Weekend-weekday variations, sources, and secondary transformation potential of volatile organic compounds in urban Zhengzhou, China

Periodical changes of human activities cause weekend-weekday differences of volatile organic compounds (VOCs) and nitrogen oxides (NO + NO2 = NOx) emissions, which induce urban ozone (O3) pollution and sec-ondary organic aerosol (SOA) in fine particulate (with aerodynamic diameters <= 2.5 mu m; PM2.5). However, in-fluences of weekend-weekday differences in primary emissions on the production of secondary pollutants remain unknown. The TROPOspheric Monitoring Instrument and surface observations are carried to simultaneously monitor VOCs, NO2, O3, and PM2.5 concentrations in urban Zhengzhou, China during the weekend and the weekday. Reductions in anthropogenic activities result in atmospheric VOCs and NO2 reductions during the weekend. The ratios of formaldehyde columns to NO2 columns during the weekend afternoon and the weekday afternoon (0.53 and 0.39, respectively) are less than 2.30, indicating the O3 formation under the VOC-limited regime. Lower total VOCs (TVOCs) mixing ratios but higher ratios of TVOCs mixing ratios to NO2 mixing ra-tios during the weekend afternoon perform faster photochemical O3 production. In contrast, higher TVOCs mixing ratios are responsible for higher SOA formation during the weekday. Based on the positive matrix factorization model and VOCs reactivities, solvent usage, vehicle exhaust, and industrial sources are majorly responsible for SOA (80.1%) and O3 (79.9%) formation potential. To reduce O3 concentrations during the weekend and SOA concentrations during the weekday collaboratively, solvent, vehicle, and industrial activities should be transformed from weekday to weekend.

Automated summary

Periodical changes of human activities lead to weekend-weekday differences in volatile organic compounds (VOCs) and nitrogen oxides (NO + NO2 = NOx) emissions, resulting in urban ozone (O3) pollution and secondary organic aerosol (SOA) in fine particulate matter (PM2.5). The influence of differences in primary emissions between weekends and weekdays on the production of secondary pollutants is still unknown. This study used the TROPOspheric Monitoring Instrument and surface observations to monitor VOCs, NO2, O3, and PM2.5 concentrations in urban Zhengzhou, China during weekends and weekdays. The results showed that reductions in anthropogenic activities during weekends led to decreases in atmospheric VOCs and NO2. The ratios of formaldehyde columns to NO2 columns were less than 2.30 during both weekends and weekdays, indicating the O3 formation under VOC-limited conditions. Lower total VOCs (TVOCs) mixing ratios but higher ratios of TVOCs mixing ratios to NO2 mixing ratios during weekends promoted faster photochemical O3 production. In contrast, higher TVOCs mixing ratios were responsible for higher SOA formation during weekdays. Solvent usage, vehicle exhaust, and industrial sources were found to be major contributors to SOA (80.1%) and O3 (79.9%) formation potential based on the positive matrix factorization model and VOCs reactivities. To reduce O3 concentrations during weekends and SOA concentrations during weekdays, solvent, vehicle, and industrial activities should be shifted from weekdays to weekends.