Changes in Aerosol Chemistry From 2014 to 2016 in Winter in Beijing: Insights From High‐Resolution Aerosol Mass Spectrometry

Abstract

Air quality has been continuously improved in recent years in Beijing, yet severe haze episodes still frequently occur in winter. Here we deployed an Aerodyne high‐resolution aerosol mass spectrometer in two winter seasons during the same period to investigate the changes in aerosol chemistry from 2014 to 2016 in Beijing. Compared to 2014, submicron aerosol (PM1) species showed ubiquitous increases in mass concentrations by 10–130% in winter 2016, of which nitrate showed the largest increase among all aerosol species leading to a much higher NO3/SO4 ratio in 2016 (1.36 ± 0.90) than 2014 (0.72 ± 0.59). This result highlights an increasing role of nitrate in particulate matter pollution in recent years in Beijing. Aerosol composition and size distributions also changed significantly. Secondary inorganic species showed elevated contributions by ~10% in winter 2016 associated with corresponding decreases in organic aerosol (OA). Positive matrix factorization of OA illustrated the significant changes in both primary emissions and secondary production. While cooking OA decreased substantially from 25% in 2014 to 15% in 2016, the contribution of biomass burning OA slightly increased instead. Although secondary OA contributed similarly to OA in the two winters (49% vs. 53%), we observed ubiquitous increases (~50%) in photochemically related oxygenated OA and oxidized primary OA, and oxygen‐to‐carbon ratios of OA, indicating the enhanced photochemical production in winter 2016. Aqueous‐phase production of secondary OA however was relatively similar in the two winters. Further analysis demonstrated that the changes in aerosol and OA composition varied differently across different pollution and relative humidity levels.

Mutual promotion effect between aerosol particle liquid water and nitrate formation lead to severe nitrate-dominated particulate matter pollution and low visibility

“…With decreasing in PM mass concentration, the mass fraction of particulate nitrate during these haze events in Beijing enhanced substantially. In 2014, the highest fraction of nitrate in PM1 was reported as ~20% and increased to ~35% in 2016 (Xu et al, 2019b), which is comparable to the ratio (44%) in this study. The particulate nitrate became more dominant in secondary inorganic compounds other than particulate sulfate with the air quality improvement over NCP.…”

Urban organic aerosol composition in Eastern China differs from North to South: Molecular insight from a liquid chromatography-Orbitrap mass spectrometry study

“…In the last decades, China has experienced rapid industrialization and urbanization accompanied by severe and persistent particulate air pollution (Huang et al, 2014;Sun et al, 2014;Ding et al, 2016;Song et al, 2018;Shi et al, 2019;Xu et al, 2019). These particulate air pollution extremes can not only influence the regional air quality and human health in China, but also lead to a global environmental problem due to long-distance transport of pollutants.…”

Predominance of secondary organic aerosol to particle-bound reactive oxygen species activity in fine ambient aerosol

“…Other assays measure the ability of PM to deplete biological antioxidants such as ascorbic acid (AA), glutathione, and uric acid (Mudway et al, 2004;Fang et al, 2016). Since the different assays capture different fractions of the oxidant activity of PM, a di-rect comparison of measurements is challenging (Shiraiwa et al, 2017;Fang et al, 2016;Weber et al, 2018;Calas et al, 2018;Perrone et al, 2016;Yang et al, 2014;Janssen et al, 2015). Nonetheless, the ROS generation potential (referred to as oxidative potential, OP) determined using these assays was found to be more strongly associated with emergency department visits for airway and nasal inflammation, asthma, wheezing, and congestive heart failure than PM 2.5 (PM with a particle diameter smaller than 2.5 µm) (Bates et al, 2015;Fang et al, 2016;Janssen et al, 2015).…”