偏高。对流层O3产生的经典理论、经验巴斯曲线对前体物的观测和NMHC在内的光化学反应机理的提出最早解释了对流层O3的形成。CH4与OH作用生成CO, 经光化学反应进而形成O3, O3与CO垂直浓度呈线性正相关, 与NOx非线性相关。液相化学反应及与气溶胶的作用, 减少O3前体物, 降低大气颗粒物浓度, 2000年气溶胶表面直接异相反应减少了5%的全球对流层O3[66~70]。从一维到三维的化学— 辐射传输— 气候耦合模式和遥感及空间资料的结合拓宽了研究领域：研究O3的大气化学过程和气溶胶— O3相互作用过程如何改变辐射强迫和引起温带环流变化等; 揭示含量变化引起的对流层和平流层温度变化, 直接和间接的气候效应及敏感性; 分析O3及前体物时空分布的变化、收支和输送机制等。ACCMIP多模式计划评估对流层O3的辐射强迫(0.4± 0.2 W/m2)及遥感数据对模拟结果的订正等使研究有了新的进展[71~75]。

2.3 CH4

1940s通过太阳红外光谱发现了大气CH4的存在及垂直分布[76]; 近1/5人类活动引起的全球变暖归因于CH4(表5), 2030年该值将达50%。稳定温室气体的浓度, 全球CO2和CH4排放分别需减少> 60%和10%; CH4减排缓解海平面上升的效应最大, 其次是CO2, BC和HFCs。NOAA/ESRL/GMD等网络以高精度原位测量分析CH4的混合率; 卫星时空覆盖范围广(如Envisat, GOSAT, ADEOS和MODIS), 利用近红外和热红外等反演定量计算全球源汇, 提供全球CH4含量及时空分布变化[77]。GEOS-Chem和CTM等全球三维化学传输模式可定量评估不同源和区域排放的CH4, 研究当地排放和远距离输送的CH4的差异及影响, 分析CH4浓度分布[78, 79]。CH4排放增加比通过大气化学的间接效应引起的强迫更大, CH4含量在过去2000— 3000年维持在0.6~0.7 cm3/m3, 最近25年激增30%, 目前全球排放量为5.35× 108t/a(410~660 Tg/a)[34, 80]。CH4当前含量为1.803 cm3/m3, 背景对流层浓度1.76 μ L/L。2030年人为CH4排放量在2005年基础上增加25%, 达8586 MtCO2eq。2050年对流层CH4本底含量将达2.1 ppmv[5, 11, 81]。大气CH4含量增加的70%归因于排放源增长, 30%与OH基的减少有关[82]。2007年之后全球CH4出现抬升趋势, 与两极冻土和海冰融化释放CH4密切相关[83]。大气中高浓度的CH4影响其他气体的分解能力, 提供约50%对流层O3的增加, 是21世纪O3变化的主要驱动因子。极地冰芯大气成分等记录证实CH4浓度的长期变化可能与人类活动更相关[2]。

表5 不同研究计算的CH4平均百年增温潜能GWP[84] Table5 The GWP100of CH4 in different studies [84]
2.4 HFCs

HFCs辐射效率为0.02~0.4 W/m2/ppbv, 远超过CO2(0.000014 W/m2/ppbv)、CH4(0.00037 W/m2/ppbv)和N2O (0.00303 W/m2/ppbv)。HFCs大气含量猛增, 与人类活动密切相关, 主要来自发达国家, 但未来排放预测主要来自发展中国家[85, 86]。若以8%年增率增加, 截止2050年HFCs产生的气候效应将取代其作为臭氧消耗替代品的效应。欧洲和北美已经开始利用自然制冷剂(如碳氢化合物和NH3等)替代HFCs。HFCs的大气测量一般采用色谱分析, 当排放大于消耗时, 北半球偏远地区的HFCs要高于南半球, 后者的浓度至少比前者滞后一年; 预计2050s HFCs的全球排放量将达CO2的19%。HFC-134a使用最多且大气含量最大, 美国NOAA的观测点测得HFC-134a含量比偏远地区高出6倍左右。2007年世界气象组织(WMO)报告指出, Cape Grim 地区HFC-125的浓度呈26%/a的指数增率。发展中国家也进行了HFCs平均浓度观测, 如中国城市HFCs浓度比非城区高1.9倍[81]。碳-辐射能量平衡模式可以联系不同HFCs排放情景下的浓度和引起的辐射强迫变化, 结合碳-地球化学模式, 通过能量平衡以评估引起的气候变化和产生的气候效应。HFCs的气候效应与HFC种类密切有关(表6), 若未来几十年HFCs的GWP与目前相当, 2050年引起的辐射强迫可能增加量为CO2的7%~16%(2011年为0.6%)[86, 87]; 若未来HFCs的GWP小于当前值, 则辐射强迫增加值也会相应较低。欧盟(EU)已下令自2017年起禁止移动空调应用GWP> 150的HFCs。

表6 典型HFCs的大气寿命、辐射效率及全球增温潜能[2] Table 6 Life, radiative forcing and GWP of typical HFCs [2]
3 展望
3.1 BC气溶胶

BC研究涉及碳循环、大气环流、光化学反应、与活性气体及气溶胶相互作用等。BC源汇多变(影响吸收特性), 时空分布不均, 排放清除速率及云作用不明确等, 使大气寿命及输送、辐射强迫及气候效应评估等不确定性较大, 因此需要精确的BC排放清单和光学参数(如光学厚度、单次散射率), 了解沉降机理、BC共排物的性质及相互混合方式(引起的云效应和净辐射)、考虑与温室气体吸收带的重叠等。BC的间接效应及吸收性半直接效应、雪冰— 反照率效应、云凝结核和冰核效应、与混合相及冰云的作用亟需深入研究, 模式及参数化方案的完善都亟待遥感和观测数据的支持。

3.2 对流层O3

工业革命之前观测资料的缺乏限制趋势(尤其是柱浓度)的预估。对流层O3及辐射强迫的时空变化、前体物的源解析, 与平流层O3及气溶胶的作用和非均相反应、光化学烟雾及雾霾的形成机理和化学作用等, 都需要建立完善的化学— 辐射— 动力— 气候模式, 并结合空间遥感和实测数据进行精确的评估。

3.3 CH4

大气CH4浓度的快速增加— 缓滞— 回升的异常现象备受争议, 对CH4的源汇、输送、转化和反应机制等的认识不明确, 如何利用大气化学气候模式模拟CH4的化学反应和输送, 预测浓度变化趋势, 源清单调查及排放产生的气候效应等都深入探究。

3.4 HFCs

HFCs消耗量逐年增加, 较高的增温潜能使其成为《京都议定书》目标限排温室气体, 需要综合考虑直接和间接气候效应之间的均衡, 协调各种HFC物质的使用比或寻求替代品以降低增温潜能。

The authors have declared that no competing interests exist.

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