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Condensable particulate matter (CPM) emitted from stationary combustion and mobile sources exhibits high emissions and a large proportion of organic components. However, CPM is not generally measured when conducting emission surveys of PM in most countries, including China. Consequently, previous emission inventories have not included emission rates for CPM. Here, we construct an emission inventory of CPM in China with a focus on organic aerosols (OAs) based on collected CPM emission information. Results show that OA emissions are enhanced twofold after the inclusion of CPM in a new inventory for China for the years 2014 and 2017. Considering organic CPM emissions and model representations of secondary OA (SOA) formation from CPM, a series of sensitivity cases have been simulated here using the three-dimensional Community Multiscale Air Quality (CMAQ) model to estimate the contributions of CPM emissions to atmospheric OA and fine PM (PM 2.5 , particulate matter with aerodynamic diameter not exceeding 2.5 µ m) concentrations in China. Compared with observations at a Beijing site during a haze episode from 14 October to 14 November 2014, estimates of the temporal average primary OA (POA) and SOA concentrations were greatly improved after including the CPM effects. These scenarios demonstrated the significant contributions of CPM emissions from stationary combustion and mobile sources to the POA (51 %–85 %​​​​​​​), SOA (42 %–58 %), and total OA concentrations (45 %–75 %). Furthermore, the contributions of CPM emissions to total OA concentrations were demonstrated over the 2 major cities and 26 other cities of the Beijing–Tianjin–Hebei region (hereafter referred to as the "BTH2 + 26 cities") in December 2018, with average contributions of up to 49 %, 53 %, 54 %, and 50 % for Handan, Shijiazhuang, Xingtai, and Dezhou, respectively. Correspondingly, the inclusion of CPM emissions also narrowed the gap between simulated and observed PM 2.5 concentrations over the BTH2 + 26 cities. These results improve the simulation performance of atmospheric OA and PM 2.5 and may also provide important implications for the sources of OA. [ABSTRACT FROM AUTHOR]

The downward transport of ozone (O 3) stemming from the stratosphere-to-troposphere exchange (STE) can be a significant contributor to background O 3. Such enhancement of background O 3 may also influence ground-level PM 2.5 , particularly in polluted regions which have abundant precursor emissions. In this study, we quantified the STE impact on tropospheric O 3 and its subsequent influence on surface PM 2.5 across the northern hemisphere. The sensitivity analyses was conducted by using a comprehensive hemispheric atmospheric modeling system. Results suggest the surface PM 2.5 concentration can be considerably enhanced by the STE in polluted regions including East China, East US, and Europe, mostly in winter and spring. In winter, the PM 2.5 concentrations in East China, East US, and Europe are estimated to be enhanced by 1.3%, 3.5% and 5.5% due to the STE. The STE-enhanced PM 2.5 concentrations are typically higher on high pollution days suggesting likely increasing contributions in regions with the growing pollution levels. During the heavy polluted days, the PM 2.5 concentrations in East China can be enhanced by 2.289 μg/m3 in winter and 2.034 μg/m3 in spring due to the STE. The STE-enhanced PM 2.5 also exhibits strong diurnal variations following a pattern similar to the total PM 2.5 concentration, with high increasing ratio in the morning and low at afternoon, suggesting that the enhancement is most pronounced during peak pollution events. The STE-enhanced PM 2.5 is exclusively contributed by the increase of nitrate, ammonium, and secondary organic aerosol which in-turn are strongly influenced by the atmospheric oxidation capacity. • STE-driven O 3 downward transport can lead to non-trivial enhancement of surface PM 2.5 • STE-enhanced PM 2.5 is most pronounced in polluted regions. • STE enhances peak PM 2.5 thereby further exacerbating high pollution levels. • STE-enhanced PM 2.5 is exclusively caused by an increase of secondary aerosols. • STE enhancement on SOA becomes more important during heavier polluted period. [ABSTRACT FROM AUTHOR]