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Potential health benefits from improved ambient air quality during the COVID-19 shutdown have been recently reported and discussed. Despite the shutdown measures being in place, northern China still suffered severe haze episodes (HE) that are not yet fully understood, particularly how the source emissions changed. Thus, the meteorological conditions and source emissions in processing five HEs occurred in Beijing-Tianjin-Hebei area were investigated by analyzing a comprehensive real-time measurement dataset including air quality data, particle physics, optical properties, chemistry, aerosol lidar remote sensing, and meteorology. Three HEs recorded before the shutdown began were related to accumulated primary pollutants and secondary aerosol formation under unfavorable dispersion conditions. The common "business as usual" emissions from local primary sources in this highly polluted area exceeded the wintertime atmospheric diffusive capacity to disperse them. Thus, an intensive haze formed under these adverse meteorological conditions such as in the first HE, with coal combustion to be the predominant source. Positive responses to the shutdown measures were demonstrated by reduced contributions from traffic and dust during the final two HEs that overlapped the Spring and Lantern Festivals, respectively. Local meteorological dispersion during the Spring Festival was the poorest among the five HEs. Increased residential burning plus fireworks emissions contributed to the elevated PM 2.5 with the potential of enhancing the HEs. Our results highlight that reductions from shutdown measures alone do not prevent the occurrence of HEs. To further reduce air pollution and thus improve public health, abatement strategies with an emphasis on residential burning are needed. [Display omitted] • Even with increased emissions controls, high pollution events occur in China. • "Business as usual" emissions in Tianjin exceeded winter diffusive capacity. • COVID shutdown reductions were offset by residential burning and fireworks. • Coal combustion remains a major source of PM 2.5. Fireworks plus residential burning contributed to the elevated PM 2.5 with the potential of enhancing hazes. [ABSTRACT FROM AUTHOR]

Vehicular non-exhaust emissions account for a significant share of atmospheric particulate matter (PM) pollution, but few studies have successfully quantified the contribution of non-exhaust emissions via real-world measurements. Here, we conduct a comprehensive study combining tunnel measurements, laboratory dynamometer and resuspension experiments, and chemical mass balance modeling to obtain source profiles, real-world emission factors (EFs), and inventories of vehicular non-exhaust PM emissions in Chinese megacities. The average vehicular PM 2.5 and PM 10 EFs measured in the four tunnels in four megacities (i.e., Beijing, Tianjin, Zhengzhou, and Qingdao) range from 8.8 to 16.0 mg km−1 veh−1 and from 37.4 to 63.9 mg km−1 veh−1, respectively. A two-step source apportionment is performed with the information of key tracers and localized profiles of each exhaust and non-exhaust source. Results show that the reconstructed PM 10 emissions embody 51–64% soil and cement dust, 26–40% tailpipe exhaust, 7–9% tire wear, and 1–3% brake wear, while PM 2.5 emissions are mainly composed of 59–80% tailpipe exhaust, 11–31% soil and cement dust, 4–10% tire wear, and 1–5% brake wear. Fleet composition, road gradient, and pavement roughness are essential factors in determining on-road non-exhaust emissions. Based on the EFs and the results of source apportionment, we estimate that the road dust, tire wear, and brake wear emit 8.1, 2.5, and 0.8 Gg year−1 PM 2.5 in China, respectively. Our study highlights the importance of non-exhaust emissions in China, which is essential to assess their impacts on air quality, human health, and climate and formulating effective controlling measures. Image 1 • Six traffic-related sources were resolved and quantified via tunnel measurements. • Non-exhaust dominate PM 10 emission and significantly contribute to PM 2.5 emission. • Deposited tire wear particles accounted for a considerable share of road dust. • Fleet composition, pavement gradient and roughness result in emission variability. [ABSTRACT FROM AUTHOR]

