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Air quality is often assessed using particulate matter (PM) mass concentration without considering its toxicity, thus possibly leading to improper control policies or inadequate health protection. Here, we studied differences in oxidative potentials (OPs) of PM samples collected using automobile air conditioning (AC) filters from 19 global cities, as well as influences from microbial contents. Dithiothreitol (DTT) assay showed remarkable differences in the PM OPs among cities (p -values ≤ 0.001, Kruskal-Wallis test). For example, the normalized index of oxidant generation (NIOG) of PM samples in San Francisco (2.20 × 10−2, annual average PM 10 = 16 μg/m3) was found to be twice that in Beijing (1.14 × 10−2, annual average PM 10 = 135 μg/m3). Limulus amebocyte lysate (LAL) assay found that PM-borne endotoxin ranged from 12.16 EU/mg (Florianopolis, Brazil) to 2518.23 EU/mg (Chennai, India) among cities. Besides, culturing method and real-time qPCR revealed significant differences of up to ∼100-fold in both bacterial and fungal levels among 19 cities. Spearman's correlation analysis implied that PM-borne microbes such as bacteria and fungi as well as metals could strongly influence the PM OP. As an example, our results in Xi'an, China further suggest that the PM 2.5 OP evolves for a particular city over the time, which is attributable to both the urbanization and air pollution control measures. This work highlights the importance in optimizing the current air quality control measures by considering the toxicity factor and its microbial constituents. Image 1 • Ambient PM toxicity per unit of mass was shown to vary greatly with different cities across the world. • PM-borne biologicals were shown to exhibit remarkable differences across major cities, contributing to the difference of PM toxicity. • PM toxicity was shown to evolve over the time as a result of ground human activities as well as air pollution control measures. • This work highlights the need of taking into account of PM toxicity for future air pollution control efforts. [ABSTRACT FROM AUTHOR]

As the capital of China, Beijing is the subject of great concern regarding atmospheric pollution, especially that of fine particulate matter (PM 2.5). In winter 2017 (i.e., November 2017 to February 2018), PM 2.5 concentration in Beijing decreased to its lowest value in the past ten years. In this study, we sought to investigate the impacts of meteorology and emission control on this abnormally low pollution phenomenon. Weather Research and Forecasting coupled with Chemistry (WRF-Chem) simulations show that sensitivity to meteorological factors accounts for approximately 51% of the observed change between winters 2016 and 2017 in Beijing. We further compared the pollution dispersion condition of winters 2016 and 2017 in terms of large-scale circulation patterns and local mixing layer heights (MLHs). The meteorological condition in 2017 was characterized by stronger wind speed (WS) and higher MLH. We classified circulation patterns into two types using the obliquely rotated Principal Component Analysis in T-mode (T-PCA) method. Active weather was found to be associated with high MLH, high near-surface WS, and high ventilation coefficient (VC), which favors the dispersion of pollutants. In contrast, the changes of meteorological variables and pollution conditions are almost opposite for stable weather. Active weather amounted to 73 and 85 days for winters 2016 and 2017, respectively. Stable weather conditions prevailed on 46 days in winter 2016, and 32 days in 2017. Less stable weather during winter 2017 compared with that of winter 2016 possibly favored efficient ventilation of boundary-layer pollution. A lack of persistent stable weather also contributed to low PM 2.5 concentration in 2017. This research is important for air-pollution assessment and regional environmental management. • The impacts on a low pollution phenomenon in Beijing, winter 2017 were investigated. • Fixed-emission simulations indicated a 32% sensitivity to meteorological factors. • Winter 2017 had higher wind speeds and mixing layer heights than winter 2016. • Lack of persistent stable weather contributed to low PM 2.5 concentration. [ABSTRACT FROM AUTHOR]

To better understand the chemical speciation of volatile organic compounds (VOCs) and their role in ground-level ozone formation in the Beijing-Tianjin-Hebei region, China, measurements of 56 non-methane hydrocarbons (NMHCs) and 12 carbonyls were conducted at three sites in summer. Alkanes were the largest group of NMHCs (>50%), followed by alkenes and aromatics. Acetone was the most abundant carbonyl species (>50%). The OH loss rates (L OH ) of VOCs were calculated to estimate their chemical reactivities. Alkenes played a predominant role in VOC reactivity, among which ethene and propene were the largest contributors. Isoprene contributed 11.61–38.00% of the total reactivity of measured VOCs. Alkenes and aromatics were the largest contributors (47.65–61.53% totally) to the total Ozone Formation Potential (OFP) of measured VOCs based on the observed mixing ratio. Isoprene was the most reactive species, but originated mainly from biogenic emissions. Ethene, m/p-xylene, toluene, propene, o-xylene, and 1-butene were considered to play significant roles in ground-level ozone formation in this region. The OFPs of total measured NMHCs increased by 10.20–22.05% when they were calculated based on the initial mixing ratio. Photochemical losses of hydrocarbons and the secondary formation of carbonyls in this region were also determined. Vehicle exhaust emissions contributed substantially to ambient VOCs. [ABSTRACT FROM AUTHOR]