Secondary organic aerosol enhanced by increasing atmospheric oxidizing capacity in Beijing–Tianjin–Hebei (BTH), China

Tian Feng, Shuyu Zhao, Naifang Bei, Jiarui Wu, Suixin Liu, Xia Li, Lang Liu, Yang Qian, Qingchuan Yang, Yichen Wang, Weijian Zhou, Junji Cao (+1 others)
2019 Atmospheric Chemistry and Physics  
<p><strong>Abstract.</strong> The implementation of the Air Pollution Prevention and Control Action Plan in China since 2013 has profoundly altered the ambient pollutants in the Beijing–Tianjin–Hebei (BTH) region. Here we show observations of substantially increased <span class="inline-formula">O<sub>3</sub></span> concentrations (about 30&amp;thinsp;%) and a remarkable increase in the ratio of organic carbon (OC) to elemental carbon (EC) in BTH during the autumn from 2013 to 2015, revealing an
more » ... 2015, revealing an enhancement in atmospheric oxidizing capacity (AOC) and secondary organic aerosol (SOA) formation. To explore the impacts of increasing AOC on the SOA formation, a severe air pollution episode from 3 to 8 October 2015 with high <span class="inline-formula">O<sub>3</sub></span> and PM<span class="inline-formula"><sub>2.5</sub></span> concentrations is simulated using the WRF-Chem model. The model performs reasonably well in simulating the spatial distributions of PM<span class="inline-formula"><sub>2.5</sub></span> and <span class="inline-formula">O<sub>3</sub></span> concentrations over BTH and the temporal variations in PM<span class="inline-formula"><sub>2.5</sub></span>, <span class="inline-formula">O<sub>3</sub></span>, <span class="inline-formula">NO<sub>2</sub></span>, OC, and EC concentrations in Beijing compared to measurements. Sensitivity studies show that the change in AOC substantially influences the SOA formation in BTH. A sensitivity case characterized by a 31&amp;thinsp;% <span class="inline-formula">O<sub>3</sub></span> decrease (or 36&amp;thinsp;% OH decrease) reduces the SOA level by about 30&amp;thinsp;% and the SOA fraction in total organic aerosol by 17&amp;thinsp;% (from 0.52 to 0.43, dimensionless). Spatially, the SOA decrease caused by reduced AOC is ubiquitous in BTH, but the spatial relationship between SOA concentrations and the AOC is dependent on the SOA precursor distribution. Studies on SOA formation pathways further show that when the AOC is reduced, the SOA from oxidation and partitioning of semivolatile primary organic aerosol (POA) and co-emitted intermediate volatile organic compounds (IVOCs) decreases remarkably, followed by those from anthropogenic and biogenic volatile organic compounds (VOCs). Meanwhile, the SOA decrease in the irreversible uptake of glyoxal and methylglyoxal on the aerosol surfaces is negligible.</p>
doi:10.5194/acp-19-7429-2019 fatcat:uupduk5grrgexp7mshgweckhrm