Mobile measurements of atmospheric decamethylcyclopentasiloxane (D5) in Eastern China

Decamethylcyclopentasiloxane (D5) is prevalent in European and North American urban air due to the use of personal care products. China accounts for 55% of global siloxane production, yet the atmospheric concentration and sources of D5 in China remain largely unexplored. Using the Vocus mobile laboratory, here we performed high time-resolved measurements of D5 along a north-south transect (∼700 km) in eastern China. Prior to reaching the destination, Nanjing Chemical Industry Park (NCIP), D5 concentration had a low variability of minute-mean concentration (2.6 ± 1.3 pptv). Population density didn't exhibit a correlation with D5 concentration (1-min average concentration) (R² = 0.06), whereas a significant correlation was observed between the city-scale population and D5 concentration (R² = 0.74). Concentrated spikes in D5 concentrations (peaking at 384.8 pptv per second) were observed around NCIP, home to nearly 400 energy and chemical companies. These D5 concentrations were highly correlated with agrochemical-related dichlorobenzenes (R² = 0.99) rather than other petrochemical-related tracers. Unlike developed countries, D5 in China's air may primarily originate from emissions released during production processes.