Abstract
Abstract. Carbon-containing particles have deleterious effects on both Earth's climate and human health. In Europe, the main sources of light-absorbing carbon (LAC) emissions are the transport (67%) and residential (25%) sectors. Information on the spatiotemporal variability of LAC particles in urban areas is relevant for air quality management and to better diagnose the population exposure to these particles. This study reports on results of an intensive field campaign conducted at four sites (two kerbside stations, one urban background site and a rural station) in Stockholm, Sweden, during the spring 2006. Light-absorbing carbon mass (MLAC) concentrations were measured with custom-built Particle Soot Absorption Photometers (PSAP). The spatiotemporal variability of MLAC concentrations was explored by examining correlation coefficients (R), coefficients of divergence (COD), and diurnal patterns at all sites. Simultaneous measurements of NOx, PM10, PM2.5, and meteorological variables were also carried out at the same locations to help characterize the LAC emission sources. Hourly mean (± standard deviation) MLAC concentrations ranged from 0.36±0.50 at the rural site to 5.39±3.60 μg m−3 at the street canyon site. Concentrations of LAC between urban sites were poorly correlated even for daily averages (R<0.70), combined with highly heterogeneously distributed concentrations (COD>0.30) even at spatial scales of few kilometers. This high variability is connected to the distribution of emission sources and processes contributing to the LAC fraction at these sites. At urban sites, MLAC tracked NOx levels and traffic density well and mean MLAC/PM2.5 ratios were larger (26–38%) than at the background sites (4–10%). The results suggest that vehicle exhaust emissions are the main responsible for the high MLAC concentrations found at the urban locations whereas long-range transport (LRT) episodes of combustion-derived particles can generate a strong increase of levels at background sites. To decrease pollution levels at kerbside and urban background locations in Stockholm, we recommend abatement strategies that target reductions of vehicle exhaust emissions, which are the main contributors to MLAC and NOx concentrations.
Highlights
Primary carbonaceous particles are mostly emitted by combustion processes and represent a large fraction of the submicron aerosol
The results suggest that vehicle exhaust emissions are the main responsible for the high MLAC concentrations found at the urban locations whereas long-range transport (LRT) episodes of combustion-derived particles can generate a strong increase of levels at background sites
Krecl et al (2007), when comparing Aethalometer and Particle Soot Absorption Photometers (PSAP)-ITM measurements in an area impacted by woodsmoke, showed that the custom-built PSAP was a reliable alternative for the commercial Aethalometer
Summary
Primary carbonaceous particles are mostly emitted by combustion processes (transport, residential sector, industry, and power generation) and represent a large fraction of the submicron aerosol. Urban areas are characterized by higher population density, larger number of pollutant emission sources, higher atmospheric pollutants concentrations, and a higher LAC content in the fine particle (PM2.5) fraction (Putaud et al, 2004). Simultaneous and continuous timeresolved LAC measurements are required in different parts of the city to (1) characterize the carbon-containing particle sources which can be used to streamline successful air quality control strategies to safeguard public health, (2) understand the particles fate and transport in the urban atmosphere, (3) study the spatiotemporal variability of LAC particles to better diagnose the population exposure to these particles, and (4) determine to what extent the limit values for PM2.5 and PM10 regulate the LAC concentrations, since LAC would be a good candidate substance to be regulated if both climate and health effects of emissions are to be considered. The urban and rural contributions to the atmospheric pollutants load are discussed
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