Mutual promotion between aerosol particle liquid water and particulate nitrate enhancement leads to severe nitrate-dominated particulate matter pollution and low visibility
Mutual promotion between aerosol particle liquid water and particulate nitrate enhancement leads to severe nitrate-dominated particulate matter pollution and low visibility
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DOI：
10.5194/acp-20-2161-2020
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发表时间：
2020-02
影响因子：
6.3
通讯作者：
Yu Wang
中科院分区：
文献类型：
--
作者：
Yu Wang
抽象的。与北美和西欧的情况一样，近年来华北平原（NCP）的SO2排放量大幅减少。SO2和NOx浓度的不同还原速率导致NCP上经常发生以硝酸盐（p NO3-）为主的颗粒物污染。在这项研究中，我们观察到一个污染事件的颗粒硝酸盐的质量分数在非难降解PM 1（NR-PM 1）是高达44%，在北京的冬季。以这次典型的pNO 3 -主导的灰霾天气为例，通过现场观测和理论计算，研究了气溶胶水分吸收与pNO 3 -增强之间的联系，进而影响能见度的下降。在灰霾发展期间，随着环境相对湿度（RH）从10%增加到70%，气溶胶粒子液态水从开始时的101 µg m−3增加到灰霾完全发展期间的1075 µg m−3。气溶胶液态水进一步增加了气溶胶的表面积和体积，增强了N2 O 5在颗粒上的冷凝损失。从开始到完全发展的阴霾，N2 O 5的冷凝损失增加了一个因素的20时，只考虑气溶胶表面积和体积的干颗粒，而增加了一个因素的25时，考虑额外的表面积和体积由于吸水。在HNO 3和NH3过饱和的条件下，气溶胶中的液态水有利于HNO 3在颗粒相中的热力学平衡。上述结果表明，在灰霾发生过程中，随着环境相对湿度的升高，气溶胶对水的吸收增强了pNO 3 -，由于硝酸盐颗粒的吸湿性，促进了气溶胶对水的吸收。气溶胶粒子、液态水和硝酸盐粒子的相互促进作用可使大气质量迅速下降，能见度在1d内减半。还原含氮气体前体，例如，通过控制交通排放，对减轻北控区严重雾霾事件至关重要。
Abstract. As has been the case in North America and western Europe, the SO2 emissions have substantially reduced in the North China Plain (NCP) in recent years. Differential rates of reduction in SO2 and NOx concentrations result in the frequent occurrence of particulate matter pollution dominated by nitrate ( p NO 3 - ) over the NCP. In this study, we observed a polluted episode with the particulate nitrate mass fraction in nonrefractory PM 1 (NR-PM 1 ) being up to 44 % during wintertime in Beijing. Based on this typical p NO 3 - -dominated haze event, the linkage between aerosol water uptake and p NO 3 - enhancement, further impacting on visibility degradation, has been investigated based on field observations and theoretical calculations. During haze development, as ambient relative humidity (RH) increased from ∼10 % to 70 %, the aerosol particle liquid water increased from ∼1 µg m−3 at the beginning to ∼75 µg m−3 in the fully developed haze period. The aerosol liquid water further increased the aerosol surface area and volume, enhancing the condensational loss of N2O5 over particles. From the beginning to the fully developed haze, the condensational loss of N2O5 increased by a factor of 20 when only considering aerosol surface area and volume of dry particles, while increasing by a factor of 25 when considering extra surface area and volume due to water uptake. Furthermore, aerosol liquid water favored the thermodynamic equilibrium of HNO3 in the particle phase under the supersaturated HNO3 and NH3 in the atmosphere. All the above results demonstrated that p NO 3 - is enhanced by aerosol water uptake with elevated ambient RH during haze development, in turn facilitating the aerosol take-up of water due to the hygroscopicity of particulate nitrate salt. Such mutual promotion between aerosol particle liquid water and particulate nitrate enhancement can rapidly degrade air quality and halve visibility within 1 d. Reduction of nitrogen-containing gaseous precursors, e.g., by control of traffic emissions, is essential in mitigating severe haze events in the NCP.