Abstract
Abstract. A correct description of fine (diameter <1 μm) and ultrafine (<0.1 μm) aerosol particles in urban areas is of interest for particle exposure assessment but also basic atmospheric research. We examined the spatio-temporal variability of atmospheric aerosol particles (size range 3–800 nm) using concurrent number size distribution measurements at a maximum of eight observation sites in and around Leipzig, a city in Central Europe. Two main experiments were conducted with different time span and number of observation sites (2 years at 3 sites; 1 month at 8 sites). A general observation was that the particle number size distribution varied in time and space in a complex fashion as a result of interaction between local and far-range sources, and the meteorological conditions. To identify statistically independent factors in the urban aerosol, different runs of principal component (PC) analysis were conducted encompassing aerosol, gas phase, and meteorological parameters from the multiple sites. Several of the resulting PCs, outstanding with respect to their temporal persistence and spatial coverage, could be associated with aerosol particle modes: a first accumulation mode ("droplet mode", 300–800 nm), considered to be the result of liquid phase processes and far-range transport; a second accumulation mode (centered around diameters 90–250 nm), considered to result from primary emissions as well as aging through condensation and coagulation; an Aitken mode (30–200 nm) linked to urban traffic emissions in addition to an urban and a rural Aitken mode; a nucleation mode (5–20 nm) linked to urban traffic emissions; nucleation modes (3–20 nm) linked to photochemically induced particle formation; an aged nucleation mode (10–50 nm). Additional PCs represented only local sources at a single site, or infrequent phenomena. In summary, the analysis of size distributions of high time and size resolution yielded a surprising wealth of statistical aerosol components occurring in the urban atmosphere over one single city. A paradigm on the behaviour of sub-μm urban aerosol particles is proposed, with recommendations how to efficiently monitor individual sub-fractions across an entire city.
Highlights
Atmospheric aerosol particles have been acknowledged to play a key role with respect to the global balance of climate (Haywood and Boucher, 2000; Stott et al, 2000; Ramanathan et al, 2001)
We examined the spatio-temporal variability of atmospheric aerosol particles using concurrent number size distribution measurements at a maximum of eight observation sites in and around Leipzig, a city in Central Europe
In the previous Section we showed the existence of largescale components of the particle number size distribution (PNSD)
Summary
Atmospheric aerosol particles have been acknowledged to play a key role with respect to the global balance of climate (Haywood and Boucher, 2000; Stott et al, 2000; Ramanathan et al, 2001). Understanding the properties and the lifecycle of the entire particle size distribution is required to assess aerosol-driven climate effects. Aerosol particles have been recognised as a potential adverse factor for human health (Pope et al, 2002; WHO, 2002; Oberdoster, 2005). While many of the health-related evidence has been based on PM10 mass concentrations as a particle metric, specific questions have arisen which particular aerosol types might be responsible, and how the exposure risk for the population may be reduced in a cost-efficient way. Acqueous phase chemi- Max in aerodynamic mass distribucal reactions tion. Droplet mode from cloud processing Aerodynamic diameter. Activation of condensa- Aerodynamic diameter tion mode, cloud-fog drops, aqueous phase chemistry. >300, 240– Sea spray or droplet mode. Large-mode organics, total inorganics Mode of mass size distribution Droplet AcM. Hidy (1975) Hering and Friedlander (1982) John et al (1990) Meng and Seinfield (1994)
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