Spatial and seasonal variations of secondary organic aerosol from terpenoids over China

A majority of global secondary organic aerosol (SOA) comes from terpenoids. In this study, we carried out a 1 year nationwide observation of pinenes (α‐ and β‐pinene) and SOA tracers from monoterpenes (SOAM) and β‐caryophyllene (SOAC) over China for the first time. SOAM and SOAC tracers ranged from 9.80 to 49.0 ng m−3 and 1.72 to 7.72 ng m−3, respectively, with high levels in southern China. Pinenes ranged from 34 to 102 parts per trillion by volume, with α‐pinene dominant over β‐pinene. SOAM tracers were correlated between paired sites, suggesting a regional impact of SOAM, while pinenes were uncorrelated between sites due to their rapid oxidation. High levels of SOAM tracers were observed in spring and summer. However, at the Hailun site in Northeast China, SOAM tracers increased during winter. The positive correlation between SOAM tracers and the biomass burning (BB) tracer levoglucosan during winter at Hailun indicated that the unexpected increase of SOAM was associated with BB. The SOAC tracer, β‐caryophyllenic acid, increased during winter and was positively correlated with levoglucosan, suggesting substantial contributions from BB to SOAC production in wintertime. Together with SOA tracers from isoprene, these tracers were applied to estimate biogenic secondary organic carbon (BSOC) from isoprene, monoterpenes, and β‐caryophyllene. The annual average BSOC was 0.91 ± 0.41 μgC m−3,with the majority from monoterpenes and the highest level in Southwest China. BSOC was elevated from April to September and was lowest in January and February. BSOC composition dramatically changed from a monoterpene majority in fall‐spring to an isoprene majority in summer. Key Points The first nationwide measurements of BSOA tracers showed high concentrations in southern China Unexpected increases of SOA from monoterpenes and β‐caryophyllene during winter were correlated with biomass burning BSOC composition dramatically changed from a monoterpene majority in fall‐spring to an isoprene majority in summer