Mutual promotion between aerosol particle liquid water and particulate nitrate enhancement leads to severe nitrate-dominated particulate matter pollution and low visibility

Abstract

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 (pNO3-) over the NCP. In this study, we observed a polluted episode with the particulate nitrate mass fraction in nonrefractory PM1 (NR-PM1) being up to 44 % during wintertime in Beijing. Based on this typical pNO3--dominated haze event, the linkage between aerosol water uptake and pNO3- 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 pNO3- 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.

Rapid mass growth and enhanced light extinction of atmospheric aerosols during the heating season haze episodes in Beijing revealed by aerosol-chemistry-radiation-boundary layer interaction

“…LT) measurement data from October 2018 to February 2019 were selected for further analysis. As shown by Figure 3 and consistent with other observations in Beijing (Tang et al, 2016;Wang et al, 2020c), there was a general tendency for the PM2.5 mass concentration to increase with a decreasing MLH. Organic compounds and nitrate were the most abundant fractions of the daytime aerosol mass composition, contributing together approximately 70% to total NR-PM2.5 mass concentration.…”

Tropospheric aerosol hygroscopicity in China

“…In addition, a few studies investigated aerosol hygroscopic growth and CCN activities concurrently, and both consistencies (Wu et al, 2017;Zhang et al, 2017; and discrepancies (Ma et al, 2016; were reported. The discrepancies could be caused by several factors (Petters and Kreidenweis, 2008;Wex et al, 2009;Petters and Kreidenweis, 2013;, such as solution non-ideality of aerosol droplets, limited solubility of some components contained by aerosol particles, surface tension effects, liquid-liquid phase separation, etc.…”

Effectiveness of emission control in reducing PM<sub>2.5</sub> pollution in central China during winter haze episodes under various potential synoptic controls

“…The contribution of emission sources has been widely recognized as the decisive factor of PM 2.5 pollution over urban agglomerations, including industrial exhaust, urban transportation, residential emission, power plants, agricultural activities, and bio-combustion (Huang et al, 2014;Tian et al, 2016;Wu et al, 2018;An et al, 2019). The outbreak, persistence, and dissipation of particle pollution generally depends on meteorological conditions and regional synoptic patterns controlled by the large-scale or synoptic-scale atmospheric circulation (Chuang et al, 2008;Zhang et al, 2012;Russo et al, 2014;Zheng et al, 2015;Shu et al, 2017;Li et al, 2019).…”

“…port hub with sub-basin topography, central China is a region of transmission pollution characteristics affected by two reported transport pathways from the vast flatland in central eastern China (Yu et al, 2020) and from the NCP region (H. . In combination with high anthropogenic emissions (Wu et al, 2018) and secondary aerosol formation (Huang et al, 2020), central China often suffers severe pollution episodes in winter caused by PM 2.5 (Gong et al, 2015;Xu et al, 2017). In this study, we conduct a circulation classification to differentiate the synoptic modes during the severe particle pollution episodes in winter over central China from 2013 to 2018 by using the Lamb-Jenkinson method.…”