Rapid transition in winter aerosol composition in Beijing from 2014 to 2017: response to clean air actions

Abstract

<p><strong>Abstract.</strong> The clean air actions implemented by the Chinese government in 2013 have led to significantly improved air quality in Beijing. In this work, we combined the in-situ measurements of the chemical components of submicron particles (PM<sub>1</sub>) in Beijing during the winters of 2014 and 2017 and a regional chemical transport model to investigate the impact of clean air actions on aerosol chemistry and quantify the relative contributions of anthropogenic emissions, meteorological conditions, and regional transport to the changes in aerosol chemical composition from 2014 to 2017. We found that the average PM<sub>1</sub> concentration in winter in Beijing decreased by 49.5 % from 2014 to 2017 (from 66.2 μg m<sup>−3</sup> to 33.4 μg m<sup>−3</sup>). Sulfate exhibited a much larger decline than nitrate and ammonium, which led to a rapid transition from sulfate-driven to nitrate-driven aerosol pollution during the wintertime. Organic aerosol (OA), especially coal combustion OA, and black carbon also showed large decreasing rates, indicating the effective emission control of coal combustion and biomass burning. The decreased sulfate contribution and increased nitrate fraction were highly consistent with the much faster emission reductions in sulfur dioxide (SO<sub>2</sub>) due to phasing out coal in Beijing compared to reduction in nitrogen oxides emissions estimated by bottom-up inventory. The chemical transport model simulations with these emission estimates reproduced the relative changes in aerosol composition and suggested that the reduced emissions in Beijing and its surrounding regions played a dominant role. The variations in meteorological conditions and regional transport contributed much less to the changes in aerosol concentration and its chemical composition during 2014–2017 compared to the decreasing emissions. Finally, we observed that changes in precursor emissions also altered the aerosol formation mechanisms. The decreased SO<sub>2</sub> emissions suppressed the rapid formation of secondary sulfate through heterogeneous reactions. The observed explosive growth of sulfate at a relative humidity (RH) greater than 50 % in 2014 was delayed to a higher RH of 70 % in 2017. Thermodynamic simulations showed that the decreased sulfate and nitrate concentrations have lowered the aerosol water content, particle acidity, and ammonium particle fraction. The results in this study demonstrated the response of aerosol chemistry to the stringent clean air actions and identified that the anthropogenic emission reductions are a major driver, which could help to further guide air pollution control strategies in China.</p>

Drivers of improved PM 2.5 air quality in China from 2013 to 2017

“…S17 and refs. 39–41). Future actions focusing on NO x abatements from on-road diesel vehicles and off-road gas vehicles (42) and NH 3 abatements in the agriculture sector should be implemented.…”

Response of major air pollutants to COVID-19 lockdowns in China

“…The formation of tropospheric ozone is relatively complex, influenced on the one hand by solar radiation and on the other by the concentration of other atmospheric pollutants ( Wang et al, 2017 ). In recent years, there has been a general decrease in PM 2.5 in China's major cities ( Ding et al, 2019 ; Li et al, 2019 ; Zhang et al, 2019 ), but a certain increase in tropospheric O 3 ( Chan et al, 2017 ; Chan et al, 2018 ; Wang et al, 2020b ). PM 2.5 has a very large impact on visibility and is therefore more likely to be of public concern.…”

Seasonal variations in the high time-resolved aerosol composition, sources, and chemical process of background submicron particles in North China Plain

“…The formation mechanisms of particulate pollution are complex because of the unfavorable meteorological conditions, complex source emissions, and 40 geographical conditions. For example, sulfate dominated the secondary inorganic aerosols in industrialized cities located in the south of the NCP, while in recent years, nitrate dominated the secondary inorganic aerosols in the north of the NCP (Huang et al, 2018;Li et al, 2019a). High relative humidity (RH) favored heterogeneous reactions and hygroscopic growth, leading to an increase in secondary aerosols and further aggravating haze pollution in the NCP (Sun et al, 2013a;Liu et al, 2016).…”