As part of EPRI's Aerosol Research Inhalation EpidemiologyStudy (ARIES), measurements of aerosol size distributions in the 3 nm to 2 ¹m diameter range were carried out over a 24 month period beginning August 1998 in Atlanta, GA. An automated ne particle sampling system was developed for this study. The sampling system utilizes a nano-scanning mobility particle sizer (3 nm < D p < 50 nm), a standard scanning mobility particle sizer (20 nm < D p < 0.25 ¹m), and a laser particle counter (0.1 ¹m < D p < 2 ¹m). Five complete size distributions are obtained every hour.This paper describes the data collected in the rst 13 month period. The year-long data provide detailed information on temporal variations of aerosol size distributions. Our measurements show that particle number concentrations tend to be higher on weekdays than on weekends. Concentrations of particles in the 10 -100 nm and 100 -2000 nm diameter ranges are higher at night than during the daytime and tend to reach their highest values during morning rush hour. Concentrations of 4 -10 nm particles were elevated during rush hour when temperatures were <10 ± C. Annual average concentrations of particles in the 3 -10 nm diameter range peak between 11 a.m. and 2 p.m. due to the appearance of very high concentrations at those times on a few days. We believe these high concentrations resulted from nucleation. We have identi ed three types of "ultra ne particle" events. On 23 days during August and April we observed events where pronounced peaks in the 3 -10 nm size range occurred. These events typically occurred around noon, when solar radiation was high. During winter months, we occasionally observed signi cantly elevated concentrations in the 10 -35 nm diameter range. These events occurred during early morning and late afternoon hours. Relatively high number concentrations in the 35 -45 nm diameter range were also detected several times. Elevated concentrations of SO 2 were observed during all three types of events. NO x was typically depleted during the 3 -10 nm events and was more likely to be elevated during the 10 -35 and 35 -45 nm events. The sources of these particles are not yet known.

No abstract

No abstract

The formation of new atmospheric particles by gas-to-particle conversion leads to enhanced concentrations of nanoparticles. We have studied the formation and growth of new particles in urban Atlanta and in the remote atmosphere in locations ranging from the North Pole to Mauna Loa, Tasmania and the South Pole. Key to this work was our development of new measurement techniques for freshly formed nucleation mode particles between 3 and 10 nm. In this paper we show that measured aerosol size distributions in the 3{10 nm diameter range often increase with decreasing size down to our minimum detectable size of 3 nm, presumably because nucleation was occurring during the measurement. Furthermore, we show that the Atlanta nucleation mode size distributions are consistent with a collision-controlled nucleation process in which accommodation coe¯cients for all collisions between condensing molecules and molecular clusters and between molecular clusters are assumed to be equal to one, and in which evaporation from molecular clusters is neglected, as would be expected for a highly supersaturated vapour.

Size distributions of urban Atlanta, Georgia, aerosols (0.003-2 microm) were measured from August 1, 1998 through August 30, 2000 as part of the Aerosol Research Inhalation Epidemiology Study (ARIES). Size distributions were measured five times per hour, and approximately 50,000 size distributions were measured during the 25-month study. This paper focuses on salient features of the sub-100-nm data. We examine concentrations of particles in six equally spaced logarithmic intervals and show that particles of different sizes have distinctly different behaviors. For particles between 10 and 100 nm, average concentrations tended to be highest during winter, during rush hour, and on week days. Concentrations of particles in the 3-10-nm range were elevated in the summer due to photochemically driven nucleation, and also during winter. We hypothesize that the elevated wintertime concentrations of these particles were associated with nucleation that occurs as vehicular emissions mix with the cool ambient air. In any given size range, distributions of concentrations tend to be lognormal, but significant deviations from lognormality were occasionally observed. For particles in the 3.2-5.6-nm diameter range, deviations were apparent in the summer when very high concentrations (up to 10(6) cm(-3)) were produced by photochemically driven nucleation. During 2 months of the study, deviations from lognormality for particles in the 32-56-nm diameter range occurred when anomalously high concentrations of 40-nm particles were observed.