Heterogeneous Reactions of Particulate Matter-Bound PAHs and NPAHs with NO₃/N₂O₅, OH Radicals, and O₃ under Simulated Long-Range Atmospheric Transport Conditions: Reactivity and Mutagenicity

Abstract

The heterogeneous reactions of ambient particulate matter (PM)-bound polycyclic aromatic hydrocarbons (PAHs) and nitro-PAHs (NPAHs) with NO3/N2O5, OH radicals, and O3 were studied in a laboratory photochemical chamber. Ambient PM2.5 and PM10 samples were collected from Beijing, China and Riverside, California, and exposed under simulated atmospheric long-range transport conditions for O3 and OH and NO3 radicals. Changes in the masses of 23 PAHs and 20 NPAHs, as well as the direct and indirect-acting mutagenicity of the PM (determined using the Salmonella mutagenicity assay with TA98 strain), were measured prior to and after exposure to NO3/N2O5, OH radicals, and O3. In general, O3 exposure resulted in the highest relative degradation of PM-bound PAHs with more than four rings (benzo[a]pyrene was degraded equally well by O3 and NO3/N2O5). However, NPAHs were most effectively formed during the Beijing PM exposure to NO3/N2O5. In ambient air 2-nitrofluoranthene (2-NF) is formed from gas-phase NO3 radical- and OH radical-initiated reactions of fluoranthene, and 2-nitropyrene (2-NP) is formed from gas-phase OH radical-initiated reaction of pyrene. There was no formation of 2-NF or 2-NP in any of the heterogeneous exposures, suggesting that gas-phase formation of NPAHs did not play an important role during chamber exposures. Exposure of Beijing PM to NO3/N2O5 resulted in an increase in direct-acting mutagenic activity which was associated with the formation of mutagenic NPAHs. No NPAH formation was observed in any of the exposures of the Riverside PM. This was likely due to the accumulation of atmospheric degradation products from gas-phase reactions of volatile species onto the surface of PM collected in Riverside prior to exposure in the chamber, thus decreasing the availability of PAHs for reaction.

Global long-range transport and lung cancer risk from polycyclic aromatic hydrocarbons shielded by coatings of organic aerosol

“…completely (18). Other measurements have demonstrated that heterogeneous oxidation of particle-surface-bound PAHs in the atmosphere decreases substantially due to accumulation of SOA species over particles during their atmospheric transport and chemical aging (23). Heterogeneous reactions of PAHs with ozone are limited mostly to the particle surface, where ozone can be catalytically destroyed (24).…”

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

“…Although it has been shown that O 3 was an effective oxidant for heterogeneous reactions of particle-bound PACs (Jariyasopit et al, 2014), it should also be noted that in a real world environment the coexistence of O 3 and other atmospheric oxidants (e.g. OH radicals, NO 3 radicals, NO 2 , N 2 O 5 ) could complicate the degradation reactions of the PACs associated with PUF disks.…”

“…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.…”

“…also likely that in ambient air, the fraction of the reactive PACs on freshly emitted particles that are available for chemical reactions would have already partially reacted in the atmosphere prior to collection. (Jariyasopit et al, 2014) These particle-bound PACs will become less available for further degradation as particles are photochemically aged. Additionally, as shown in previous studies (Pitts et al, 1986;P€ oschl et al, 2001) and this study, humidity can potentially promote the stability of the PACs by suppressing O 3 reactions.…”

“…There are several studies investigating heterogeneous reactions of surface-bound PAHs with gaseous oxidants using various substrates including silica, graphite, soot particles, particulate matter, and glass fiber filters. (Bedjanian and Nguyen, 2010;Esteve et al, 2004;Jariyasopit et al, 2014;Nguyen et al, 2009;Perraudin et al, 2007;P€ oschl et al, 2001;Ringuet et al, 2012) The results from previous studies suggest that O 3 was an effective oxidant for degrading surface-bound PAHs (Jariyasopit et al, 2014;Pitts et al, 1986). As a result, for passive sampling methods where PUFs are protected from direct sunlight, wet precipitation, and strong wind inside sampler housings, it is likely that heterogeneous reactions with O 3 will play an important role in degrading PACs associated with PUFs.…”