Abstract
Abstract. Simulations with the chemistry transport model CHIMERE are compared to measurements performed during the MEGAPOLI (Megacities: Emissions, urban, regional and Global Atmospheric POLlution and climate effects, and Integrated tools for assessment and mitigation) summer campaign in the Greater Paris region in July 2009. The volatility-basis-set approach (VBS) is implemented into this model, taking into account the volatility of primary organic aerosol (POA) and the chemical aging of semi-volatile organic species. Organic aerosol is the main focus and is simulated with three different configurations with a modified treatment of POA volatility and modified secondary organic aerosol (SOA) formation schemes. In addition, two types of emission inventories are used as model input in order to test the uncertainty related to the emissions. Predictions of basic meteorological parameters and primary and secondary pollutant concentrations are evaluated, and four pollution regimes are defined according to the air mass origin. Primary pollutants are generally overestimated, while ozone is consistent with observations. Sulfate is generally overestimated, while ammonium and nitrate levels are well simulated with the refined emission data set. As expected, the simulation with non-volatile POA and a single-step SOA formation mechanism largely overestimates POA and underestimates SOA. Simulation of organic aerosol with the VBS approach taking into account the aging of semi-volatile organic compounds (SVOC) shows the best correlation with measurements. High-concentration events observed mostly after long-range transport are well reproduced by the model. Depending on the emission inventory used, simulated POA levels are either reasonable or underestimated, while SOA levels tend to be overestimated. Several uncertainties related to the VBS scheme (POA volatility, SOA yields, the aging parameterization), to emission input data, and to simulated OH levels can be responsible for this behavior. Despite these uncertainties, the implementation of the VBS scheme into the CHIMERE model allowed for much more realistic organic aerosol simulations for Paris during summertime. The advection of SOA from outside Paris is mostly responsible for the highest OA concentration levels. During advection of polluted air masses from northeast (Benelux and Central Europe), simulations indicate high levels of both anthropogenic and biogenic SOA fractions, while biogenic SOA dominates during periods with advection from Southern France and Spain.
Highlights
Human activities in large urban agglomerations cause large amounts of pollutant emissions, with negative effects on air quality and human health at the local and regional scale (Gurjar et al, 2008; Sicard et al, 2011)
The modeled secondary inorganic salt concentrations from both volatility-basis-set approach (VBS)-T2 and VBS-MEGAPOLI project emission inventory (MPOLI) simulations are generally overestimated with respect to the aerosol mass spectrometer (AMS) measuremasses which affects the formation of secondary organic aerosol
Modeled primary organic aerosol (POA) and secondary organic aerosol (SOA) from all four simulations are compared to a 3-factor positive matrix factorization (PMF) analysis (Freutel et al, 2013) on OA measured by AMS at LHVP (Table 3)
Summary
Human activities in large urban agglomerations cause large amounts of pollutant emissions, with negative effects on air quality and human health at the local and regional scale (Gurjar et al, 2008; Sicard et al, 2011). Simulations using the VBS approach in which evaporation of POA emissions, additional IVOC emissions, and chemical aging of gas phase IVOC and SVOC were taken into account gave better agreement in terms of SOA mass when compared to measurement than simulations using traditional SOA formation schemes. These studies suggest that OPOA produced from oxidation of gas phase IVOC and SVOC might represent a non-negligible fraction of SOA.
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