HR: 0830h
AN: A11E-0027    [PDF]
TI: A Detailed Study of the Chemistry and Mechanisms of Particle Growth during Nucleation Events in a Polluted Urban Area
AU: Jimenez, J
EM: jose.jimenez@colorado.edu
AF: University of Colorado at Boulder, Cooperative Institute for Research in Environmental Sciences (CIRES) 216 UCB, Boulder, CO 80309 United States
AU: * Zhang, Q
EM: zhangq@cires.colorado.edu
AF: University of Colorado at Boulder, Cooperative Institute for Research in Environmental Sciences (CIRES) 216 UCB, Boulder, CO 80309 United States
AU: Stanier, C
EM: cos@andrew.cmu.edu
AF: University of Carnegie Mellon, Department of Chemical Engineering, Pittsburgh, PA 15213-3890 United States
AU: Pandis, S
EM: spyros@andrew.cmu.edu
AF: University of Carnegie Mellon, Department of Chemical Engineering, Pittsburgh, PA 15213-3890 United States
AU: Canagaratna, M C
EM: mrcana@aerodyne.com
AF: Aerodyn Research Inc, 45 Manning Road, Billerica, MA 01821-3976 United States
AU: Jayne, J T
EM: jayne@aerodyne.com
AF: Aerodyn Research Inc, 45 Manning Road, Billerica, MA 01821-3976 United States
AU: Worsnop, D R
EM: worsnop@aerodyne.com
AF: Aerodyn Research Inc, 45 Manning Road, Billerica, MA 01821-3976 United States
AB: New particle formation has been recently observed in several urban areas, and is of concern due to its potentially enhanced negative effects on human health. A recent yearlong ambient study concluded that nucleation occurs on about 50% of the days in Pittsburgh, PA, USA. Since classical binary H2SO4-H2O theory is insufficient to explain the frequency and intensity of these events, it has been suggested that additional species such as ammonia and organic vapors may be involved in the process. In order to test these hypotheses and to investigate the evolution of number, size, and composition of ultrafine particles during the growth of newly formed particle, an Aerodyne Aerosol Mass Spectrometer (AMS), along with two SMPS systems, was operated at the Pittsburgh EPA Supersite in September 2002, as part of the Pittsburgh Air Quality Study (PAQS). Significant nucleation and growth events were observed in three out of the sixteen days of this deployment, including one that is identified as top 10 strongest events in Pittsburgh over a period of 15 months. These events also appear to be representative for the climatology of the formation and growth of the nucleation mode particles in Pittsburgh. The smallest particles that the AMS could detect (~ 14 nm mobility diameter) are estimated to have about 100 times the mass of the initial 3 nm nuclei; therefore chemical composition of fresh particles as determined by the AMS is used to infer the chemistry of particle growth, rather than initial nuclei chemistry. All these events showed distinctive growth of sulfate, ammonium, organics and nitrate in the ultrafine mode. During each of these 3 events, sulfate was always the first, and often the fastest, species to increase in the ultrafine particles. Ultrafine ammonium also increased significantly, but usually lagged by 5 - 10 min behind the increase of sulfate. For this reason the ultrafine particles tended to be acidic during the initial stages of the nucleation event. Substantial increase of ultrafine organics was often observed at late morning or in early afternoon. There is evidence that condensation of photochemically produced secondary organic compounds might be the major mechanism for this increase. We also observed simultaneous rises of ultrafine organics and sulfate during the initial growth phase of the two events. Because the growth of ultrafine organics seemed to slow down when particles became more neutralized, it is possible that these initial growth was due to acid-catalyzed formation of secondary organic aerosol from photochemically produced oxidized organic vapors. Among all these four species, nitrate was always the least important in the growth.
DE: 0305 Aerosols and particles (0345, 4801)
DE: 0345 Pollution--urban and regional (0305)
DE: 0365 Troposphere--composition and chemistry
DE: 0368 Troposphere--constituent transport and chemistry
SC: Atmospheric Sciences [A]
MN: 2003 Fall Meeting