Atmospheric Chemical Processes of Secondary Particle Formation in the Winter of North China
Abstract
With the rapid economic growth and large energy consumption, China is suffering severe air pollution. Frequent occurrence of regional PM2.5 and haze pollution events in the North China has attracted much attention worldwide. To improve the air quality, the Chinese government conducted the "Action Plan on Prevention and Control of Air Pollution" during 2013-2017. As the results the annual PM2.5 decreased significantly from 89.5 μg/m3 in 2013 to 58 μg/m3 in 2017 for Beijing case. The gap for the PM2.5 spatial distribution between the north and the south narrowed down. With the effective control of primary air pollutants, the concentration level of air pollutants decreased obviously. However, the difference between atmospheric oxidation and the concentrations of air pollutants will also lead to the change of chemical transformation mechanism. The continuous improvement of air quality requires a full understanding of formation mechanism of secondary air pollution.
The intensive field campaigns were conducted based on the supersites on the major pathways of pollutant transport, i.e. southwest, south, east, and northeast, in the winter of 2017 and 2018. Our results revealed that due to the energy changing from coal to natural gas, both SO2 and particulate sulfate have decreased dramatically. During the pollution episodes secondary organic aerosol (SOA) and nitrate became dominant in particle mass concentrations. The haze formation includes two processes: "seeds" production (efficient nucleation, as well as primary emission) and rapid particle growth. The efficient nucleation is attributed to large emission of precursors, i.e. volatile organic compounds (VOCs) from vehicle emissions. Our study implied that organics play an important role on nucleation and initial growth. More than 80% of the nitrate is formed from gas phase reaction, and while sulfate is mainly from aqueous-phase reaction, i.e. in cloud process, or droplet process. SOA formation is much more complicated. Gas phase reaction is dominant during clean and transit periods. With the increasing of particle pollution, aqueous-phase reaction becomes important due to increasing aerosol liquid water content (ALWC), which is attributed to the increasing of hygroscopic compounds, i.e. nitrate, and sulfate. This presentation will also discuss the interplay between source emissions, atmospheric chemical mechanisms, meteorological conditions and aerosol thermodynamics, which is non-linear and quite complex, but important for effective mitigation strategies.- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2019
- Bibcode:
- 2019AGUFM.A24B..02M
- Keywords:
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- 0305 Aerosols and particles;
- ATMOSPHERIC COMPOSITION AND STRUCTURE;
- 0317 Chemical kinetic and photochemical properties;
- ATMOSPHERIC COMPOSITION AND STRUCTURE;
- 0345 Pollution: urban and regional;
- ATMOSPHERIC COMPOSITION AND STRUCTURE;
- 0365 Troposphere: composition and chemistry;
- ATMOSPHERIC COMPOSITION AND STRUCTURE