Abstract
Abstract. Aerosol simulations in chemistry transport models (CTMs) still suffer from numerous uncertainties, and diagnostic evaluations are required to point out major error sources. This paper presents an original approach to evaluate CTMs based on local and imported contributions in a large megacity rather than urban background concentrations. The study is applied to the CHIMERE model in the Paris region (France) and considers the fine particulate matter (PM2.5) and its main chemical constituents (elemental and organic carbon, nitrate, sulfate and ammonium), for which daily measurements are available during a whole year at various stations (PARTICULES project). Back-trajectory data are used to locate the upwind station, from which the concentration is identified as the import, the local production being deduced from the urban concentration by subtraction. Uncertainties on these contributions are quantified. Small biases in urban background PM2.5 simulations (bias of +16%) hide significant error compensations between local and advected contributions, as well as in PM2.5 chemical compounds. In particular, winter time organic matter (OM) imports appear strongly underestimated while local OM and elemental carbon (EC) production is overestimated all along the year. Erroneous continental wood burning emissions and missing secondary organic aerosol (SOA) pathways may explain errors on advected OM, while the carbonaceous compounds is likely to be related to errors in emissions and dynamics. A statistically significant local formation of nitrate is also highlighted from observations, but missed by the model. Together with the overestimation of nitrate imports, it leads to a bias of +51% on the local PM2.5 contribution. Such an evaluation finally gives more detailed insights on major gaps in current CTMs on which future efforts are needed.
Highlights
Fine particulate matter (PM2.5, particulate matter with aerodynamic diameter below 2.5 μm) pollution is well-known to produce adverse health effects (Chow et al, 2006), and to affect ecosystems and monuments through acidic deposition soiling (Likens et al, 1996; Lombardo et al, 2013)
Due to the complexity of wind fields, this procedure is certainly too simplistic to account for all meteorological situations that may occur over the Paris region
A quick overview of observed pollution regimes during the whole year is presented in a second part, with annual average results from observations (Sect. 5.2)
Summary
Fine particulate matter (PM2.5, particulate matter with aerodynamic diameter below 2.5 μm) pollution is well-known to produce adverse health effects (Chow et al, 2006), and to affect ecosystems and monuments through acidic deposition soiling (Likens et al, 1996; Lombardo et al, 2013). It impacts on climate directly through its diffusing and absorptive properties and indirectly through various modifications of cloud properties (Lohmann and Feichter, 2005), leading to changes in the earth radiative balance (Forster et al, 2007). Trends in PM2.5 concentrations remain unclear (EEA, 2012), due to variations in meteorological conditions and due to the possibly important contribution of biogenic sources
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