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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]

An extensive study was conducted to comprehensively assess simultaneous quantitative estimates of biomass burning organic carbon (OC-BB) within fine particulate matter (PM 2.5) across four distinct sites encompassing metropolitan and rural regions of Northeast Asia during the spring season. PM 2.5 samples were simultaneously collected in sites in Seoul and Seosan (SE: urban and SS: rural, Korea, respectively), Beijing (BJ: urban, China) and Ulaanbaatar (UB: urban, Mongolia), spanning from March to April 2022. The analysis of these samples aimed to quantify BB markers, including levoglucosan, mannosan, and K+, alongside OC. This analysis aimed to provide valuable insights into the impact and contribution of BB to PM 2.5 and OC. BB types were identified using levoglucosan/K+-BB and levoglucosan/mannosan ratios. In addition, our study focused on deriving an optimized OC/levoglucosan ratio, which is crucial for the accurate estimation of OC-BB concentrations. Moreover, an approach utilized in this study can be applied in other regions to estimate region-specific OC ∕ levoglucosan ratios for OC-BB. The contribution of OC-BB to total OC varied significantly across sites: SE (27 ± 17%), SS (60 ± 24%), BJ (5 ± 3%), and UB (51 ± 14%). Concentrations of levoglucosan and OC-BB were highest at UB and SS, indicating a greater impact of BB aerosols compared to SE and BJ. Cluster and potential source contribution function analyses showed that in SE, aerosols were influenced by BB originating from both the northwest and southwest directions. Conversely, in SS, the presence of aged, regional, and long-range transported aerosols from the northwest and south directions was observed. This study has the potential to assist in devising precise strategies aimed at mitigating BB, thus fostering improved air quality and environmental protection. • An optimized OC/levoglucosan ratio was developed for accurate estimation of OC-BB concentrations. • The impact of BB in Northeast Asia was quantitatively estimated using levoglucosan, mannosan, and K+ as tracers. • Hardwood, softwood, crops, and grass were the likely main sources of OC from BB in Northeast Asia. [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]

Atmospheric particulate matter (PM) pollution in Beijing and Seoul is an urgent concern because of the dense population and the role of the capital city. This study aimed to understand haze formation over East Asia during winter by simultaneously measuring the in situ aerosol chemical composition in the two megacities. During the sampling period, a similar pollution situation characterized by extremely low SO 2 (approximately 1 ppbv) and high NO x (approximately 20 ppbv) concentrations and secondary inorganic aerosol (SIA)-dominated PM was found in both cities. Nitrate dominated the inorganic components in the submicron particles in both cities and was more pronounced in Seoul than in Beijing. The enhanced SIA mass concentrations during pollution episodes were observed to be associated with an increased local atmospheric oxidation capacity (indicated by O 3 +NO 2 =O x concentration) and ambient relative humidity under similar stagnant weather conditions. Regarding the thermodynamic equilibrium, abundant aerosol liquid water promoted the partitioning of gaseous HNO 3 into its particle phase when pollution events occurred. This result emphasized the importance of local secondary aerosol formation for atmospheric PM pollution in East Asian megacities. The box model simulation of nitrate formation indicated that the homogeneous oxidation of NO 2 by OH radicals was the major nitrate formation pathway in both megacities. The downward transport of nitrate from the residual layer also significantly contributed to nitrate concentrations. NO x and volatile organic compounds (VOCs) exhibited a non-linear relationship with nitrate formation. Reducing VOCs concentrations was an efficient approach to mitigate nitrate in both megacities. A reduction of more than 50% in NO x concentrations was required for the effective reduction of nitrate. This study highlighted that Beijing and Seoul were experiencing similar PM pollution situations, and nitrate reduction should be considered to improve their air quality. • Secondary aerosol dominate the particulate matters pollution in East Asia. • High atmospheric oxidation capacity and humidity promote nitrate formation. • Both NO x and VOCs should be controlled to decline the particulate nitrate formation. [ABSTRACT FROM AUTHOR]