Analysis on Concentration and Source Rate of Precursor Vapors Participating in Particle Formation and Growth at Xinken in the Pearl River Delta of China

Abstract: Concentration and source rate of precursor vapors participating in particle formation and subsequent growth were investigated during the Pearl River Delta intensive campaign (PRD2004, October 2004) in southeastern China. Four new particle formation event days and a typical non-event day were selected for our analysis. Atmospheric sulphuric acid, the important precursor vapor in nucleation and growth, were simulated with a pseudo steady-state model based on the measurements of SO2, NOx, O3, CO, non-methane hydrocarbon (NMHC) and ambient particle number concentrations as well as modeled photolysis frequencies obtained from measurements. The maximum midday sulphuric acid concentrations vary from 4.53×107 to 2.17×108 molecules cm-3, the corresponding source rate via reaction of OH and SO2 range between 2.37×106 and 1.16×107 molecules cm-3 s-1. Nucleation mode growth rate was derived from size spectral evolution during the events to be 6.8--13.8 nm h-1. Based on the growth rate, concentration of the vapors participating in subsequent growth were estimated to vary from 1.32×108 to 2.80×108 molecules cm-3 with corresponding source rate between 7.26×106 and 1.64×107 molecules cm-3 s-1. Our results show the degree of pollution is larger in PRD. Sulphuric acid concentrations are fairly high and have a close correlation with new particle formation events. Budget analysis shows that sulphuric acid alone is not enough for required growth; other nonvolatile vapors are needed. However, sulphuric acid plays an important role in growth; the contribution of sulphuric acid to growth in PRD is 12.4%--65.2%.

Keywords:
• particle formation and growth,
• sulphuric acid,
• pseudo steady state model,
• condensation sink,
• precursor vapors,
• source rate