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South Asian air pollutants exert substantial effect on the climate and environment change over the Tibetan Plateau (TP). This paper investigates the trans-boundary transport of PM 10 , PM 2.5 , and O 3 from South Asia to the TP via WRF-Chem sensitive analysis. It is found that PM 10 , PM 2.5 , and O 3 over South Asia are mainly sourced from anthropogenic sources. South Asian emissions contribute up to 54% of PM 10 (PM 2.5) in the TP in the pre-monsoon season. For O 3 , the highest contribution of 18.13% is in the monsoon season, while the lowest contribution of 8.67% is in the winter season. To evaluate the respective contributions of anthropogenic and biomass burning emissions in South Asia to PM 10 , PM 2.5 , and O 3 in the TP, anthropogenic and biomass burning emissions in South Asia are considered separately. The results show that the largest percentage contribution of PM 10 (PM 2.5) from South Asian anthropogenic emissions to PM 10 (PM 2.5) in the TP with value of 35.86% (37.77%) occurs in winter, while the lowest percentage contribution of 16.52% (16.77%) appears in the monsoon season. For O 3 , the largest contribution of 17.74% from South Asian anthropogenic emissions appears in the monsoon season, whereas the lowest contribution of 8.59% occurs in winter. Compared to the anthropogenic emissions, the biomass burning emissions in South Asia have a relative less contribution to PM 10 , PM 2.5 , and O 3 in the TP. The largest contribution of PM 10 (PM 2.5) from South Asian biomass burning emissions to PM 10 (PM 2.5) in the TP is 20.04% (18.37%) in the pre-monsoon season. Conversely, the lowest contribution of 0.58% (0.53) appears in the monsoon season. O 3 from South Asian biomass burning emissions contributes <1% to O 3 in the TP in each season, implying that the biomass burning emissions in South Asia have little effect on O 3 in the TP. This study is of great significance to the ecological environment protection for the TP. • Contributions of South Asian emissions to PM 10 , PM 2.5 , and O 3 in the TP are quantified. • Anthropogenic emissions in South Asia have a larger contribution to PM 10 , PM 2.5 , and O 3 in the TP. • O 3 from South Asian biomass burning emissions contributes <1% to O 3 in the Tibetan Plateau. [ABSTRACT FROM AUTHOR]

Aerosol particles with diameters larger than 40 nm were collected during the flight campaign StratoClim 2017 within the Asian tropopause aerosol layer (ATAL) of the 2017 monsoon anticyclone above the Indian subcontinent. A multi-impactor system was installed on board the aircraft M-55 Geophysica, which was operated from Kathmandu, Nepal. The size and chemical composition of more than 5000 refractory particles/inclusions of 17 selected particle samples from seven different flights were analyzed by use of scanning electron microscopy (SEM) and transmission electron microscopy (TEM) combined with energy dispersive X-ray (EDX) microanalysis. Based on chemical composition and morphology, the refractory particles were assigned to the following particle groups: extraterrestrial, silicates, Fe-rich, Al-rich, Hg-rich, other metals, C-rich, soot, Cl-rich, and Ca-rich. Most abundant particle groups within the refractory particles are silicates and C-rich (non-volatile organics). In samples taken above the tropopause, extraterrestrial particles are becoming increasingly important with rising altitude. The most frequent particle sources for the small (maximum in size distribution DP-max=120 nm) refractory particles carried into the ATAL are combustion processes at the ground (burning of fossil fuels/biomass burning) and the agitation of soil material. The refractory particles in the ATAL represent only a very small fraction (< 2 % by number for particles > 40 nm) of the total aerosol particles, which are dominated by species like ammonium, sulfate, nitrate, and volatile organics. During one flight, a large number of very small (DP-max=25 nm) cinnabar particles (HgS) were detected, which are supposed to originate from a ground source such as coal combustion or underground coal fires. [ABSTRACT FROM AUTHOR]

Over the past few decades, the tropospheric ozone precursor anthropogenic emissions: nitrogen oxides (NOx) and reactive carbon (RC) from mid-latitude regions have been decreasing, and those from Asia and tropical regions have been increasing, leading to an equatorward emission redistribution. In this study, we quantify the contributions of various sources of NOx and RC emissions to tropospheric ozone using a source attribution technique during the 2000–2018 period in a global chemistry transport model: CAM4-Chem. We tag the ozone molecules with the source of their NOx or RC precursor emission in two separate simulations, one for each of NOx and RC. These tags include various natural (biogenic, biomass burning, lightning and methane), and regional anthropogenic (North American, European, East Asian, South Asian etc.) precursor emission sources. We simulate ~336 Tg O3 with an increasing trend of 0.91 Tg O3/yr (0.28 %/yr), largely contributed (and trend driven) by anthropogenic NOx emissions and methane. The ozone production efficiency of regional anthropogenic NOx emissions increases significantly when emissions decrease (Europe, North American and Russia-Belarus-Ukraine region's emissions) and decreases significantly when emissions increase (South Asian, Middle Eastern, International Shipping etc.). Tropical regions, despite smaller emissions, contribute more to tropospheric ozone burden compared to emissions from higher latitudes, consistent with previous work, due to large convection at the tropics thereby lifting O3 and its precursor NOx molecules into the free troposphere where ozone's lifetime is longer. We contrast the contribution to tropospheric ozone burden with that of the contribution to the global surface ozone. We simulate a smaller relative contribution from tropical regions to the global mean surface ozone compared to their contribution to the tropospheric ozone burden. The global population-weighted mean ozone (related to ozone exposure) is much larger compared to surface mean, mainly due to large anthropogenic emissions from densely populated regions: East Asia, South Asia, and other tropical regions, and a substantial contribution from international ship NOx emissions. The increasing trends in anthropogenic emissions from these regions are the main drivers of increasing global population-weighted mean ozone. [ABSTRACT FROM AUTHOR]