Impact of Encouraging Vehicles to Refuel at Night on Ozone and Non-Methane Hydrocarbons (NMHCs): A Case Study in Ji’nan, China

Abstract

Gasoline evaporation is a potential source of ambient non-methane hydrocarbons (NMHCs) during summer, and thus the policy of encouraging vehicles to refuel at night has been implemented to control ground-level ozone (O3) and NMHCs. In this study, NMHCs and trace gases were observed online at an urban site of Ji’nan during May–July in 2019 and 2020 to assess the impact of this policy. After the implementation of this policy, the average concentration of daily maximum 8 h moving average O3 decreased from 198 μg/m3 to 181 μg/m3. Meanwhile, the average mixing ratio of NMHCs decreased from 19.89 ppbv to 18.02 ppbv. Sources of NMHCs were then apportioned using the positive matrix factorization model. Four factors were resolved and identified, including vehicle exhaust, paint and solvents usage, gasoline evaporation, and biogenic emission. Relative contributions of these four sources were 52.5%, 20.6%, 18.3%, and 8.6%, respectively. After the implementation of this policy, relative contributions of gasoline evaporation in 1:00–4:00 increased from 20.2–22.7% to 25.4–28.2%, while those for 16:00–18:00 decreased from 16.8–18.7% to 13.9–15.7%. The non-linear relationship of O3 with NMHCs and NOx was investigated using a box model based on observations. Results suggest that O3 production was mainly controlled by NMHCs. Aromatics and alkenes were the key NMHC species in O3 formation. Furthermore, two scenarios of encouraging vehicles to refuel at night were designed to evaluate their impact on O3. The relative decreases of O3 peak concentrations were lower than 1%, indicating that this policy had a limited impact on O3 during the observation period.

Keywords

• gasoline evaporation
• O₃ sensitivity
• NMHCs
• source apportionment