| 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%. |
