222Rn decay products as tracers of indoor and outdoor aerosol particle size

Measurements of the air concentration of 210Pb indoors and outdoors were made at a single-family suburban home in northern New Jersey over a 1.5 year period. A sampler with 5 fine mesh screens and a backup Millipore filter was used to determine the indoor and outdoor ultrafine particle size distribution. A sample of the total airborne particulates was collected simultaneously. The long-lived 222Rn decay product 210Pb presents a unique and highly sensitive tracer to study atmospheric aerosol particles. The aerosol particle size sampler integrates ultrafine particulates deposited over 3–4 weeks. The measurement of 210Pb (210Po) on the screens and filter was performed using very low background alpha scintillation counters (3–5 counts/day), and long count times (5000 min). Deconvolution of the alpha counting data was performed using an extreme value estimation program (EVE) that provides an accurate evaluation of the particle size distribution. The particle size data show that a significant fraction (20–60%) of the atmospheric aerosol particles in this suburban location are in the ultrafine region. The indoor to outdoor 210Pb ratio revealed that 65% of the outdoor aerosol particles in this suburban location comprise the indoor particle concentration.