The range and time of the environmental effects of Asian dust are closely dependent on the pathways and the speed of dust plume movement. In this study, the occurrence and movement of two dust storms in China in May 2017 were examined by using open space- and ground-based measurement data and the backward trajectories of dust plumes. Results from the European Centre for Medium-Range Weather Forecasts (ECMWF) reanalysis data showed that the dust storms were caused by the rapid coupling development of Mongolian cyclones and Asian highs. After the dust plumes arrived at the Southeastern China in the first dust event, the stable weather conditions and the Asian high slowed down the movement of the plumes, leading to the gradual diffusion of dust particles. Moreover, the Asian high in the first event and the Huabei low (a low-pressure system in North China Plain) in the second altered the movement direction of the dust plumes from southward to northward, which we denote as the “dust reverse transport (DRT)”. The DRT occurred only within the lower troposphere even though dust plumes could extended to 5–10 km in vertical direction. Statistical results of 28 spring dust events occurred in 2015–2018 showed that all these dust storms were triggered by Mongolian cyclones and/or Asian highs, and approximately 39% moved as the DRT, indicating about one third of severe spring dust storms could influence larger areas or longer time than the remained ones.

Fine particulate matter (PM_2.5) was simultaneously collected from the indoor and outdoor environments in urban area of Jinan in North China from November to December 2018 to evaluate the characteristics and sources of indoor PM_2.5 pollution. The concentrations of indoor and outdoor PM_2.5 were 69.0 ± 50.5 µg m⁻³ and 128.7 ± 67.9 µg m⁻³, respectively, much higher than the WHO-established 24-h standards for PM_2.5, indicating serious PM_2.5 pollution of indoor and outdoor environments in urban Jinan. SO₄²⁻, NO₃⁻, NH₄⁺, and organic carbon (OC) were the predominant components, which accounted for more than 60% of the PM_2.5 concentration. The total elemental risk values in urban Jinan for the three highly vulnerable groups of population (children (aged 2–6 years and 6–12 years) and older adults (≥70 years)) were nearly 1, indicating that exposure to all of the elements in PM_2.5 had potential non-carcinogenic risks to human health. Further analyses of the indoor/outdoor concentration ratios, infiltration rates (F_INF), and indoor-generated concentration (C_ig) indicated that indoor PM_2.5 and its major chemical components (SO₄²⁻, NO₃⁻, NH₄⁺, OC, and elemental carbon) were primarily determined by outdoor pollution. The lower indoor NO₃⁻/SO₄²⁻ ratio and F_INF of NO₃⁻ relative to the outdoor values were due to the volatility of NO₃⁻. Positive matrix factorization (PMF) was performed to estimate the sources of PM_2.5 using the combined datasets of indoor and outdoor environments and revealed that secondary aerosols, dust, cement production, and coal combustion/metal smelting were the major sources during the sampling period.

Photodegradation is a key process impacting the lifetime of oxalate in the atmosphere, but few studies investigated this process in the field due to the complex mixing and sources of oxalate. Oxalate-containing particles were measured via single-particle aerosol mass spectrometry at coastal and suburban sites in Qingdao, a coastal city in North China in the summer of 2016. The mixing state and influence of different ambient conditions on the source and photodegradation of oxalate were investigated. Generally, 6.3% and 12.3% of the total particles (by number) contained oxalate at coastal and suburban sites, respectively. Twelve major types of oxalate-containing particles were identified, and they were classified into three groups. Biomass burning (BB)-related oxalate–K and oxalate–carbonaceous particles were the dominant groups, respectively, accounting for 68.9% and 13.6% at the coastal site and 72.0% and 16.8% at the suburban site. Oxalate–Heavy metals (HM)-related particles represented 14.6% and 9.3% of the oxalate particles at coastal and suburban sites, respectively, which were mainly from industrial emissions (Cu-rich, Fe-rich, Pb-rich), BB (Zn-rich), and residual fuel oil combustion (V-rich). The peak area of oxalate at the coastal site decreased immediately after sunrise, while it increased during the daytime at the suburban site. However, the oxalate peak area of Fe-rich particles at both sites decreased after sunrise, indicating that iron plays an important role in oxalate degradation in both environments. The decay rates (k) of Fe-rich and BB-Fe particles at the coastal site (−0.978 and −0.859 h⁻¹, respectively), were greater than those at the suburban site (−0.512 and −0.178 h⁻¹, respectively), owing to the high-water content of particles and fewer oxalate precursors. The estimated k values of oxalate peak area for different ambient conditions were in the same order of magnitude, which can help establish or validate the future atmospheric models.