Abstract
Abstract. Polycyclic aromatic hydrocarbons (PAHs) are hazardous pollutants, with increasing emissions in pace with economic development in East Asia, but their distribution and fate in the atmosphere are not yet well understood. We extended the regional atmospheric chemistry model WRF-Chem (Weather Research Forecast model with Chemistry module) to comprehensively study the atmospheric distribution and the fate of low-concentration, slowly degrading semivolatile compounds. The WRF-Chem-PAH model reflects the state-of-the-art understanding of current PAHs studies with several new or updated features. It was applied for PAHs covering a wide range of volatility and hydrophobicity, i.e. phenanthrene, chrysene and benzo[a]pyrene, in East Asia. Temporally highly resolved PAH concentrations and particulate mass fractions were evaluated against observations. The WRF-Chem-PAH model is able to reasonably well simulate the concentration levels and particulate mass fractions of PAHs near the sources and at a remote outflow region of East Asia, in high spatial and temporal resolutions. Sensitivity study shows that the heterogeneous reaction with ozone and the homogeneous reaction with the nitrate radical significantly influence the fate and distributions of PAHs. The methods to implement new species and to correct the transport problems can be applied to other newly implemented species in WRF-Chem.
Highlights
Polycyclic aromatic hydrocarbons (PAHs), released into the atmosphere as by product of all kinds of combustion processes, are harmful for human health via inhalation as well as ingestion pathways (WHO, 2003; Lv et al, 2016) and for ecosystems (Hylland, 2006)
Compared to the previous PAH modelling studies, this work is unique in four aspects: (1) it includes all relevant state-of-the-art processes of PAH into WRF-chemical transport model (Chem) which are important for its cycling in the atmospheric environment over land, (2) predicts and validates against observed gas- and particulate-phase PAH concentrations separately, (3) validates atmospheric concentrations and particulate mass fraction against diurnal variable PAH observations, and (4) explores the significance of PAH
All the new variables related to emissions and concentration fields of PAHs and those intermediate variables used in different chemical and physical processes, such as air–soil gas exchange, gas-phase/heterogeneous reactions, cloud scavenging, dry/wet deposition, advective transport and cumulus convection, are first defined in registry.chem and included in respective sub-modules/routines
Summary
Polycyclic aromatic hydrocarbons (PAHs), released into the atmosphere as by product of all kinds of combustion processes, are harmful for human health via inhalation as well as ingestion pathways (WHO, 2003; Lv et al, 2016) and for ecosystems (Hylland, 2006). High emissions of PAHs in Asia pose a hazard to the ecosystems and human health on an intercontinental or even global scale (Hung et al, 2005). Since its initial release in 2002, Weather Research Forecast model with Chemistry module (WRF-Chem) has been widely applied and verified for regional air quality (Zhang et al, 2010, 2013) and climate (Liao et al, 2014; Yahya et al, 2016) study with high temporal and spatial resolutions. Compared to the previous PAH modelling studies, this work is unique in four aspects: (1) it includes all relevant state-of-the-art processes of PAH into WRF-Chem which are important for its cycling in the atmospheric environment over land (i.e. new heterogeneous degradation scheme, several oxidants in homogeneous degradation processes, and revolatilisation from soil, among others), (2) predicts and validates against observed gas- and particulate-phase PAH concentrations separately, (3) validates atmospheric concentrations and particulate mass fraction against diurnal variable PAH observations, and (4) explores the significance of PAH heterogeneous reaction with ozone (O3) and gas-phase reaction with nitrate radical (NO3)
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