The multi-scale chemical characteristics and source apportionment of volatile organic compounds (VOCs) were analysed in Tianjin, China, using 1-hr resolution VOC-species data between November 1, 2018 and March 15, 2019. The average total VOC (TVOC) concentration was 30.6 ppbv during the heating season. The alkanes accounted for highest proportion of the TVOC, while the alkenes were the predominant species forming ozone, especially ethylene. Compared to the clean period, the concentration of acetylene during the haze events showed highest increase rate, followed by the ethane; and the concentrations and proportions of alkanes and alkenes were highest during the growth stage (GS) of haze events. The multi-scale apportionment results suggested petrochemical industry and solvent usage (PI/SU, 31.2%), vehicle emissions and liquefied petroleum gas (VE/LPG, 20.5%), and combustion emissions (CE, 19.1%) were the main VOC sources during the heating season. Compared to the clean period, the contributions of PI/SU, VE/LPG, CE, and refinery emissions notably increased during the haze events, while that of gasoline evaporation decreased. The contributions of PI/SU and RPI showed significantly increase during the GS of haze events, whereas most sources decreased during the dissipation stage of haze events. Diurnal-variations in source contributions during the haze events were clearer than the clean period, and the contributions of PI/SU, VE/LPG, and CE during the haze events were markedly higher at night. These findings provide valuable information to inform effective VOC control and prevention measures with specific relevance for the control of ozone pollution in Tianjin. Image 1 • Acetylene increased most significantly during the haze events than the clean period. • Ethylene was a predominant species forming ozone. • Gasoline evaporation significantly decreased during the haze events. • Petrochemical industry and solvent usage notably increased in the haze-event growth-stage. [ABSTRACT FROM AUTHOR]

Gasoline vehicles (GVs) emissions generally dominate ambient volatile organic compounds (VOCs) in urban areas, while VOC emissions from liquefied natural gas (LNG)-fueled vehicles play an increasingly important role in urban air quality, due to fuel transition from gasoline/diesel to alternative fuels. Here, an extensive dataset of VOC samples collected in three urban tunnels in China was used to explore real-world emission characteristics of ninety-nine VOC species from both GVs and LNG-fueled vehicles. The fleets in the Beijing and Tianjin tunnels comprised > 94% GVs whereas the fleet in the Nanjing tunnel comprised both GVs (∼ 87%) and LNG-buses (∼ 13%). The VOC emission factors (EFs) in the Beijing tunnel and Tianjin tunnel were highly correlated, implying that they can be applied as existing emission datasets from GVs with aim of distinguishing emissions from LNG-fueled vehicles and GVs in the Nanjing tunnel. For fleet emissions, the average VOC EFs have declined substantially over the last decade; the relative compositions of benzene, toluene, and ethylbenzene were quite stable despite differences in fleet composition. Ethylene, isopentane, ethane, and toluene; and ethane and propane were enriched in VOC emissions (v ∕ v) from GVs and LNG-fueled vehicles, respectively. Methyl t e r t -butyl ether, 2,2,4-trimethylpentane, 2,3,4-trimethylpentane, 3-methylpentane, and methylcyclopentane were potential VOC tracers for GVs. Ethane, propane, and 2,3-dimethylbutane were key tracers that distinguished LNG-fueled vehicles from GVs. Propane, isobutane, and n-butane were key VOC tracers that distinguished liquefied petroleum gas-fueled vehicles from GVs. Alkanes dominated fleet emissions both by mass and by volume. However, aromatics and alkenes (mainly ethylene and propylene) dominated VOC reactivity from gasoline- and LNG-fueled vehicles, respectively. Our study highlights that the wide discrepancy in fleet VOC emissions could be attributed to fleet compositions. • Inconsistent fleet-average VOC emissions due to different fleet compositions. • Real-world VOC emissions from gasoline vehicles (GVs) were measured in two tunnels with >94% GVs in the fleets. • Constrained linear regression was used to distinguish VOC emissions from LNG-fueled vehicles and GVs. • Fleet-average emission factors of VOCs substantially decreased over the last decade. • Aromatics and alkenes dominated VOC reactivity from gasoline- and LNG-fueled vehicles, respectively. [ABSTRACT FROM AUTHOR]