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.

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.

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.

Physical and chemical properties of submicrometer aerosol particles were measured in summer 2004 (June/July) and winter 2005 (January/February) in Beijing, Peoples Republic of China, using a Twin-Differential Mobility Particle Sizer (T-DMPS), a Hygroscopicity-Tandem Differential Mobility Analyzer (H-TDMA), and a Micro Orifice Uniform Deposit Impactor (MOUDI). Particle number-size distributions were measured in the diameter range Dp=3-800 nm and hygroscopic properties were determined at initial dry particle diameters of Dp(j) (j =30, 50, 80, 150, 250, and 350 nm) at a relative humidity (RH) of 90%. Hygroscopic properties were compared with chemical analyses of aerosol samples taken with the MOUDI. Based on the hygroscopicity data, the total hygroscopic particle volume was modeled, including dependence on dry particle size, season and level of pollution using a simple approach. Overall, the chemical analysis showed ammonium sulfate to be the major inorganic component of the urban submicrometer aerosol in Beijing along with relatively high fractions of elemental carbon (10-25%) and organic matter (15-60%) depending on particle size and season. The hygroscopic growth distributions (H-TDMA) subdivided the aerosol population into three different groups of particles with varying growth factors depending on dry particle size, namely nearly hydrophobic (growth factor=0.96-1.07), less hygroscopic (1.06-1.29) and more hygroscopic (1.26-1.62). Hydrophobic particle fractions indicating freshly emitted soot/carbonaceous particles varied between 10 and 32% depending on dry particle size and season. During heavily polluted times, a decreasing number of hydrophobic particle fractions indicated that the urban submicrometer aerosol in Beijing was highly influenced by more aged aerosol transported from the industrial regions around Beijing containing sulfate as a major component. Based on model calculations, the urban submicrometer aerosol in Beijing showed strong compositional variations. The calculated total hygroscopic volume fractions varied between 16 and 65% depending on size, level of pollution and season. (C) 2008 Elsevier Ltd. All rights reserved.

The Campaigns of Air Quality Research in Beijing and Surrounding Region 2006 (CAREBeijing-2006) were mainly focused on the influence of the regional aerosol on the air pollution in Beijing. The urban aerosol was characterized in detail. The particle size distributions were also compared to those measured at a regional site (Yufa) approximately 50 km south of the urban site at Peking University (PKU). At PKU, total particle number and volume concentrations were (1.8 +/- 0.8) x 10(4) cm(-3) and 83.5 +/- 57.9 mu m(3) cm(-3), respectively. Days in three consecutive summers of 2004, 2005, and 2006 were classified as polluted days with PM10 over 150 mu g m(-3) and nonpolluted days with lower PM10. On nonpolluted days, particle number size distributions showed a maximum at about 60 nm with Aitken mode particles dominating number concentration. On polluted days, the contribution of accumulation mode particles increased, shifting the maximum of the number size distribution to over 80 nm. On polluted days with stagnant meteorological conditions, secondary aerosol dominated, with SO42-, NO3-, and NH4+ accounting for over 60% of accumulation mode particle mass. Particle number size distributions at both sites were similar. Number and volume concentrations of total particles at Yufa were 6% and 12% lower, respectively; those of accumulation mode particles were 2% and 15% lower. This means that air pollution in Beijing is mainly a regional problem. The regional accumulation mode particles are a metric for assessing the air quality since they influence most the visibility and total mass concentration. Their number and volume concentrations on polluted days were 5 x 10(3) cm(-3) and 30 mu m(3) cm(-3), respectively. Five new particle formation (NPF) events with continuous smooth growth were observed at both PKU and Yufa during CAREBeijing-2006. These NPF events are regional or semiregional. Growth rates at PKU ranged from 1.2 to 5.6 nm h(-1), and formation rates ranged from 1.1 to 22.4 cm(-3) s(-1). SO42-, NH4+, and oxalate might be important contributors to NPF events.

An aerodyne high-resolution time-of-flight aerosol mass spectrometer (HR-ToF-AMS) combined with a thermodenuder (TD) was used to investigate laboratory-generated aerosol particles with regard to their volatility and chemical content. The performance of the setup was tested first by using ammonium sulfate particles. Organic compounds have been measured including humic acid, fulvic acid, succinic acid and its disodium salt, 2-methylsuccinic acid, fumaric acid, alpha-ketoglutaric acid, and glutaric acid. Among them, humic acid, fulvic acid, and disodium succinate show a non-volatile fraction at 300 degrees C, while the other organic compounds are more volatile. Comparisons of mass spectra at different temperatures showed that significant differences in mass spectra of humic and fulvic acids are observed, indicating that their molecules changed during or after volatilization. At lower temperatures, the changes in humic acid are more likely due to the evaporation of small organic molecules or decomposition of aliphatic groups. The mass losses of the CO(2)(+) fragment for both humic and fulvic acids at higher temperatures may arise from decarboxylation processes. The different mass spectra for humic and fulvic acids before and after TD also suggest that one should be careful in interpretation of volatility measurements because some molecule structures may change after being heated, especially for the non-volatile multifunctional compounds. (C) 2009 Elsevier Ltd. All rights reserved.

