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Mass size distributions and size resolved chemical composition of fine particulate matter at the Pittsburgh supersite
Abstract
Size-resolved aerosol mass and chemical composition were measured during the Pittsburgh
Air Quality Study. Daily samples were collected for 12 months from July 2001 to June
2002. Micro-orifice uniform deposit impactors (MOUDIs) were used to collect aerosol
samples of fine particulate matter smaller than 10 mum. Measurements of PM0.056, PM0.10,
PM0.18, PM0.32, PM0.56, PM1.0, PM1.8 and PM2.5 with the MOUDI are available for the
full study period. Seasonal variations in the concentrations are observed for all
size cuts. Higher concentrations are observed during the summer and lower during the
winter. Comparison between the PM2.5 measurements by the MOUDI and other integrated
PM samplers reveals good agreement. Good correlation is observed for PM10 between
the MOUDI and an integrated sampler but the MOUDI underestimates PM10 by 20\%. Bouncing
of particles from higher stages of the MOUDI ( > PM2.5) is not a major problem because
of the low concentrations of coarse particles in the area. The main cause of coarse
particle losses appears to be losses to the wall of the MOUDI. Samples were collected
on aluminum foils for analysis of carbonaccous material and on Teflon filters for
analysis of particle mass and inorganic anions and cations. Daily samples were analyzed
during the summer (July 2001) and the winter intensives (January 2002). During the
summer around 50\% of the organic material is lost from the aluminum foils as compared
to a filter-based sampler. These losses are due to volatilization and bounce-off from
the MOUDI stages. High nitrate losses from the MOUDI are also observed during the
summer (above 70\%). Good agreement between the gravimetrically determined mass and
the sum of the masses of the individual compounds is obtained, if the lost mass from
organics and the aerosol water content are included for the summer. For the winter
no significant losses of material are detected and there exists reasonable agreement
between the gravimetrical mass and the sum of the concentrations of the individual
compounds. Ultrafine particles (below 100 nm) account on average, for
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