Long-range Atmospheric Transport of Polycyclic Aromatic Hydrocarbons is Worldwide Problem - Results from Measurements at Remote Sites and Modelling.

Gerhard Lammel

doi:10.17344/acsi.2015.1387

Abstract

Despite the fact that the occurrence of polycyclic aromatic hydrocarbons (PAHs) in the atmospheric environment has been studied for decades the photochemistry, deposition and, consequently, the long-range transport potential (LRTP) are not well understood. The reason is gas-particle partitioning (GPP) in the aerosol, its sensitivity to temperature and particulate phase composition, and sampling artefacts', and reactivity's sensitivities towards particulate phase composition. Furthermore, most PAHs are subject to re-volatilisation upon deposition to surfaces (multihopping). Levels and sources of 2-6-ring unsubstituted PAHs were studied in remote environments of Europe, Africa and Antarctica. Global atmospheric transport and fate of 3-5-ring PAHs were simulated under various scenarios of photochemistry and GPP. GPP influences drastically the atmospheric lifetime, compartmental distributions and the LRTP of PAH. Mid latitude emissions seem to reach the Arctic but not the Antarctic.

Highlights

Polycyclic aromatic hydrocarbons (PAHs) are unavoidable by-products of any kind of combustion, in particular incomplete combustion processes
Despite the fact that the occurrence of polycyclic aromatic hydrocarbons (PAHs) in the atmospheric environment has been studied for decades the photochemistry, deposition and, the long-range transport potential (LRTP) are not well understood
Levels and sources of 2-6-ring unsubstituted PAHs were studied in remote environments of Europe, Africa and Antarctica

Summary

Introduction

Polycyclic aromatic hydrocarbons (PAHs) are unavoidable by-products of any kind of combustion, in particular incomplete combustion processes. These substances are ubiquitous in the polluted atmospheric environment in the ng m–3 concentration range.[1] The gaseous state is predominant for the lighter relative molecular mass PAHs, while the substances with more than 4 rings are preferentially associated with the aerosol particles.[2,3] Gas-particle partitioning is significant for many PAHs (so-called semivolatility, expected for saturation vapour pressures in ambient air in the range psat = 10–6–10–2 Pa 4). PAHs may undergo long-range transport and reach pristine areas in high altitudes and latitudes.[12,13,14,15] Obviously, rate coefficients for particle bound PAHs determined in the laboratory tend to overestimate atmospheric degradation, most likely as a consequence of matrix effects which so far could not be mimicked in laboratory experiments, i.e. shielding against oxidant attack.[16,17]

Experimental

Results and Discussion

Conclusions

European Commission Polycyclic Aromatic Compounds Working Group