A European aerosol phenomenology – 3: Physical and chemical characteristics of particulate matter from 60 rural, urban, and kerbside sites across Europe
Introduction
Because aerosols affect human health, ecosystems (acidification, eutrophication) and visibility, emission abatement measures have been implemented over the last decades to reduce particle matter (PM10 and PM2.5) concentrations. As the legislation on particulate emission and air pollution is based on PM mass all over the world and is becoming more and more stringent (WHO, 2005), PM10 and PM2.5 concentrations are expected to further significantly decrease over the next decades. But can we assert that future PM concentration reductions will show positive effects on human health and ecosystems? Can we forecast the impact PM abatement measures on climate global and regional radiative forcing? Aerosol impacts are indeed linked to different characteristics that do not necessarily co-vary. Climate effects are related to its optical properties (scattering, absorption) throughout the atmospheric column, and cloud condensation formation potential, which in turn depends on particle size distribution and chemical composition. Impact on ecosystems depends on the deposition flux of specific species (acids, oxidized and reduced nitrogen, base cations, etc…). And we do not know yet which PM properties cause the health effects, although several epidemiological studies highlighted a link between short or long term exposure to PM mass concentration and human health (Zanobetti and Schwartz, 2005, Pope et al., 2008, Boldo et al., 2006, Pope, 2007, Miller et al., 2007). Therefore, abatement policies might be unnecessarily costly, inefficient, and even counter-productive if they address PM mass concentrations only. A thorough knowledge of the aerosol would help in designing a better legislation, using potential synergies and anticipating possible trade-offs between measures aiming at limiting air pollution and climate change. But PM10 and more recently also PM2.5 mass concentrations are still the only aerosol metrics measured systematically in national and international air pollution monitoring networks.
Our goal is to show how different (or similar) other aerosol characteristics can be among various sites located in different regions across Europe, even where equal PM mass concentrations are observed. These characteristics are generally not available from regulatory monitoring networks (see e.g. EMEP and AirBase data banks), but rather from research projects. We have already pursued this process in two previous works (Van Dingenen et al., 2004, Putaud et al., 2004). The present study revises our previous conclusions in the light of data collected from more than 30 new sites. In view of the current European directive on particulate air pollution (2008/50/EC), we stratified the data according to PM mass concentration bins to address the following questions: (1) can PM2.5 and PMcoarse mass concentrations be inferred from PM10 and PM2.5 mass concentrations, respectively, (2) which PM constituents are responsible for PM10 high mass concentrations, and (3) can sub-μm and ultrafine particle number concentrations be estimated based on PM2.5 mass concentration measurements. Answers are modulated according to the type of sites, from natural background to kerbside sites, and their location in Northwestern, Southern or Central Europe.
Section snippets
Compilation of European aerosol data
To achieve our goal, we selected data sets including PM mass concentrations on the one hand, and particle number and/or aerosol chemical composition data on the other hand, which were representative for a site during at least a season (i.e. minimum 6 weeks of continuous measurements). The selected sites and analytical methods employed are listed in Annexes 1 and 2.
Our previous articles (Van Dingenen et al., 2004, Putaud et al., 2004) were fruits of a voluntary collaboration among scientists for
PM10 and PM2.5 mass concentrations
While PM10 mass concentrations have been monitored by national and international air pollution monitoring networks for two decades (see e.g. EMEP and AirBase data banks), PM2.5 measurements are still being started up at many sites, because the new European Directive 2008/50/EC establishes target values for PM2.5 concentration and exposure to be met by 2010. Fig. 2a and b show 24-h averaged PM10 and PM2.5 yearly statistics observed at 48 sites across Europe (see also Annexes 3 and 4). The
Particle number concentrations
We collected aerosol particle data from 12 more sites compared to our previous work (Van Dingenen et al., 2004), mostly located in the Northwestern sector of Europe. Total (Dp > 10 nm) and ultrafine (10 < Dp < 100 nm) particle concentrations rather than detailed size distributions were generally available from these new sites. The size distributions measured with Scanning or Differential Mobility Sizing systems (S/DMPSs) were integrated from 10 nm upwards to obtain comparable data. The
Particulate matter chemical composition
Fig. 5a–c shows annual average chemical composition of PM10, PM2.5 (the fine fraction) and PMcoarse (= PM10 – PM2.5), respectively, at 39 sites, among which 23 are new compared to Putaud et al. (2004). Only sites for which at least one whole year of data was available are included in Fig. 5. A table with atmospheric concentrations of the main PM constituents is available in Annex 4.
Elemental carbon (EC), nitrate (NO3−), and ammonium (NH4+) concentrations derive directly from measurements.
Conclusions
Datasets on aerosol physical and chemical characteristics from more than 60 European sites were compiled, among which more than 30 were not part of our previous studies (Van Dingenen et al., 2004, Putaud et al., 2004). This work covers also the Mediterranean area, as well as Central Europe. It appears that regional differences in PM characteristics (particle number abundance, chemical composition) are significant enough to justify a grouping of sites in three large geographical sectors
Acknowledgements
This paper is a contribution to the COST Action 633 “Particulate matter: Properties related to health effects”.
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