PAH atmospheric log(KP) values in Great Lakes samples are related to black carbon levels near each site

Abstract

Many semi-volatile organic pollutants are present in the atmosphere both in the vapor and particle phases. About 50 years ago, a partition coefficient (KP) was defined as the compound's concentration in the particle phase (Cpart, in ng/m3 or pg/m3) divided by its concentration in the vapor phase (Cvapor, also in ng/m3 or pg/m3) divided by the atmospheric concentration of total suspended particles (TSP, in μg/m3) or, more recently, by the concentration of particulate matter with aerodynamic diameters less than 2.5 μm (PM2.5, also in μg/m3). The original point of this term was to account for surface adsorption of pollutants to the particles, but over the years it has become apparent that absorption, particularly to black carbon (BC, also known as elemental carbon) in the particles, may also be important. This study investigates the importance of this particle term using about 3000 polycyclic aromatic hydrocarbon (PAH) concentrations measured from 1997 to 2018 (inclusive) in 24-h samples collected once every 12 days at five sites on the shores of the North American Great Lakes and using U.S. Environmental Protection Agency PM2.5 concentrations at the same sites. Analyses of variance of the annual mean log(KP) values show significant differences for all six compounds among the five sites, which we attribute to the composition of the particles at the five sites. For example, the particles from the urban sites are likely to have higher black carbon levels compared to those from the more rural and remote sites. With an additional term for black carbon in these samples, these new ratios are similar across sites for a given compound. These results suggest that a black carbon term is useful and potentially important.