Evaluation of a modelling system for predicting the concentrations of PM_(2.5) in an urban area

摘要

We present a modelling system that contains a treatment of the emissions and atmospheric dispersion of fine particiulate matter (PM_(2.5)) on an urban scale, combined with a statistical model for estimating the contribution of long-range transported aerosols. The model of PM_(2.5) emissions includes exhaust emissions, cold starts and driving, as well as, non-exhaust emissions originated from urban vehicular traffic. The influence of primary vehicular emissions from the road and street network was evaluated using a roadside emission and dispersion model, CAR-FMI, in combination with a meteorological pre-processing model, MPP-FMI. We have computed hourly sequential time series of the PM_(2.5) concentrations in 2002 in a numerical grid in the Helsinki Metropolitan Area. The predicted results were compared against measured data at two locations in central Helsinki: urban roadside station of Vallila and urban background station of Kallio. The predicted daily average PM_(2.5) concentrations agreed well with the measured values; e.g., the index of agreement values were 0.83 and 0.86 at Vallila and Kallio, respectively, and the absolute values of fractional bias ≤ 0.13. As expected, the scatter of data points is substantially wider for the hourly concentration values; e.g., the index of agreement values were 0.69 and 0.74. We also computed the spatial concentration distributions of PM_(2.5). The predicted contribution from long-range transport to the street level PM_(2.5) varied spatially from 40% in the most trafficked areas to nearly 100% in the outskirts of the area. The emissions originated from cold starts and driving were responsible for < 4% of the annual average concentrations at the roadside and urban stations. The model can potentially be used as a practical tool of assessment of urban PM_(2.5) contributions in various European regions.