Role of PM2.5 in the photodegradation of the atmospheric benzene.

The presence of PM2.5 may affect the photodegradation of benzene in the natural atmosphere. On one hand, the photodegradation of benzene may be promoted with the increase in PM2.5 concentrations, owing to adsorption and catalysis effect of PM2.5 surface; On the other hand, PM2.5 can scatter or block ultraviolet light and lead to weakening the photochemical reactions in the atmospheric system. It is very difficult to prove which process is dominant in the real atmosphere due to the complexity of the atmosphere. Based on coupling detrended fluctuation analysis, the goal of this work is to reveal the role of PM2.5 in the photodegradation of benzene in real atmosphere over long time scales. The 9 years regular monitoring data from 2007 to 2016 in Puzi of Taiwan are analyzed. A new nonlinear parameter (PDB) is established to characterize the photodegradation degree of atmospheric benzene. Based on sliding window technique, the correlations between the temporal variation of PDB and PM2.5 are analyzed. The results show that there is a positive correlation between PDB and PM2.5 in daytime and little correlation between them in nighttime. It indicates that PM2.5 mainly plays the promoting effect on the photodegradation of atmospheric benzene. This is the first study to directly determine the role of PM2.5 in the photochemical behavior of atmospheric benzene based on long term field observation data. Moreover, the results suggest that the regional transport of PM2.5 could seriously affect the geochemistry cycle of some VOCs. This research provides a new analysis method to directly quantify the effect of PM2.5 on the photodegradation of VOCs in the real atmosphere. It is helpful for evaluating the role of PM2.5 in the complex photochemical system.