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Due to increasingly stringent control policy, air quality has generally improved in major cities in China during the past decade. However, the standards of national regulation and the World Health Organization are yet to be fulfilled in certain areas (in some urban districts among the cities) and/or certain periods (during pollution episode event). A further control policy, hence, has been issued in the 13th Five-Year Plan (2016–2020, hereafter 13th FYP). It will be of interest to evaluate the air quality before the 13th FYP (2015) and to estimate the potential air quality by the end of the 13th FYP (2020) with a focus on the area of an urban district and the periods of severe pollution episodes. Based on observation data of major air pollutants, including SO2 (sulphur dioxide), NO2 (nitrogen dioxide), CO (carbon monoxide), PM10 (particulate matter with aerodynamic diameter equal to or less than 10 μm), PM2.5 (particulate matter with aerodynamic diameter equal to or less than 2.5 µm) and O3 (Ozone), the air quality of Haizhu district [an urban district in the Pearl River Delta (PRD), China] in 2015 suggested that typical heavy pollution occurred in winter and the hot season, with NO2 or PM2.5 as the key pollutants in winter and O3 as the key pollutant in the hot season. We also adopted a state-of-the-art chemical transport model, the Weather Research and Forecasting model coupled with Chemistry (WRF-Chem), to predict the air quality in Haizhu District 2020 under different scenarios. The simulation results suggested that among the emission control scenarios, comprehensive measures taken in the whole of Guangzhou city would improve air quality more significantly than measures taken just in Haizhu, under all conditions. In the urban district, vehicle emission control would account more than half of the influence of all source emission control on air quality. Based on our simulation, by the end of the 13th FYP, it is noticeable that O3 pollution would increase, which indicates that the control ratio of volatile organic compounds (VOCs) and nitrogen oxides (NOx) may be unsuitable and therefore should be adjusted. Our study highlights the significance of evaluating the efficacy of current policy in reducing the air pollutants and recommends possible directions for further air pollution control for urban areas during the 13th FYP. [ABSTRACT FROM AUTHOR]

• PM concentrations and inhalation doses in Guangzhou presented the following trend: shared bikes > buses > cars > subways. • The counts of particle size range of 0.25–0.5 µm were highest in all travel modes. • Travel by "cars CW" (i.e., with closed windows) effectively prevented PM infiltration from outside air. • PM concentrations on weekends with peaks usually observed in the morning, were higher than those on weekdays. Travelers are severely exposed to traffic-related particulate matter (PM). To assess the personal exposure to PM for multiple transportation modes, we conducted a study on particle concentrations, size fractions, and inhalation doses in Guangzhou, China. PM concentrations and inhalation doses showed the following trend: shared bikes > buses > cars > subways. PM 0.25-1 concentrations in subway accounted for 56%–63% of all size fractions, while PM 2.5-10 dominated PM 0.25-2.5 in other modes. The highest particle counts were observed in the size range of 0.25–0.5 µm. PM concentrations on weekends were higher than those on weekdays. Peak concentrations were usually recorded in the morning on weekends but in the evening during weekdays. Females had higher exposure risks than males for the same distance covered using shared bikes due to longer travel duration. These results can provide theoretical guides for travelers to reduce personal exposure and health risks associated with PM. [ABSTRACT FROM AUTHOR]

Daytime atmospheric pollution has received wide attention, while the vertical structures of atmospheric pollutants at night play a crucial role in the photochemical process on the following day, which is still less reported. Focusing on Guangzhou, a megacity of South China, we established an unmanned aerial vehicle (UAV) equipped with micro detectors to collect consecutive high-resolution samples of fine particle (PM 2.5), submicron particle (PM 1.0), black carbon (BC) and ozone (O 3) concentrations in the atmosphere, as well as the air temperature (AT) and relative humidity (RH) within a 500 m altitude during nighttime from Oct. 24th to Nov. 6th, 2018. The measurements showed that PM 2.5 , PM 1.0 , and BC decreased with altitude and were influenced by the nighttime shallow planetary boundary layer (PBL) where BC was more accumulated and fluctuated. In contrast, O 3 was positively correlated with altitude. Backward trajectory clustering and Pasquill stability classification showed that advection and convection significantly influenced the vertical distribution of all pollutants, particularly particulate matter. External air masses carrying high concentrations of pollutants increased PM 1.0 and PM 2.5 levels by 145% and 455%, respectively, compared to unaffected periods. The ratio of BC to PM 2.5 indicated that local emissions had a minor role in nighttime particulate matter. Vertical transport caused by atmospheric instability reduced the differences in pollutant concentrations at various heights. Geodetector and generalized additive model showed that RH and BC accumulation in the PBL were significant factors influencing vertical changes of the secondary aerosol intensity as indicated by the ratio of PM 1.0 to PM 2.5. The joint explanation of RH and atmospheric stability with other variables such as BC is essential to understand the generation of secondary aerosols. These findings provide insights into regional and local measures to prevent and control night-time particulate matter pollution. [Display omitted] • PM 2.5 , PM 1.0 , BC, and O 3 are detected vertically at nighttime in Guangzhou. • The vertical decline is smooth for PM 2.5 and PM 1.0 but fluctuating for BC. • Compared to PM 2.5 and PM 1.0 , BC is more sensitive to PBL. • Higher BC and humidity near the PBL reduce the secondary aerosol intensity. [ABSTRACT FROM AUTHOR]

Air pollution caused by PM 2.5 is a significant public health concern, with vehicle emissions being a major contributor. Previous research focused on assessing personal exposure in local traffic microenvironments, but this approach is resource-intensive and challenging to implement city-wide. Traditional methods of assessing population exposure have limitations in reflecting population mobility and spatiotemporal heterogeneity. This study presents a method for obtaining high-resolution spatiotemporal distributions of the population and their exposure to traffic-related PM 2.5 in Guangzhou using multisource data. The results indicate that the simulated population distribution was consistent with census data and allow identification of population density hotspots. Meanwhile, this study also examines 24-hour population changes for dynamic high-resolution assessment of population exposure. The findings show that low-income individuals and rural-urban migrants residing in urban villages have a mean population exposure exceeding 5.18 μg/min, surpassing the PM 2.5 exposure of commuters in enclosed cabins. This emphasizes the urgent need to mitigate the negative impacts of traffic-related PM 2.5 on public health. [ABSTRACT FROM AUTHOR]