title: Relationship between different size classes of particulate matter and meteorology in three European cities.
abstract: Evidence on the correlation between particle mass and (ultrafine) particle number concentrations is limited. Winter- and spring-time measurements of urban background air pollution were performed in Amsterdam (The Netherlands), Erfurt (Germany) and Helsinki (Finland), within the framework of the EU funded ULTRA study. Daily average concentrations of ambient particulate matter with a 50% cut off of 2.5 microm (PM2.5), total particle number concentrations and particle number concentrations in different size classes were collected at fixed monitoring sites. The aim of this paper is to assess differences in particle concentrations in several size classes across cities, the correlation between different particle fractions and to assess the differential impact of meteorological factors on their concentrations. The medians of ultrafine particle number concentrations were similar across the three cities (range 15.1 x 10(3)-18.3 x 10(3) counts cm(-3)). Within the ultrafine particle fraction, the sub fraction (10-30 nm) made a higher contribution to particle number concentrations in Erfurt than in Helsinki and Amsterdam. Larger differences across the cities were found for PM2.5(range 11-17 microg m(-3)). PM2.5 and ultrafine particle concentrations were weakly (Amsterdam, Helsinki) to moderately (Erfurt) correlated. The inconsistent correlation for PM2.5 and ultrafine particle concentrations between the three cities was partly explained by the larger impact of more local sources from the city on ultrafine particle concentrations than on PM2.5, suggesting that the upwind or downwind location of the measuring site in regard to potential particle sources has to be considered. Also, relationship with wind direction and meteorological data differed, suggesting that particle number and particle mass are two separate indicators of airborne particulate matter. Both decreased with increasing wind speed, but ultrafine particle number counts consistently decreased with increasing relative humidity, whereas PM2.5 increased with increasing barometric pressure. Within the ultrafine particle mode, nucleation mode (10-30 nm) and Aitken mode (30-100 nm) had distinctly different relationships with accumulation mode particles and weather conditions. Since the composition of these particle fractions also differs, it is of interest to test in future epidemiological studies whether they have different health effects.
authors.affiliation: Utrecht University, Institute for Risk Assessment Sciences, Environmental and Occupational Health division, Jenalaan 18a, 3584 CK Utrecht, The Netherlands. j.dehartog@iras.uu.nl
authors.forename: Jeroen J
authors.initials: JJ
authors.lastname: de Hartog
authors.forename: Gerard
authors.initials: G
authors.lastname: Hoek
authors.forename: Aadu
authors.initials: A
authors.lastname: Mirme
authors.forename: Thomas
authors.initials: T
authors.lastname: Tuch
authors.forename: Gerard P A
authors.initials: GP
authors.lastname: Kos
authors.forename: Harry M
authors.initials: HM
authors.lastname: ten Brink
authors.forename: Bert
authors.initials: B
authors.lastname: Brunekreef
authors.forename: Josef
authors.initials: J
authors.lastname: Cyrys
authors.forename: Joachim
authors.initials: J
authors.lastname: Heinrich
authors.forename: Mike
authors.initials: M
authors.lastname: Pitz
authors.forename: Timo
authors.initials: T
authors.lastname: Lanki
authors.forename: Marko
authors.initials: M
authors.lastname: Vallius
authors.forename: Juha
authors.initials: J
authors.lastname: Pekkanen
authors.forename: Wolfgang G
authors.initials: WG
authors.lastname: Kreyling
mesh_terms: D000393:Air Pollutants / Q000032:analysis* / Q000737:chemistry; D002947:Cities; D004781:Environmental Exposure; D004784:Environmental Monitoring / Q000379:methods*; D005060:Europe; D006801:Humans; D006813:Humidity; D008685:Meteorological Concepts; D010316:Particle Size; D012044:Regression Analysis; D012621:Seasons; D013696:Temperature; D014504:Urban Health; D014919:Wind
chemical_list: D000393:Air Pollutants