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In the autumn of 2019, a 5 d long-lasting dust event was observed using a synergy of field measurement techniques in Shanghai. This particular dust event stood out from others due to its unique characteristics, including low wind speed, high relative humidity, elevated levels of gaseous precursors, and contrasting wind patterns at different altitudes. During this event, three distinct dust stages were identified. The first stage was a typical dust invasion characterized by high concentrations of particulate matters but relatively short duration. In contrast, the second stage exhibited an unusual enhancement of ozone, attributed to compound causes of a weak synoptic system, transport from the ocean, and subsidence of high-altitude ozone downdrafted by dust. Consequently, gas-phase oxidation served as the major formation pathway of sulfate and nitrate. In the third stage of dust, a noteworthy phenomenon known as dust backflow occurred. The dust plume originated from the Shandong Peninsula and slowly drifted over the Yellow Sea and the East China Sea before eventually returning to Shanghai. Evidence of this backflow was found through the enrichment of marine vessel emissions (V and Ni) and increased solubility of calcium. Under the influence of humid oceanic breezes, the formation of nitrate was dominated by aqueous processing. Additionally, parts of nitrate and sulfate were directly transported via sea salts, evidenced by their co-variation with Na + and confirmed through thermodynamic modeling. The uptake of NH 3 on particles, influenced by the contributions of alkali metal ions and aerosol pH, regulated the formation potential of secondary aerosol. By developing an upstream–receptor relationship method, the quantities of transported and secondarily formed aerosol species were separated. This study highlights that the transport pathway of dust, coupled with environmental conditions, can significantly modify the aerosol properties, especially at the complex land–sea interface. [ABSTRACT FROM AUTHOR]

A five-days long-lasting dust event was observed with a synergy of field measurements techniques in Shanghai in the autumn of 2019. Different from most dust events, this dust was an unusual one characterized of low wind speed, high relative humidity, high concentrations of gaseous precursors, and contrasting wind vectors between low and high altitudes. Three dust stages were identified and the first stage was a normal dust invasion with high particulate concentrations and short duration. In contrast, unusual enhancement of ozone was observed in the second stage, due to compound causes of weak synoptic system, transport from the ocean, and subsidence of high-altitude O3 down drafted by dust. As a result, sulfate and nitrate moderately correlated with O3 while had almost no correlation with aerosol liquid water content, indicating the dominant role of gas phase oxidations. During the third stage of dust, a special phenomenon of dust backflow was observed that the dust plume drifted from the Shandong Peninsula and travelled slowly over the Yellow Sea and the East China Sea, finally returning to Shanghai. The dust backflow was evidenced by the enrichment of marine vessel emissions (V and Ni) and increased solubility of calcium. Under the humid oceanic breezes, the formation of nitrate was dominated by aqueous processing, while the strong correlation between SO42- and Na+ suggested that a considerable part of sulfate was aged and directly transported. Based on the thermodynamic modeling, sea salts probably involved more in the secondary aerosol formation than the dust heterogeneous reactions. By developing an upstream-receptor relationship method, the amounts of transported and secondarily formed aerosol species were separated. This study highlights that the transport pathway of dust and environmental conditions could significantly modify the aerosol properties, especially at the complex land-sea interface. [ABSTRACT FROM AUTHOR]

Organic carbon (OC) and elemental carbon (EC) are major chemical constituents of ambient submicron particles (PM 1) and have substantial implications for air quality, climate dynamics, and human health. Long-term observations of daily mean mass concentrations of OC and EC in PM 1 were conducted in Qingdao, a typical coastal megacity in northern China, in autumn and winter from Nov. 2017 to Jan. 2023. The variety in OC and EC concentrations under the active emission reduction policies of long-term carbon reduction in China, combined with the impact of the COVID-19 pandemic, were analyzed. OC and EC concentrations decreased noticeably from 8.28 ± 4.59 μg m−3 and 2.00 ± 1.17 μg m−3 during pre-COVID-19 pandemic to 6.34 ± 3.82 μg m−3 and 1.87 ± 1.01 μg m−3 during post-COVID-19 pandemic, respectively. The XGBoost-SHAP model indicated that emission sources had the most significant effect on OC and EC concentrations, followed by meteorological factors. Unfavorable meteorological conditions and a substantial increase in emissions are responsible for the increase of OC and EC concentration in winter. Potential source contribution function results indicated that the southern, eastern, and central Shandong regions were the primary source areas for transporting high concentrations of carbonaceous components. Positive matrix factorization analysis suggested that carbonaceous aerosols in Qingdao predominantly originated from coal/biomass combustion (54.75%–81.78%) and local vehicle emissions (8.72%–28.73%). Compared with that before COVID-19, coal/biomass combustion's contribution to OC and EC decreased by 19% after the COVID-19 pandemic. The contribution of vehicles increased by 110%, possibly due to the increase in motor vehicles and the rapid recovery in diesel consumption in freight transportation. Prohibiting biomass burning, such as open burning of straw, and measures such as promoting low-carbon and clean production of coal-fired industrial furnaces might have played a key role in reducing OC and EC levels. These results contribute to a deeper understanding of the concentration levels and sources of carbonaceous components in PM 1 and provide theoretical guidance for environmental management. [Display omitted] • Carbonaceous aerosols in PM 1 decreased based on the 6-year measurements. • Driving factors of OC and EC in PM 1 were identified by machine learning method. • PMF and PSCF analysis revealed a dramatic change in sources of OC and EC. • Increased vehicles and diesel consumption contributed more during the post-COVID-19. [ABSTRACT FROM AUTHOR]