| Presentations and Publications
Zhang, Q., Stanier, C., Caragaratna, M., Jayne, J.T., Worsnop, D., Pandis, S.N., Jimenez, J.L., “Insights into the Chemistry of Nucleation Bursts and Particle Growth Events in Pittsburgh Based on Aerosol Mass Spectrometry.” Environmental Science and Technology, Vol 38(18), 2004, pp. 4797-4809.
New particle formation and growth events have been
observed in several urban areas and are of concern due
to their potential negative effects on human health. The main purpose of this study was to investigate the chemistry of
ultrafine particles during the growth phase of the frequently
observed nucleation events in Pittsburgh (100 events
per year) and therefore infer the mechanisms of new particle
growth in the urban troposphere. An Aerodyne aerosol
mass spectrometer (AMS) and two SMPS systems were
deployed at the U.S. EPA Pittsburgh Supersite during
September 2002. Significant nucleation events were observed
in 3 out of the 16 days of this deployment, including one
of the 10 strongest nucleation events observed in Pittsburgh
over a period of 15 months. These events appear to be
representative of the climatology of new particle formation
and growth in the Pittsburgh region. Distinctive growth
of sulfate, ammonium, organics, and nitrate in the ultrafine
mode (33-60nmin a vacuum aerodynamic diameter or18-
33 nm in physical diameter) was observed during each
of these three events, with sulfate always being the first
(and the fastest) species to increase. Ultrafine ammonium
usually increased 10-40 min later than sulfate, causing
the ultrafine mode particles to be more acidic during the
initial stages of the nucleation events. Significant increase
of ultrafine organics often happened after 11:00 a.m.,
when photochemistry is more intense. This observation
coupled with a parallel increase of ultrafine m/z 44, a mass
fragment generally representative of oxygenated organic
compounds, indicates that secondary organic species
contribute significantly to the growth of particles at a
relatively later time of the event. Among all these four species,
nitrate was always a minor component of the ultrafine particles and contributed the least to the new particle
growth.
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