Ground-level ozone (O₃), which is mainly from the photochemical reactions of NO_x and volatile organic compounds (VOCs), has become a crucial pollutant obstructing air quality improvement in China. Understanding the composition, temporal variability and source apportionment of VOCs is necessary for determining effective control measures to minimize VOCs and their related photochemical pollution. To provide a comprehensive analysis of VOC sources and their contributions to ozone formation in the city of Chengdu—a megacity with the highest rates of industrial and economic development in southwest China—we conducted a one-month monitoring project at three urban sites (Shuangliu, Xindu, Junpingjie; SL, XD and JPJ, respectively) along the main north–south meteorological transport channel before and during the implemented control measures. Alkanes were the dominant group at each site, contributing to around 50% of the observed total VOCs, followed by oxygen-containing VOCs (OVOCs), aromatics, halohydrocarbons and alkenes. During the control period, the mixing ratios of most measured VOC species decreased, and O₃ concentrations were down by at least 20%. VOC species experiencing the most effect from control were aromatics and OVOCs, which had higher O₃ formation reactivity. This indicated that the control policies had significant influence on reductions of reactive VOC species. We also identified VOC sources at SL and XD using positive matrix factorization (PMF) and assessed their contributions to photochemical O₃ formation by calculating the O₃ formation potential (OFP) based on mass concentrations and maximum incremental reactivity of related VOCs. Five dominant VOC sources were identified, with the highest contributions from vehicular exhaust and fuel evaporation before control, followed by solvent utilization, biogenic background and secondary formation, and industrial emissions. Contribution from vehicular exhaust was reduced the most at SL, while at XD, secondary formation VOCs decreased significantly. VOCs from vehicular and industrial emissions and solvent utilization were found to be the dominant precursors for OFPs, particularly the species of xylenes, toluene and propene. Our results therefore suggest that priority should be given to the alleviation of photochemical pollutants for effective control of O₃ formation in Chengdu. The findings from this work have important implications for formulating effective emission control policies in Chengdu.

Surface ozone (O₃) pollution has not improved significantly in recent years. It is still the primary air pollution problem in many megacities in China during summertime. In high temperature and intense radiation weather, volatile organic compounds (VOCs) are easily oxidized and degraded to induce O₃ pollution. In order to understand the impact of difference between photochemical initial concentration (PIC) of VOCs and the actual measured concentration on O₃ formation, a campaign was carried out during O₃ pollution in Chengdu (25 July–5 August 2021). During this O₃ pollution episode, the maximum value of O₃ concentration reached 335.0 μg/m³, and the precursor concentrations increased significantly. The mean values of VOC_measured and VOC_PICs were 19.7 ppbv and 30.7 ppbv, corresponding to O₃ formation potential (OFP) of 175.3 μg/m³ and 478.8 μg/m³, respectively, indicating that the consumption of VOCs content could not be ignored. Alkenes accounted for 77.2% of VOCs consumption. Alkenes and aromatics contributed 63.0% and 29.2% to OFP values which derived from PIC of each VOC species. The relative incremental reactivity analysis based on PICs showed that the O₃ formation was controlled by the cooperation of nitrogen oxides (NOx) and VOCs, and the effect of NOx emission reduction was better.

Complex air pollution, including particulate matter and ozone, is a significant environmental issue in China, with volatile organic compounds (VOCs) as key precursors. Traditional ground-based monitoring methods struggle to capture the vertical distribution and changes of pollutants in the troposphere. To address this, we developed a vertical monitoring and sampling platform using a quadcopter unmanned aerial vehicle (UAV). The platform, equipped with lightweight quartz sampling canisters and miniaturized sensors, collects air samples for VOC analysis and vertical data on meteorological parameters and particulate matter. Performance tests showed the quartz canisters had less than 15% adsorption loss, with sample storage stability exceeding 80% over three days. Sensor data showed strong correlations with standard instruments (R² > 0.80). Computational fluid dynamics simulations optimized the sampler’s inlet position and ascertained that ascending flight mitigates rotor-induced air recirculation. Field campaigns were conducted at six sites along the Chengdu Metropolitan Circle Ring Expressway. Vertical data from 0~300 m revealed particulate matter concentrations peaked at 50~70 m. Near-surface VOCs were dominated by alkanes, while aromatics were found concentrated at 150~250 m, indicating significant regional transport influences. The results confirmed the platform’s effectiveness for pollutant distribution analysis.

This basic study conducted an X-ray fluorescence (XRF) analysis on pseudo-binary samples, which emphasis on the binary influence coefficient and correction for matrix effects. The Ti-V, V-Ti, Ti-Fe, Fe-Ti, V-Fe and Fe-V samples were confected and measured by XRF analysis using a Si-PIN detector. These coefficients were calculated using mathematical models proposed through the Lachance-Traill algorithm, which can be applied in practice via an efficient calibration procedure. For the content measurement, the maximum absolute error decreased from 5.92% to 0.27%, and the relative error decreased from 14.84% to 0.66% via fitting correction for matrix effects. This study describes and emphasizes the application of the binary influence coefficient and fitting correction method.

This study improved the computation theory “Ozone Weekend Effect Method” (OWEM) and analyzed the 2016 observation data from the state-controlled ambient air quality monitoring sites in Chengdu using the OWEM theory. The improved OWEM theory is then applied to processing large sample data and making a judgment on photochemical reaction sensitivity in Chengdu. The result of applying the OWEM theory to Chengdu shows 1) that the VOCs-limited period, the NOx-limited period and the photochemical reaction steady-state period, R_t, accounted for 66.06%, 33.64% and 0.30%, respectively; 2) that on a seasonal basis, i.e. in the ozone photochemical reaction occurring in spring, summer, autumn and winter 2016 in Chengdu, the VOCs-limited period accounted for 59.40%, 72.49%, 63.85% and 68.49% of the 2016 observed data, respectively, and the NOx-limited period accounted for 39.70%, 27.51%, 36.15% and 31.19%respectively; 3) that in the VOCs-limited period and the NOx-limited period of August 2016, the month when the most serious ozone pollution of that year occurred in Chengdu, R_t accounted for 70.0% and 30.0%, respectively, and that there was no photochemical reaction steady-state zone period that month; 4) and that through estimation, it is suggested that as for the ozone pollution control of Chengdu, the ratio of VOCs emission reduction to NOx emission reduction should be around 3:1.