An overview of possible processes able to account for the occurrence of nitro-PAHs in Antarctic particulate matter

This paper gives an overview of the processes that can account for the occurrence of mononitro-PAHs (1-nitronaphthalene — 1NN-, 2-nitronaphthalene — 2NN-, 9-nitroanthracene) in the Antarctic particulate matter. Long-range transport of these compounds from the continents to the Antarctica seems an unlikely possibility given the photolability of 1NN and 2NN. The alternative possibility is that nitration takes place in situ. The nitration of naphthalene is very likely to occur in the gas phase, because the parent compound is too volatile to be present in particulate matter, even at the low temperatures of the Antarctic summer near the coast. In contrast, the volatility of anthracene is sufficiently low under such conditions to allow this compound to be present in particles at a significant concentration. The field data on nitronaphthalene ratios, together with an evaluation of their removal rates, indicate that the gas-phase nitration of naphthalene is more likely to be initiated by •NO3 + •NO2 (yielding 1NN:2NN ≈ 2.5:1) than by •OH + •NO2 (yielding 1NN:2NN ≈ 1:1). Nitronaphthalenes, less volatile than the parent compound, can then be found in particulate matter. In contrast, the occurrence of 9-nitroanthracene could be consistent with an electrophilic, condensed-phase nitration process.