Regional Nucleation Events and Sources of Submicron Particles in Rochester (NY)

Extensive measurements of particle number concentration (PNC) and particle size distribution (PNSD) have been performed in Rochester (NY) since 2001. These long-term data allow assessment of past and current mitigation strategies for air pollution in the Northeastern US. This study investigates the three most recent years of data (2014/16). Results show an average of 4.3·103 particles/cm3, of which 1.4·103, 2.3·103, and 0.7·103 particles cm3 were classified as nucleation (14-30 nm), Aitken nuclei (30-100 nm) and accumulation (100-470 nm) ranges, respectively. Annually, total PNC show two maxima, one on February and one during summer (May to September), while the daily pattern of PNC show two peaks related to the traffic rush hours (one in the early morning, one in the late afternoon-evening). Nucleation sized particles also show an evident increase during daytime, which is broadly comparable with the nucleation events driven by photochemical transformations. Positive matrix factorization (PMF) was applied to identify and quantify the major airborne particle sources. Data were separately analyzed for summer, winter, and transition periods. For each period, 5 to 7 factors were apportioned and identified (nucleation, traffic, domestic and residential heating, secondary aerosol and ozone-rich aerosol). The application of PMF post-processing tools was useful to: (i) study the patterns of sources; (ii) depict the role of atmospheric photochemical processes; (iii) examine the locations of potential local sources by mean of conditional bivariate probability function analysis and (iv) investigate the role of regional transport of air masses to the concentrations of resolved sources. Finally, the contour plots of SMPS data were examined: an algorithm was applied to identify potential nucleation events and distinguish them between traffic nucleation events and regional photochemical nucleation events.