In order to characterize the features of particulate pollution in the Pearl River Delta (PRD) in the summer, continuous measurements of particle number size distributions and chemical compositions were simultaneously performed at Guangzhou urban site (GZ) and Back-garden downwind regional site (BG) in July 2006. Particle number concentration from 20 nm to 10 mu m at BG was (1.7 +/- 0.8) x 10(4) cm(-3), about 40% lower than that at GZ, (2.9 +/- 1.1) x 10(4) cm(-3). The total particle volume concentration at BG was 94 +/- 34 mu m(3) cm(-3), similar to that at GZ, 96 +/- 43 mu m(3) cm(-3). More 20-100 nm particles, significantly affected by the traffic emissions, were observed at GZ, while 100-660 nm particle number concentrations were similar at both sites as they are more regional. PM(2.5) values were similar at GZ (69 +/- 43 mu g m(-3)) and BG (69 +/- 58 mu g m(-3)) with R(2) of 0.71 for the daily average PM(2.5) at these two sites, indicating the fine particulate pollution in the PRD region to be regional. Two kinds of pollution episodes, the accumulation pollution episode and the regional transport pollution episode, were observed. Fine particles over 100 nm dominated both number and volume concentrations of total particles during the late periods of these pollution episodes. Accumulation and secondary transformation are the main reasons for the nighttime accumulation pollution episode. SO(4)(2-), NO(3)(-), and NH(4)(+) accounted for about 60% in 100-660 nm particle mass and PM(2.5) increase. When south or southeast wind prevailed in the PRD region, regional transport of pollutants took place. Regional transport contributed about 30% to fine particulate pollution at BG during a regional transport case. Secondary transformation played an important role during regional transport, causing higher increase rates of secondary ions in PM(1.0) than other species and shifting the peaks of sulfate and ammonium mass size distributions to larger sizes. SO(4)(2-), NO(3)(-), and NH(4)(+) accounted for about 70% and 40% of PM(1.0) and PM(2.5), respectively.

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 (R-2=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.

The coagulation sink and its role in new particle formation are investigated based on data obtained during the PRIDE-PRD2004 campaign at Xinken of Pearl River Delta, China. Analysis of size distributions and mode contributions of the coagulation sink show that the observed higher load of accumulation mode particles impose a significant effect on the coagulation sink and result in higher coagulation sinks at Xinken despite of the lower total particle number compared with other areas. Hence it is concluded that the higher coagulation sink may depress the occurrence frequency of new particle formation events. The strategies targeting at controlling accumulation mode particles may have influences on the frequency of new particle formation events at this area. The factors affecting the coagulation sink are evaluated. The relatively lower ambient relative humidities may weaken the coagulation sink and facilitate the occurrence of new particle formation events during noontime, while the surmise of nucleation and growth involving organic matter may imply an actually higher coagulation sink than expected. These factors have a significant influence on the ultimate fate of the newly formed nuclei and new particle formation. A comparison of event and non-event days indicates that the coagulation sink is not the only decisive factor affecting new particle formation, other factors including the precursor vapors and photochemical activity are none the less important either. Competition of coagulation sink and high source rate leads to the occurrence of new particle formation events at Xinken. Crown Copyright (C) 2010 Published by Elsevier Ltd. All rights reserved.