In the summers of 2002-2003, acidic gases, ammonia and water-soluble ions in PM10 were measured in Beijing. The mean concentrations of HCl, HONO, HNO3, SO2 and NH3 are 0.6, 3.6, 1.9, 14.1 and 16.6 mu g m(-3), respectively, and 2.2, 14.6, 19.3 and 8.9 mu g m(-3) for Cl-, NO-, SO2- and NH4+ in PM10. The concentrations of secondary ions in PM10 are found to have strong dependence on the pathway of trajectories. The most frequent southerly air flow is connected with high concentrations of secondary water-soluble ions during summertime. Other trajectories with northwest and north direction lead to lower concentrations of secondary ions. Hebei and Shandong Provinces and the Tianjin Municipality are the main source areas for sulfate as identified by Potential Source Contribution Function. This result emphasizes that the non-Beijing sources play an important role in the sulfate mass concentration in the urban atmosphere of Beijing and validates conclusions based on model calculations for the region. (C) 2009 Elsevier Ltd. All rights reserved.

This study was part of the international field measurement Campaigns of Air Quality Research in Beijing and Surrounding Region 2006 (CAREBeijing-2006). We investigated a new particle formation event in a highly polluted air mass at a regional site south of the megacity Beijing and its impact on the abundance and properties of cloud condensation nuclei (CCN). During the 1-month observation, particle nucleation followed by significant particle growth on a regional scale was observed frequently (similar to 30%), and we chose 23 August 2006 as a representative case study. Secondary aerosol mass was produced continuously, with sulfate, ammonium, and organics as major components. The aerosol mass growth rate was on average 19 mu g m(-3) h(-1) during the late hours of the day. This growth rate was observed several times during the 1-month intensive measurements. The nucleation mode grew very quickly into the size range of CCN, and the CCN size distribution was dominated by the growing nucleation mode ( up to 80% of the total CCN number concentration) and not as usual by the accumulation mode. At water vapor supersaturations of 0.07-0.86%, the CCN number concentrations reached maximum values of 4000-19,000 cm(-3) only 6-14 h after the nucleation event. During particle formation and growth, the effective hygroscopicity parameter kappa increased from about 0.1-0.3 to 0.35-0.5 for particles with diameters of 40-90 nm, but it remained nearly constant at similar to 0.45 for particles with diameters of similar to 190 nm. This result is consistent with aerosol chemical composition data, showing a pronounced increase of sulfate.

Two-year measurements of particle number size distribution (3 nm-10 mu m) were conducted in Beijing, China since March 2004. Their seasonal, weekly and diurnal variations and dependencies on meteorological parameters were investigated. The annual average particle number concentrations of the nucleation mode (3-20 nm), Aitken mode (20100 nm), and accumulation mode (0.1-1 mu m) are 9000 cm(-3), 15,900 cm(-3), and 7800 cm(-3), respectively. Particle number concentrations in Beijing are generally higher than that in cities of developed countries, especially for the accumulation mode particles. Both the highest total particle number concentration and the lowest volume concentration occurred in spring due to the frequent nucleation events. However, the minimum particle number concentration was observed in summer, and the maximum volume concentration in fall. The diurnal variation of the nucleation mode particles was mainly influenced by nucleation events, primarily in spring and winter. The diurnal variation of number concentration of the Aitken mode particles closely correlates with the traffic densities in all the four seasons. At the same time, obvious contribution of the growth of the nucleation mode to the number concentration of the Aitken mode particle has been also found in spring, Summer, and fall. Significant differences in diurnal patterns of particle number concentrations between workdays and weekends are not observed in Beijing. Local wind speed plays an important role in shaping the particle number size distributions in the urban area of Beijing. With increasing wind speed, the nucleation and coarse mode particle number concentrations increase, while the number concentrations of the Aitken mode and accumulation mode particles decrease. A "U-shape relationship" between the total particle volume concentration and wind speed is observed. Frequently low wind speed (lower than 3 m s(-1)) in Beijing is one of key factors leading to the poor air quality and low visibility. (C) 2008 Elsevier Ltd. All rights reserved.

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, O-3; 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 x 10(7) to 2.17 x 10(8) molecules cm(-3), the corresponding source rate via reaction of OH and SO2 range between 2.37 x 10(6) and 1.16 x 10(7) 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 x 10(8) to 2.80 x 10(8) molecules cm(-3) with corresponding source rate between 7.26 x 10(6) and 1.64 x 10(7) 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%.

