Insights into aerosol chemistry during the 2015 China Victory Day parade: results from simultaneous measurements at ground level and 260 m in Beijing

摘要

Strict emission controls were implemented in Beijing and adjacentprovinces to ensure good air quality during the 2015 China Victory Dayparade. Here, we conducted synchronous measurements of submicron aerosols(PM) at ground level and 260 m on a meteorological tower by using ahigh-resolution aerosol mass spectrometer and an aerosol chemical speciationmonitor, respectively, in Beijing from 22 August to 30 September. Ourresults showed that the average PM concentrations are 19.3 and 14.8 µg m at ground level and 260 m, respectively, during thecontrol period (20 August–3 September), which are 57 and 50 % lowerthan those after the control period (4–30 September). Organic aerosols(OAs) dominated PM during the control period at both ground level and260 m (55 and 53 %, respectively), while their contribution showedsubstantial decreases (∼  40 %) associated with an increasein secondary inorganic aerosols (SIAs) after the parade, indicating a largerimpact of emission controls on SIA than OA. Positive matrix factorization ofOA further illustrated that primary OA (POA) showed similar decreases assecondary OA (SOA) at both ground level (40 % vs. 42 %) and 260 m(35 % vs. 36 %). However, we also observed significant changes in SOAcomposition at ground level. While the more oxidized SOA showed a large decrease by 75 %,the less oxidized SOA was comparable during (5.6 µg m) andafter the control periods (6.5 µg m). Our results demonstratedthat the changes in meteorological conditions and PM loadings have affectedSOA formation mechanisms, and the photochemical production of fresh SOA wasmore important during the control period. By isolating the influences ofmeteorological conditions and footprint regions in polluted episodes, wefound that regional emission controls on average reduced PM levels by 44–45 %, and the reductions were close among SIA, SOA and POA at 260 m,whereas primary species showed relatively more reductions (55–67 %)than secondary aerosol species (33–44 %) at ground level.