Spatial distributions of secondary organic aerosols from isoprene, monoterpenes,β-caryophyllene, and aromatics over China during summer

Abstract

Filter-based particle samples were simultaneously collected at 14 sites across 6 regions of China during the summer of 2012. These filters were analyzed for secondary organic aerosol (SOA) tracers from biogenic precursors (isoprene, monoterpenes, and β-caryophyllene) and anthropogenic aromatics. The sum of all SOA tracers ranged from 29.9 to 371 ng m−3 with the majority from isoprene (123 ± 78.8 ng m−3), followed by monoterpenes (10.5 ± 6.64 ng m−3), β-caryophyllene (5.07 ± 3.99 ng m−3), and aromatics (2.90 ± 1.52 ng m−3). The highest levels of biogenic SOA tracers were observed in East China, whereas the highest concentrations of the aromatic SOA tracer, 2,3-dihydroxy-4-oxopentanoic acid (DHOPA), occurred in North China. All biogenic SOA tracers exhibited positive correlations with temperature, most likely resulting from enhanced biogenic volatile organic compounds (BVOCs) emissions and photochemistry in high-temperature regions. Among the isoprene SOA tracers, the low-NOx products 2-methyltetrols were the largest by mass concentration. However, at certain urban sites, the contribution of the high-NOx product 2-methylglyceric acid was significantly higher, implying a greater influence of NOx on isoprene SOA formation in urban areas. For the monoterpene SOA tracers, the ratio of the first-generation products (cis-pinonic acid plus pinic acid) to the high-generation product (3-methyl-1,2,3-butanetricarboxylic acid) exhibited a negative correlation with the amount of high-generation products, indicating that this ratio could serve as an indicator of the aging of monoterpene SOA. The ratio ranged from 0.89 to 21.0, with an average of 7.00 ± 6.02, among the observation sites, suggesting that monoterpene SOA was generally fresh over China during the summer. As a typical anthropogenic SOA tracer, DHOPA exhibited higher levels at urban sites than at remote sites. These SOA tracers were further used to attribute SOA origins via the SOA-tracer method. The total concentrations of secondary organic carbon (SOC) and SOA were estimated to be in the range of 0.37 to 2.47 μgC m−3 and 0.81 to 5.44 µg m−3, respectively, with the highest levels observed in the eastern regions of China. Isoprene (46 ± 14%) and aromatics (27 ± 8%) were the two major contributors to SOC in every region. In North China, aromatics were the largest SOA contributor. Our ground-based observations suggest that anthropogenic aromatics are important SOA precursors in China.