Real-time measurements of acidic trace gases (HCl, HNO(3), HONO, and SO(2)), ammonia, and water-soluble ions in PM(2.5) were conducted at Xinken, a coastal site downwind of Guangzhou, from 4 October to 4 November 2004, as part of the Pearl River Delta (PRD) intensive field campaign. The average concentrations of HCl, HONO, HNO(3), SO(2), and NH(3) are 2.8, 2.9, 6.3, 55.4, and 7.3 mu g m(-3) respectively, and 2.4, 7.2, 24.1, and 9.2 mu g m(-3) for Cl(-), NO(3)(-), SO(4)(2-), and NH(4)(+) in PM(2.5). The diurnal variations of both HCl and HNO(3) showed higher concentrations during daytime and lower concentrations at night, and aerosol Cl(-) and NO(3)(-) showed an opposite diurnal patterns to HCl and HNO(3). The diurnal variation of NH(3) showed the similar pattern to that of aerosol NH(4)(+) with lower concentration during daytime and higher concentration at night. The average concentration of SO(2) during daytime was higher than that at night. The transportation of urban plumes to the sampling site could explain the higher concentration of SO(2) during daytime. HONO showed a clear diurnal variation with lower concentration during daytime and higher concentration at night. The HONO concentrations were positively correlated with the particle surface area concentrations, suggesting the formation of HONO through the heterogeneous conversion on particle surfaces could be significant. The ionic charge balance analysis included the cations derived from filter measurements indicates that the contribution of the cations in fine particle (PM(1.8)) to the charge balance is not pronounced. The theoretical equilibrium constant (K(e)) of NH(4)NO(3) is higher than the observed concentration product (K(m) = [NH(3)] x [HNO(3)]) during daytime, and lower than K(m) at night. This indicates that the atmospheric conditions during the sampling period did not favor the formation of NH(4)NO(3) during daytime. (c) 2008 Elsevier Ltd. All rights reserved.

Continuous measurements of aerosol number size distribution in the range of 3 nm-10 mu m were performed in Pearl River Delta (PRD), China. These measurements were made during the period of 3 October to 5 November in 2004 at rural/coastal site, Xinken (22 degrees 37'N, 113 degrees 35'E, 6m above sea level), in the south suburb of Guangzhou City (22 degrees 37'N, 113 degrees 35'E, 6m abovesea level), using a Twin Differential Mobility Particle Sizer (TDMPS) combined with an Aerodynamic Particle Sizer (APS). The aerosol particles at Xinken were divided into four groups according to the observation results: nucleation mode particles (3-30 nm), Aitken mode particles (30-130 nm), accumulation mode particles (130-1000 nm) and coarse mode particles (1-10 mu m). Concentrations of nucleation mode, Aitken mode and accumulation mode particles were observed in the same order of magnitude (about 10,000 cm(-3)), among which the concentration of Aitken mode particle was the highest. The Aitken mode particles usually had two peaks: the morning peak may be caused by the land-sea circulation, which is proven to be important for transporting aged aerosols back to the sampling site, while the noon peak was ascribed to the condensational growth of new particles. New particle formation events were found on 7 days of 27 days, the new particle growth rates ranged from 2.2 to 19.8 nm h(-1) and the formation rates ranged from 0.5 to 5.2 cm(-3) s(-1), both of them were in the range of typical observed formation rates (0.01-10 cm(-3) s(-1)) and typical particle growth rates (1-20 nm h(-1)). The sustained growth of the new particles for several hours under steady northeast wind indicated that the new particle formation events may occur in a large homogeneous air mass. (c) 2008 Elsevier Ltd. All rights reserved.

Size distributions and particle number concentrations of atmospheric aerosols in the size (diameter) range from 15 mn to 10 mu m were measured on board of a research ship during three cruises in China adjacent seas. The total particle number concentrations were in average around 4000 cm(-3) in Yellow Sea, 2000 cm(-3) in East China Sea and 1000 cm(-3) in South China Sea. The observed size distributions were fitted with two or three log-normal modes and the data were classified according to time, regions and calculated air mass back-trajectories. The size distribution spectra of air masses of polluted continental origin as their back-trajectories showed were characterized by single mode with total number concentrations between 1000 and 10000 cm(-3). The size distributions in marine air masses showed dual mode characteristics, one maximum at 40-60 nm and the other at 160-190 nm with total number concentrations below 1000 cm(-3). This type of dual mode was more pronounced at longer residence time of the air masses over the ocean. The burst of ultra-fine (UF) particles and the consequent growth processes were observed twice in Yellow Sea and possible reasons leading to these events are discussed. The particle growth rate (GR) was 3.4 +/- 0.9 and 3.5 +/- 1.6 nm h(-1), respectively (95% confidence interval), indicating that the UF particles can grow to cloud condensation nuclei (CCN) within the next 1-2 days.) (C) 2007 Elsevier Ltd. All rights reserved.

Particle number size distributions between 3 nm and 10 mm were measured in Beijing, China. New particle formation events were observed on around 40% of the measurement days from March 2004 to February 2005 and were generally observed under low relative humidity and sunny conditions. Though occurring during all seasons, new particle formation events had highest frequency in spring and lowest frequency in summer. Events were classified as "clean'' or "polluted'' groups mainly according to the condensational sink and the local wind. The formation rate range was from 3.3 to 81.4 cm(-3) s(-1). The growth rate varied from 0.1 to 11.2 nm h(-1). The seasonal variation of condensable vapor concentration showed the highest values during summer months due to enhanced photochemical and biological activities as well as stagnant air masses preventing exchange with cleaner air.