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Ulaanbaatar (UB), the fast-growing capital of Mongolia, is known for its world's worst level of particulate matter (PM) concentrations in winter. However, current anthropogenic emission inventories over the UB are based on data from more than fifteen years ago, and satellite observations are scarce because UB is in high latitudes. During the winter of 2020–21, the first period of the Fine Particle Research Initiative in East Asia considering the National Differences (FRIEND), several times higher concentrations of PM in UB compared to other urban sites in East Asia were observed but not reproduced with a chemical transport model mainly due to the underestimated anthropogenic emissions. Therefore, we devised a method for sequentially adjusting emissions based on the reactivity of PM precursors using ground observations. We scaled emission rates for the inert species (CO, elemental carbon (EC), and organic carbon (OC)) to reproduce their observed ambient concentrations, followed by SO 2 to reproduce the concentration of SO 4 2−, which was examined to have the least uncertainty based on the abundance of observed NH 3 , and finally NO and NH 3 for NO 3 −, and NH 4 +. This improved estimation is compared to regional inventories for Asia and suggests more than an order of magnitude increase in anthropogenic emissions in UB. Using the improved emission inventory, we were able to successfully reproduce independent observation data on PM 2.5 concentrations in UB in December 2021 from the U.S. Embassy. During the campaign period, we found more than 50% of the SO 4 2−, NO 3 −, and NH 4 + increased in UB due to the improvement could travel to Beijing, China (BJ), and about 20% of the SO 4 2− could travel to Noto, Japan (NT), more than 3000 km away. Also, the anthropogenic emissions in UB can effectively increase OC, NO 3 −, and NH 4 + concentrations in BJ when Gobi dust storms occur. [Display omitted] • We assessed anthropogenic emission rates in Ulaanbaatar using ground observations. • Several folds of increments are needed for major anthropogenic species' emissions. • Independent observation at Ulaanbaatar is reproduced using the improved emissions. • Ulaanbaatar's emissions impacted aerosol levels in Beijing during the campaign. [ABSTRACT FROM AUTHOR]

In this study, the morphological and elemental properties of airborne fine particles (PM 2.5) collected during winter (15 December 2020–14 January 2021) in Ulaanbaatar, Mongolia, were investigated using scanning electron microscopy (SEM) combined with energy-dispersive X-ray spectrometry (EDS). SEM analysis of the PM 2.5 samples revealed that the particle shape distribution on haze days (daily mean PM 2.5 concentration of over 100 μg m−3) was irregular (62%), spherical (24.6%), cluster (10.7%), and chain-like (2.7%), while the particle shape on clean days (daily mean PM 2.5 concentration of less than 30 μg m−3) was distributed as follows: irregular (56%), cluster (22%), spherical (17.3%), and chain-like (4.7%). The apparent mean particle size on haze days (2.07 μm) was twofold greater than that on clean days (1.13 μm). Based on the EDS spectra, carbonaceous particles were the most abundant (38%), followed by mineral dust (36%), Fe-rich particles (4.7%), N-rich particles (4.7%), calcium sulfate (4%), fly ash (4%) and others (2%) on clean days. On haze days, carbonaceous particles accounted for 86% of the total, and Fe-rich, mineral, transition metal, and calcium sulfate particles accounted for 6.7, 4.7, 1.3 and 0.7%, respectively, indicating that carbonaceous particles were the main contributor on haze days. In particular, the sample filters collected on haze days were predominantly covered with tar/soot-like sticky matter, in contrast to those collected on clean days. Spearman's rank correlation analysis of PM 2.5 with inorganic gaseous components as well as meteorological conditions further revealed that high levels of PM 2.5 in winter in Ulaanbaatar were significantly associated with SO 2 (ρ = 0.95), and CO (ρ = 0.94). These associations indicated that ambient SO 2 and CO gases are indicative of haze episodes during the study period, and suggested a strong contribution of solid fuel combustion producing those gases in Ulaanbaatar during winter. [Display omitted] • Morphological and elemental properties of PM 2.5 in Ulaanbaatar was investigated. • Tar/soot-like sticky matter was abundantly observed on the sample filters of haze days. • Apparent mean particle size on haze days was twofold greater than that on clean days. • Ambient SO 2 and CO gases are indicative of haze episodes in Ulaanbaatar during winter. [ABSTRACT FROM AUTHOR]