The roles of sulfuric acid in new particle formation and growth in the mega-city of Beijing
1State Key Joint Laboratory of Environmental Simulation and Pollution Control, College of Environmental Sciences and Engineering, Peking University, Beijing 100871, China
2Department of Atmospheric Science, Texas A&M University, College Station, Texas 77843, USA
3Leibniz Institute for Tropospheric Research, Permoserstrasse 15, Leipzig 04318, Germany
4Key Laboratory for Urban Habitat Environmental Science and Technology, Shenzhen Graduate School of Peking University, Shenzhen 518055, China
Abstract. Simultaneous measurements of gaseous sulfuric acid and particle number size distributions were performed to investigate aerosol nucleation and growth during CAREBeijing-2008. The analysis of the measured aerosols and sulfuric acid with an aerosol dynamic model shows the dominant role of sulfuric acid in new particle formation (NPF) process but also in the subsequent growth in Beijing. Based on the data of twelve NPF events, the average formation rates (2–13 cm−3 s−1) show a linear correlation with the sulfuric acid concentrations (R2=0.85). Coagulation seems to play a significant role in reducing the number concentration of nucleation mode particles with the ratio of the coagulation loss to formation rate being 0.41±0.16. The apparent growth rates vary from 3 to 11 nm h−1. Condensation of sulfuric acid and its subsequent neutralization by ammonia and coagulation contribute to the apparent particle growth on average 45±18% and 34±17%, respectively. The 30% higher concentration of sulfate than organic compounds in particles during the seven sulfur-rich NPF events but 20% lower concentration of sulfate during the five sulfur-poor type suggest that organic compounds are an important contributor to the growth of the freshly nucleated particles, especially during the sulfur-poor cases.