Continuous measurements of aerosol size distributions (3 nm-2 μm) were carried out over a 26 month period (1 April 2001-31 May 2003; 650 days with valid data) in urban East St. Louis, IL, as a part of the US Environmental Protection Agency's Supersite program. This paper analyzes data for the 155 days on which "regional nucleation events" were observed during this study. Such events were observed during every month of the study except January 2003. We observed some differences, however, between events in the summer (defined here as April-September) and winter (December-February). Regional nucleation events were observed more frequently in summer months (36±13% of days) than in winter (8±7%), and nucleated particles grew faster in the summer (6.7±4.8 nm h-1) than in winter (1.8±1.9 nm h-1). The daily maximum in the number concentration of nanoparticles formed by nucleation (4.8±3.5×104 cm-3) was highly variable and showed no clear seasonal dependence. Particle formation increased particle concentrations by an average factor of 3.1±2.8. Maximum daily rates of 3 nm particle production (17±20 cm-3 s-1) were also highly variable and without a clear seasonal dependence. During these events, particle formation rates were typically near their maxima at 08:00-09:00 a.m., but particle production sometimes persisted at diminishing rates until late in the afternoon (15:00-16:00 p.m.).
Bibliographical noteFunding Information:
This research was supported by subcontracts from Washington University, which was the lead institution for the St. Louis Supersite (US Environmental Protection Agency under agreement R-82805901 (first year measurements) and X-98722301 (second year measurements)). Although the research described in this article has been funded wholly or in part by the United States Environmental Protection Agency, it has not been subjected to the Agency's required peer and policy review and therefore does not necessarily reflect the views of the Agency nor official endorsement should be inferred. We also express our appreciation to Professor Jay Turner and members of his research team (Yanhui Yang, Andrea Clements, Jay Hill, Scott Duthie, Megan Yu) for the cheerful help that they provided with operating and providing routine maintenance on our equipment.
Copyright 2008 Elsevier B.V., All rights reserved.
- New particle formation
- Ultrafine aerosol
- Urban aerosol