Measurement of Atlanta aerosol size distributions: Observations of ultrafine particle events

As part of EPRI's Aerosol Research Inhalation Epidemiology Study (ARIES), m easurements of aerosol size distributions in the 3 nm to 2 mum diameter ran ge were carried out over a 24 month period beginning August 1998 in Atlanta , GA. An automated fine particle sampling system was developed For this stu dy, 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 mum), and a laser particle counter (0.1 mum < D-p < 2 mum), Five c omplete size distributions are obtained every hour, This paper describes the data collected in the first 13 month period, The S car-long data provide detailed information on temporal variations of aeroso l size distributions, Our measurements show that particle number concentrat ions tend to he higher on weekdays than on weekends. Concentrations of part icles 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 morni ng rush hour, Concentrations of 4-10 nm particles were elevated during rush hour when temperatures were <10 C. Annual average concentrations of partic les in the 3-10 nm diameter range peak between 22 a.m, and 2 p.m. due to th e appearance of very high concentrations at those times on a few days, We b elieve these high concentrations resulted From nucleation. We have identifi ed three types of "ultrafine 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 significantly ele vated concentrations in the 10-35 nm diameter range. These events occurred during early morning and late afternoon hours, Relatively high number conce ntrations In the 35-45 nm diameter range were also detected several times. Elevated concentrations of SO2 were observed during all three types of even ts. NO, was typically depleted during the 3-10 nm events and was more likel y to be elevated during the 10-35 and 35-45 nm events. The sources of these particles are not yet known.