Abstract
Ground-level ozone (O3) pollution is still one of the priorities and challenges for air pollution control in the Yangtze River Delta (YRD) region of China. Understanding the relationship of O3 with its precursors and contributions of different sources in O3 formation is essential for the development of an O3 control strategy. This study analyzed O3 sensitivity to its precursors using a box model based on online observations of O3, non-methane hydrocarbons (NMHCs), nitrogen oxides (NOx), and carbon monoxide (CO) at an urban site and a suburban site in Shanghai in July 2017. Anthropogenic sources of NMHCs were identified using the positive matrix factorization (PMF) receptor model, and then contributions of different sources in O3 formation were estimated by the observation-based model (OBM). The relative incremental reactivity (RIR) values calculated by the OBM suggest that O3 formation at the urban site was in the NMHC-limited regime, while O3 formation at the suburban site tended between the transition regime and the NMHC-limited regime. Vehicular emission and liquefied petrochemical gas (LPG) use or aged air mass were found to be the two largest contributors at the urban and suburban sites in July, followed by paint and solvent use, and the petrochemical industry. However, from the perspective of O3 formation, vehicular emission and paint and solvent use were the largest two contributors at two sites due to the higher RIR values for paint and solvent use. In addition, the influence of transport on O3 sensitivity was identified by comparing O3 sensitivity at the suburban site across two days with different air mass paths. The result revealed that O3 formation in Shanghai is not only related to local emissions but also influenced by emissions from neighboring provinces. These findings on O3–NMHC–NOX sensitivity, contributions of different sources in O3 formation, and influence of transport could be useful for O3 pollution control in the YRD region. Nevertheless, more quantitative analyses on transport and further evaluation of the uncertainty of the OBM are still needed in future.
Highlights
Ground-level ozone (O3 ) pollution in China is becoming of increasing concern in recent years.The China Environment Report [1] showed that the 90th percentile for the daily maximum 8-h moving average (DMA-8h) O3 concentration for 74 major cities in China increased from 139 μg/m3 to 169 μg/m3 during 2013–2017
Two studies used volatile organic compounds (VOCs)/nitrogen oxides (NOx) measured at urban sites in Shanghai to analyze O3 sensitivity, and they suggested that O3 formation was mainly controlled by VOCs [13,14]
The relative incremental reactivity (RIR) values for anthropogenic hydrocarbons (AHCs) (RIR(AHC)) and NHC (RIR(NHC)) were both positive at these two sites, suggesting that reducing AHC and/or NHC would result in O3 decrease during O3 pollution episodes
Summary
Ground-level ozone (O3 ) pollution in China is becoming of increasing concern in recent years. Two studies used VOCs/NOx measured at urban sites in Shanghai to analyze O3 sensitivity, and they suggested that O3 formation was mainly controlled by VOCs (i.e., a VOC-limited regime) [13,14]. The OBM study by Tan et al [15] suggested that O3 formation at an urban site in Shanghai was in a VOC-limited regime. VOC source apportionment with O3 sensitivity results were conducted in Shanghai to estimate the contribution of different VOC sources to O3 formation. O3 sensitivity to its precursors was analyzed using an OBM based on online measurements of O3 , non-methane hydrocarbons (NMHCs), NOx , and CO at an urban and a suburban site in Shanghai in July 2017. Trajectory analysis was conducted to evaluate the influence of transport in a case study
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