THE SPATIAL AND TEMPORAL VARIATION OF MEASURED URBAN PM_(10) AND PM_(2.5) IN THE HELSINKI METROPOLITAN AREA

摘要

We have studied particulate matter (PM) concentrations, PM_(10) and PM_(2.5), measured in an urban air quality monitoring network in the Helsinki Metropolitan Area during 1997―1999. The data includes PM_(10) concentrations measured at five locations (two urban traffic, one suburban traffic, one urban background and one regional background site) and PM_(2.5) concentrations measured at two locations (urban traffic and urban background sites). The concentrations of PM_(10) show a clear diurnal variation, as well as a spatial variation within the area. By contrast, both the spatial and temporal variation of the PM_(2.5) concentrations was moderate. We have analysed the evolution of urban PM concentrations in terms of the relevant meteorological parameters in the course of one selected peak pollution episode during 21―31 March, 1998. The meteorological variables considered included wind speed and direction, ambient temperature, precipitation, relative humidity, atmospheric pressure at the ground level, atmospheric stability and mixing height. The elevated PM concentrations during the 1998 March episode were clearly related to conditions of high atmospheric pressure, relatively low ambient temperatures and low wind speeds in predominantly stable atmospheric conditions. The results provide indirect evidence indicating that the PM_(10) concentrations originate mainly from local vehicular traffic (direct emissions and resuspension), while the PM_(2.5) concentrations are mostly of regionally and long-range transported origin.