Modeling the Formation, Degradation, and Spatiotemporal Distribution of 2-Nitrofluoranthene and 2-Nitropyrene in the Global Atmosphere.

Polycyclic aromatic hydrocarbons (PAHs) are common atmospheric pollutants and known to cause adverse health effects. Nitrated PAHs (NPAHs) are formed in combustion activities and by nitration of PAHs in the atmosphere and may be equally or more toxic, but their spatial and temporal distribution in the atmosphere is not well characterized. Using the global EMAC model with atmospheric chemistry and surface compartments coupled, we investigate the formation, abundance, and fate of two secondarily formed NPAHs, 2-nitrofluoranthene (2-NFLT) and 2-nitropyrene (2-NPYR). The default reactivity scenario, the model with the simplest interpretation of parameters from the literature, tends to overestimate both absolute concentrations and NPAH/PAH ratios at observational sites. Sensitivity scenarios indicate that NO2-dependent NPAH formation leads to better agreement between measured and predicted NPAH concentrations and that photodegradation is the most important loss process of 2-NFLT and 2-NPYR. The highest concentrations of 2-NFLT and 2-NPYR are found in regions with strong PAH emissions, but because of continued secondary formation from the PAH precursors, these two NPAHs are predicted to be spread across the globe.

Atmospheric transport of persistent organic pollutants to and from the Arctic under present-day and future climate.

The long-term atmospheric cycling and fate of persistent organic pollutants under the influence of a changing climate is a concern. A GCM's realization of present-day (1970-1999) and future (2070-2099) climate, the latter under a medium scenario of greenhouse gas emissions, is used to study meridional transports and their correlations with the Arctic and North Atlantic Oscillations (AO and NAO). Regions of import and export maxima into the Arctic are identified along the Arctic Circle. It is found that, under future climate conditions, the net export of PCB153 out of the Arctic will increase. The meridional net flux pattern of this substance is expected to become independent of AO and NAO. For DDT, a trend of decreasing net Arctic import will reverse to an increasing trend 100 years after peak emission, which is partly due to more frequent AO and NAO positive phases. It is concluded that the long-term accumulation trends in the Arctic of other persistent pollutants, including so-called emerging pollutants, are subject to the substances' specific behavior and fate in the environment and need to be studied specifically.

Temperature effect on phase state and reactivity controls atmospheric multiphase chemistry and transport of PAHs.

Polycyclic aromatic hydrocarbons like benzo(a)pyrene (BaP) in atmospheric particulate matter pose a threat to human health because of their high carcinogenicity. In the atmosphere, BaP is mainly degraded through a multiphase reaction with ozone, but the fate and atmospheric transport of BaP are poorly characterized. Earlier modeling studies used reaction rate coefficients determined in laboratory experiments at room temperature, which may overestimate/underestimate degradation rates when applied under atmospheric conditions. Moreover, the effects of diffusion on the particle bulk are not well constrained, leading to large discrepancies between model results and observations. We show how regional and global distributions and transport of BaP can be explained by a new kinetic scheme that provides a realistic description of the temperature and humidity dependence of phase state, diffusivity, and reactivity of BaP-containing particles. Low temperature and humidity can substantially increase the lifetime of BaP and enhance its atmospheric dispersion through both the planetary boundary layer and the free troposphere. The new scheme greatly improves the performance of multiscale models, leading to better agreement with observed BaP concentrations in both source regions and remote regions (Arctic), which cannot be achieved by less-elaborate degradation schemes (deviations by multiple orders of magnitude). Our results highlight the importance of considering temperature and humidity effects on both the phase state of aerosol particles and the chemical reactivity of particulate air pollutants.