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Driving conditions are among the important factors determining gasoline vehicle emissions, yet their relation with exhaust-derived secondary pollutants is poorly understood. Here, we introduced exhaust from a gasoline vehicle under hot idling and cruising conditions into an indoor smog chamber by using a chassis dynamometer and investigated the formation of secondary organic aerosols (SOA) during photochemical ageing under light after characterizing the primary emission of non-methane hydrocarbons (NMHCs), nitrogen oxide (NO x) and primary organic aerosol (POA) in the dark. When compared to emission factors (EFs) at idling, during cruising at 20 km h−1 or 40 km h−1, the EFs of NMHCs decreased by more than an order of magnitude, while the EFs of NO x were more than doubled, resulting in a large drop in the NMHC-to-NO x ratios. The percentages of reactive alkenes and aromatic hydrocarbons also decreased from idling to cruising at 20 km h−1 to that at 40 km h−1. The emission factor of benzene, a carcinogenic compound, decreased more than 10 times from ~0.35 g kg-fuel−1 at idling to ~0.03 g kg-fuel−1 during cruising. During photochemical ageing of exhaust, substantial SOA was formed, and the SOA/POA ratios decreased from 52 to 92 at idling to 4–14 during cruising. Traditional aromatics could explain 30–64% of the measured SOA at idling but less than 15% of the measured SOA during cruising. Our results highlight that traffic congestion would greatly promote the emission of reactive volatile organic compounds and carcinogenic benzene from gasoline vehicles and also show that NMHCs as a target in gasoline vehicle emission tests cannot effectively represent the SOA and ozone formation potentials of the partially oxidized hydrocarbons from poorly functioning converters. Unlabelled Image • Primary emissions and SOA formation from hot idling and cruising gasoline vehicle were compared. • Emissions at idling and cruising varied greatly in the NMHC/NOx ratios and NMHC compositions. • Aromatics could explain 30–64% of measured SOA at idling, but less than 15% of that at cruising. [ABSTRACT FROM AUTHOR]

The characteristics of long time series of CO 2 and CO surface concentrations, tropospheric and total column dry-air mole fractions (DMF) from May 2015 to December 2019 were investigated. Both CO 2 and CO show different seasonality for the three datasets. The annual increasing trend of CO 2 is similar for all three datasets. However, the annual decreasing trend of CO for surface concentration is high compared to the other two measurements, mainly due to the improved combustion efficiency from power generation in recent years. The correlation between the tropospheric and total atmospheric CO 2 and CO is higher than that between the surface concentration and tropospheric CO 2 and CO. This is because the tropospheric and total atmospheric results both have common vertical profiles for CO 2 and CO respective mole fractions that were observed in troposphere. Furthermore, the enhancement ratios of CO 2 to CO derived from the three datasets during the period from 2016 to 2019 were compared. The ratio of ∆CO 2 to ∆CO has an obvious increase with altitude each year, which means that the combustion efficiencies obtained from the three datasets are different. All ratios for the three datasets showed a slight increasing trend in recent years, which is attributed to increased combustion efficiency due to governmental measures for energy savings and emission reductions., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2022 The Authors. Published by Elsevier B.V. All rights reserved.)

The vertical distributions of formaldehyde (HCHO) and nitrogen dioxide (NO 2 ) and their indicative roles in ozone (O 3 ) sensitivity are important for designing O 3 mitigation strategies. Using hyperspectral remote sensing observations, tropospheric vertical profiles of HCHO, NO 2 , and aerosol extinction were investigated in Guangzhou, China from July to September 2019. On both O 3 non-exceedance and polluted days, the HCHO and aerosol vertical profiles exhibited similar Gaussian shapes, but the NO 2 profile exhibited an exponential decreasing shape. HCHO and aerosol were especially sensitive to O 3 pollution, with higher values generally occurring at approximately noon and late afternoon at higher altitudes. We attempted to study the diurnal evolution of O 3 sensitivity at different altitudes based on the HCHO to NO 2 ratio (FNR) vertical profile. The FNR thresholds marking the transition regime (2.5 < FNR < 4.0) were derived from the relationship between the increase in O 3 (∆O 3 ) and FNR. Our results showed that O 3 sensitivity tends to be VOC-limited both at lower (below approximately 0.4 km) and higher (above approximately 1.8 km) altitudes throughout the daytime. In the middle altitudes, the photochemical formation of O 3 was mainly in the transition/NO x -limited regime in the morning and afternoon but in the VOC-limited regime at noontime. The relationship between TROPOMI column FNR and near-surface O 3 sensitivity was further investigated. Compared with the MAX-DOAS near-surface FNR, slightly higher values of column FNR would increase the number of days classified as transition regimes, which was mainly caused by the inhomogeneous vertical distribution of HCHO and NO 2 in the lower troposphere. This study provides an improved understanding of vertical variability and diurnal evolution of O 3 formation sensitivity., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2022 Elsevier B.V. All rights reserved.)