Gas/particle partitioning and global distribution of polycyclic aromatic hydrocarbons – A modelling approach

Abstract

a b s t r a c tThe global atmospheric distribution and long-range transport (LRT) potential of three polycyclic aromatic hydrocarbons (PAH) -anthracene, fluoranthene and benzo [a]pyrene -are studied. The model used is a global aerosol-chemistry-transport-model, which is based on an atmospheric general circulation model. The model includes an in-built dynamic aerosol model coupled to two-dimensional surface compartments. Several parameterisations of gas/particle partitioning and different assumptions of degradation in the aerosol particulate phase were tested.PAHs are mostly distributed in the source regions but reach the Arctic and the Antarctic. The Canadian Arctic is predicted to be significantly less affected by mid-latitude PAH emissions than the European Arctic. Re-volatilisation is significant for semivolatile PAHs. Accumulation of semivolatile PAHs in polar regions, however, is not indicated. The model study suggests that gas/particle partitioning in air drastically influences the atmospheric cycling, the total environmental fate (e.g. compartmental distributions) and the LRT potential of the substances studied. A parameterisation which calculates the gas/particle partitioning assuming absorption into organic matter and adsorption to black carbon (soot) agrees best with the observations at remote sites. The study provides evidence that the degradation in the particulate phase must be slower than that in the gas-phase. The predicted concentrations of the semivolatile PAHs anthracene and fluoranthene in near-ground air at remote sites in mid and high northern latitudes are in line with measured concentrations, if adsorption of the substances to soot combined with absorption in particulate organic matter is assumed to determine gas/particle partitioning, but cannot be explained by adsorption alone (Junge-Pankow parameterisation of gas/particle partitioning). The results suggest that PAHs absorbed in the organic matrix of particulate matter is shielded from the gas-phase.

Evaluation of a Conceptual Model for Gas-Particle Partitioning of Polycyclic Aromatic Hydrocarbons Using Polyparameter Linear Free Energy Relationships

“…On the contrary, choosing the lower surface area of 3.6 m 2 g −1 reduced the contribution of adsorption onto soot to ≤2%. The results showed that the contributions from salts were negligible − adsorption to (NH 4 ) 2 SO 4 and NH 4 Cl contributed to <0.1% of the K P ; however, the magnitude of adsorption was much higher for (NH 4 ) 2 SO 4 (a factor of 30 ± 2) than for NH 4 Cl. Overall, the results suggest that adsorption to matrices other than soot may be neglected for modeling PAH gas-particle partitioning.…”

“…53 The minimum and maximum of these surface areas were also applied in order to explore the sensitivity of the model predictions. We acknowledge that the phases considered in the present study may not be fully available for PAH partitioning due to internal mixing and kinetic limitations related to OM phase-state 54 (slow diffusion in semisolid and solid phases) and that under high relative humidity (NH 4 ) 2 SO 4 and NH 4 Cl may be present in dissolved aqueous phase and subject to liquid−liquid phase separation with OM. 55 Moreover, as PM composition varies significantly with particle size, SOC sorption behavior is expected to be particle-size dependent.…”

Seasonal trends and spatial variations of PM10-bounded polycyclic aromatic hydrocarbons in Veneto Region, Northeast Italy

“…Being generally partitioned between the gaseous and particulate phases (e.g. Lammel et al, 2009), the 4-, 5-and 6-ring PAHs are predominantly particle-bound due to their high molecular weights and low volatilities. Despite their well documented toxic potential on humans and ecosystems (e.g.…”

Stability of polycyclic aromatic compounds in polyurethane foam-type passive air samplers upon O3 exposure

“…In the real environment, PACs with more than 4 rings, including reactive BaP, PER, and DahA, are mainly associated with particulate matter (Su et al, 2006;Yamasaki et al, 1982) and hence suffer from O 3 degradation to a lesser extent as they are partially shielded from gaseous oxidants by black carbon, organic matter, and the accumulation of atmospheric reaction products on the surface. (Jariyasopit et al, 2014;Lammel et al, 2009;Zhou et al, 2012) Furthermore, it is Fig. 2.…”