Nucleation Events During the Pittsburgh Air Quality Study: Description and Relation to Key Meteorological, Gas Phase, and Aerosol Parameters Special Issue of Aerosol Science and Technology on Findings from the Fine Particulate Matter Supersites Program

During the Pittsburgh Air Quality Study (PAQS) aerosol size distributions between 3 nm and 680 nm were measured between July 2001 and June 2002. These distributions have been analyzed to assess the importance of nucleation as a source of ultrafine particles in Pittsburgh and the surrounding areas. The analysis shows nucleation on 50% of the study days and regional-scale formation of ultrafine particles on 30% of the days. Nucleation occurred during all seasons, but it was most frequent in fall and spring and least frequent in winter. Regional nucleation was most common on sunny days with below average PM2.5 concentrations. Local nucleation events were usually associated with elevated SO2 concentrations. The observed nucleation events ranged from weak events with only a slight increase in the particle number to relatively intense events with increases of total particle counts between 50,000 cm−3 up to 150,000 cm−3. Averaging all days of the study, days with nucleation events had number concentrations peaking at around noon at about 45,000 cm−3. This is compared to work days without nucleation, when the daily maximum was 8 am at 23,000 cm−3, and to weekends without nucleation, when the daily maximum was at noon at 16,000 cm−3. Twenty-four-hour average number concentrations were approximately 40% higher on days with nucleation compared to those without. Nucleation was typically observed starting around 9 am EST, although the start of nucleation events was later in winter and earlier in summer. The nucleation events are fairly well correlated with the product of [UV intensity * SO2 concentration] and also depend on the effective area available for condensation. This indicates that H2SO4 is a component of the new particles. Published correlations for nucleation by binary H2SO4—H2O cannot explain the observed nucleation frequency and intensity, suggesting that an additional component (perhaps ammonia) is participating in the particle formation.

[1]  P. Mcmurry,et al.  Recent progress in understanding particle nucleation and growth , 1997 .

[2]  A. G. Sutugin,et al.  Highly Dispersed Aerosols (Vysokodispersne Aerozoli) , 1971 .

[3]  S. Warren,et al.  Oceanic phytoplankton, atmospheric sulphur, cloud albedo and climate , 1987, Nature.

[4]  P. Mcmurry,et al.  New Particle Formation in the Remote Troposphere: A Comparison of Observations at Various Sites , 1999 .

[5]  J Schwartz,et al.  Is daily mortality associated specifically with fine particles? , 1996, Journal of the Air & Waste Management Association.

[6]  R. Harrison,et al.  Continuous measurements of aerosol physical properties in the urban atmosphere , 1999 .

[7]  Roy M. Harrison,et al.  Measurements of the physical properties of particles in the urban atmosphere , 1999 .

[8]  L. Pirjola,et al.  Stable sulphate clusters as a source of new atmospheric particles , 2000, Nature.

[9]  Anthony S. Wexler,et al.  Modelling urban and regional aerosols—I. model development , 1994 .

[10]  Ü. Rannik,et al.  Overview of the international project on biogenic aerosol formation in the boreal forest (BIOFOR) , 2001 .

[11]  Pasi Aalto,et al.  Aerosol formation: Atmospheric particles from organic vapours , 2002, Nature.

[12]  C. N. Hewitt,et al.  Observations of new particle production in the atmosphere of a moderately polluted site in eastern England , 2000 .

[13]  V. Kerminen.  ROLES OF SO2 AND SECONDARY ORGANICS IN THE GROWTH OF NANOMETER PARTICLES IN THE LOWER ATMOSPHERE , 1999 .

[14]  A. Wexler,et al.  A hypothesis for growth of fresh atmospheric nuclei , 2002 .

[15]  R. Kamens,et al.  Atmospheric secondary aerosol formation by heterogeneous reactions of aldehydes in the presence of a sulfuric acid aerosol catalyst. , 2001, Environmental science & technology.

[16]  Roy M. Harrison,et al.  Sources and concentration of nanoparticles (<10 nm diameter) in the urban atmosphere , 2001 .

[17]  A. Peters,et al.  Respiratory effects are associated with the number of ultrafine particles. , 1997, American journal of respiratory and critical care medicine.

[18]  Da-Ren Chen,et al.  Measurement of Atlanta Aerosol Size Distributions: Observations of Ultrafine Particle Events , 2001 .

[19]  C. O'Dowd,et al.  Coupling sea‐salt and sulphate interactions and its impact on cloud droplet concentration predictions , 1999 .

[20]  R. Harrison,et al.  Nanoparticle formation in marine airmasses: contrasting behaviour of the open ocean and coastal environments , 1999 .

[21]  L. Pirjola,et al.  FORMATION OF SULPHURIC ACID AEROSOLS AND CLOUD CONDENSATION NUCLEI: AN EXPRESSION FOR SIGNIFICANT NUCLEATION AND MODEL COMPRARISON , 1999 .

[22]  C. F. Rogers,et al.  Derivation of contributions of sulfate and carbonaceous aerosols to cloud condensation nuclei from mass size distributions , 1996 .

[23]  C. Stanier,et al.  A Method for the In Situ Measurement of Fine Aerosol Water Content of Ambient Aerosols: The Dry-Ambient Aerosol Size Spectrometer (DAASS) Special Issue of Aerosol Science and Technology on Findings from the Fine Particulate Matter Supersites Program , 2004 .

[24]  B. Weiss,et al.  Association of particulate air pollution and acute mortality: involvement of ultrafine particles? , 1995, Inhalation toxicology.

[25]  J. Penner,et al.  Large contribution of organic aerosols to cloud-condensation-nuclei concentrations , 1993, Nature.

[26]  J. Seinfeld,et al.  Effect of NO 2 on Particle Formation in SO 2 /H 2 O/Air Mixtures by Ion-Induced and Homogeneous Nucleation , 2002 .

[27]  Alfred Wiedensohler,et al.  Atmospheric particle number size distribution in central Europe: Statistical relations to air masses and meteorology , 2001 .