Submicron aerosols at thirteen diversified sites in China: size distribution, new particle formation and corresponding contribution to cloud condensation nuclei production

摘要

Understanding the particle number size distributions in diversifiedatmospheric environments is important in order to design mitigationstrategies related to submicron particles and their effects on regional airquality, haze and human health. In this study, we conducted 15 differentfield measurement campaigns between 2007 and 2011 at 13 individual sites inChina, including five urban sites, four regionalsites, three coastal/background sitesand one ship cruise measurement along eastern coastline of China. Sizeresolved particles were measured in the 15–600 nm size range. The medianparticle number concentrations (PNCs) were found to vary in the range of1.1−2.2 × 10 cm at urban sites,0.8−1.5 × 10 cm at regional sites,0.4−0.6 × 10 cm at coastal/background sites, and0.5 × 10 cm during cruise measurement. Peak diametersat each of these sites varied greatly from 24 to 115 nm. Particles in the15–25 nm (nucleation mode), 25–100 nm (Aitken mode) and 100–600 nm(accumulation mode) range showed different characteristics at each sites,indicating the features of primary emissions and secondary formation in thesediversified atmospheric environments. Diurnal variations show a build-up ofaccumulation mode particles belt at regional sites, suggesting thecontribution of regional secondary aerosol pollution. Frequencies of newparticle formation (NPF) events were much higher at urban and regional sitesthan at coastal sites and during cruise measurement. The average growth rates (GRs)of nucleation mode particles were 8.0–10.9 nm h at urban sites,7.4–13.6 nm h at regional sites and 2.8–7.5 nm h atcoastal sites and during cruise measurement. The high gaseous precursors and strongoxidation at urban and regional sites not only favored the formation ofparticles, but also accelerated the growth rate of the nucleation modeparticles. No significant difference in condensation sink (CS) during NPFdays were observed among different site types, suggesting that the NPF eventsin background areas were more influenced by the pollutant transport. Inaddition, average contributions of NPF events to potential cloud condensationnuclei (CCN) at 0.2% super-saturation in the afternoon of all samplingdays were calculated as 11% and 6% at urban sites and regional sites,respectively. On the other hand, NPF events at coastal sites and during cruisemeasurement had little impact on potential production of CCN. This studyprovides a large data set of particle size distribution in diversifiedatmosphere of China, improving our general understanding of emission,secondary formation, new particle formation and corresponding CCN activity ofsubmicron aerosols in Chinese environments.