我国雾-霾成因及其治理的思考

Factors contributing to haze and fog in China

通过分析雾和霾与气溶胶的联系、维持机制、污染物构成及如何治理等问题,指出我国现今雾-霾问题的主因是严重的气溶胶污染,但气象条件对其形成、分布、维持与变化的作用显著.二次气溶胶(通常占我国小于10μm气溶胶质量浓度的一半以上)形成与变化受气象条件影响大,导致我国霾呈区域性分布的特点.在我国霾最为严重的华北区域,新粒子形成和老化阶段均有有机气溶胶的贡献,与有机物混合后的气溶胶潮解点提前,吸湿增长因子变小.干气溶胶粒子吸湿增长会使在高相对湿度下观测的PM2.5质量浓度"虚高";有约70%的气溶胶粒子与其他类型气溶胶内混合,高浓度矿物气溶胶与污染气体发生非均相化学反应使更多二次气溶胶形成,也使我国雾-霾问题更为复杂.还发现受气溶胶影响的低云较高云中云滴数多但有效半径小,高浓度气溶胶影响的云雾形成机制明显不同于低污染状况,在低过饱和条件下大量大于150nm粒子活化为云雾凝结核,且化学组成对活化有明显影响.由于我国气溶胶浓度水平在世界范围内较高,仅次于南亚城市,远高于欧洲和美洲的城市与城郊区域,且具有上述变化特点并与云雾的相互作用复杂,导致我国当今的雾和霾都已不是完全的自然现象,人为气溶胶粒子不仅对霾有贡献,还作用于云雾的形成.雾-霾形成后会使到达地面的辐射减少,大气层节稳定度增加,有利于气溶胶不断积聚、凝结和增长,在达到过饱和状况下还产生更多云雾滴,形成"恶性循环"的持续性雾-霾.异常的静稳天气和居高的气溶胶浓度共同造成了2013年1月6～16日我国中东部大范围、持续性雾-霾.对治理雾-霾污染的长期与艰巨性要有充分的科学判断,建议政府对能源结构调整作出抉择,且要不遗余力地对近期可以削减的污染源加大控制力度.污染控制需要区域共同参与,应有国家政策和机制的强力驱动.

We assess the relationship among haze-fog,aerosol and meteorological conditions,and analyze the chemical compositions and sources of aerosol particles,as well make some suggestions for aerosol control strategy.Present-day haze and fog in China are both dependent on atmospheric aerosol loading and weather conditions.The secondary aerosol formation and changes,which dominate the total aerosol mass and are highly influenced by meteorological conditions,characterized the regional haze feature in East China.In the Huabei Plain,which suffers from intense haze and fog,secondary organic aerosols are found to have similar role like sulphate,contributing to aerosol mass during both new particle formation and aging stages.The organic aerosol mix with inorganic ones to form hygroscopic particles earlier at ～70% relative humidity（RH）,but which have a small hygroscopic growth factor.The hygroscopic aerosol particles would also make the PM2.5 mass monitoring at China exhibiting unrealistic high concentration under high RH stage.About 70% of these particles are internally mixed with two or three different aerosol components.Most mineral particles are covered with visible coatings,including fly ash,soot and metal particles,leading to have more secondary aerosol formed on their surface.This complicates haze formation in China.Under high aerosol particle concentrations,greater numbers of cloud droplets with relative small-size are observed in low clouds relative to high clouds;and the associated aerosol impact on cloud microphysical processe is different in less polluted areas.At low supersaturation most of hygroscopic particles larger than 150 nm form cloud condensation nuclei（CCN）,and the impact of aerosol chemical composition on CCN activation is significant.There is a high aerosol concentration in China relative to other areas in the world,except for urban South Asia.These particles form under complex conditions and interact with clouds,resulting that present-day haze and fog in China both are not natural phenomenon.Haze and fog reduces surface radiation,making the atmosphere more stable,resulting in continuous coagulation,condensation,accumulation of aerosol,and more CCN activation,leading to serious and maintained haze-fog events.The heavy and persistent haze-fog between 6 and 16 January 2013 in East China was caused by both high aerosol loading and singular static weather conditions.We need to have adequate scientific judgment on the complexity and expectation of aerosol emission reduction in China.The government needs to make informed decisions and implement laws to maintain the health of its people,but this is not easy when we strive for economic growth.There is no easy solution to control aerosol sources,but the government should spare no effort to cut aerosol and their precursor＇s gas emission.Regional pollution control is also very critical;a strong policy and protocol needs to be enforced by the central government to drive provincial leaders to make the necessary changes to ensure better air quality and quality of life for the population.