Abstract:
With continuous endeavors to control air pollutant emissions, the average concentration of PM2.5 in Shanghai in 2019-2020 satisfied the national secondary standard (35 μg m-3) for the first time. In this study, the two-year dataset of hourly resolution PM2.5 compositions observed in downtown Shanghai was used to investigate the relative contribution of sulfate and nitrate as well as particulate acidity. The average concentration of SO2 was reduced to 7.7 μg m-3, while the concentration of NOx remained above 40 μg m-3, indicating that the control of SO2 was more effective than that of NOx during the 13th Five-Year Plan period. Thus, the sulfate pollution was significantly reduced whereas the nitrate loading remained almost constant. The monthly N/S ratio varied from below 0.6 to above 2.0, indicating that the contribution of automobile exhaust to PM2.5 is seasonally dependent. Contrary to sulfate, the nitrate fraction increased rapidly with the increase of PM2.5 mass, suggesting that the explosive growth of nitrate has become a major driver of haze formation. ISORROPIA simulations show that PM2.5 was moderately acidic with pH values following the trend of winter > spring > autumn > summer. The diurnal variation of nitrate was related to the changes in aerosol water content, indicating the effect of heterogeneous aqueous reactions on secondary aerosol formation. The effectiveness of emission control for reducing inorganic PM2.5 varied with different gas precursors and seasons. The abatement of NH3 emissions will increase particle acidity and acid rain pollution, although it is more effective than that of NOx when the emission reduction is larger than 60%. This study suggests that the control of vehicle exhaust should be given priority in the Yangtze River Delta for coordinately mitigating PM2.5 and acid rain pollution.
摘要:
不断努力控制大气污染物排放,2019-2020年上海市PM2.5平均浓度首次达到国家二级标准(35μgm-3)。在这项研究中,在上海市中心观察到的每小时分辨率PM2.5组成的两年数据集用于调查硫酸盐和硝酸盐以及颗粒酸度的相对贡献。SO2的平均浓度降至7.7μgm-3,而NOx的浓度保持在40μgm-3以上,表明“十三五”期间SO2的控制比NOx的控制更为有效。因此,硫酸盐污染显着减少,而硝酸盐负荷几乎保持恒定。每月的N/S比从低于0.6到高于2.0变化,表明汽车尾气对PM2.5的贡献取决于季节。与硫酸盐相反,硝酸盐含量随着PM2.5质量的增加而迅速增加,这表明硝酸盐的爆炸性增长已成为雾霾形成的主要驱动力。isorropia模拟表明,PM2.5呈中等酸性,pH值遵循冬季>春季>秋季>夏季的趋势。硝酸盐的日变化与气溶胶含水量的变化有关,表明非均相水性反应对二次气溶胶形成的影响。排放控制对减少无机PM2.5的有效性因气体前体和季节的不同而不同。减少NH3排放将增加颗粒酸度和酸雨污染,尽管当减排量大于60%时,它比NOx更有效。本研究表明,长三角地区应优先控制汽车尾气,以协调缓解PM2.5和酸雨污染。