PAC concentrations from urban filter samples
J. Lintelmann (HMGU), G. Matuschek (HMGU)
Airborne particulate matter (PM) is an important pollutant in urban atmospheres and it has become of great concern in relation to public health because epidemiological studies have shown that exposure to particles with aerodynamic diameters < 10 µm (PM10) and especially < 2.5 µm (PM2.5) induces an increase of morbidity and mortality.
Nowadays regulatory standards have been promulgated for PM10 and PM2.5 concentrations in air but there is still a fundamental lack of understanding the underlying mechanisms of their toxicity. One widely accepted hypothesis is that particle toxicity not only depends on their physical properties but also on their composition. Chemical components of suspended particulate matter are very diverse. They range from highly water soluble salts through insoluble sooty particles made up mainly of elemental carbon coated by organic compounds to water insoluble minerals such as clay particles. Furthermore, additional airborne chemical and biological substances can interact with and adsorb on the particles during transport, deposition and collection. Studies performed on diesel exhaust particles (DEP) as well as on concentrated air particulates and organic extracts of DEP led to the conclusion that organic compounds adsorbed on particulate matter probably play an important role in generation of adverse health effects.
One main class of this organic part is represented by polycyclic aromatic compounds (PAC) which may trigger a large diversity of impairments ranging from acute inflammation processes to chronic diseases like cancer.
For the investigation of sources, behaviour, fate and effects of these substances as well as for the installation and successful application of monitoring networks reliable analytical methods for the routine determination of PAC are fundamental tools.
For this purpose four different liquid chromatography (LC) based methods were developed, validated and routinely applied for the analysis of polycyclic aromatic hydrocarbons (PAH), nitro-PAH, PAH-diones, and azaarenes on particulate matter.
During 2005 and 2006/2007 PM2.5 was collected on quartz fiber filters with a high volume sampler (HVS) operated for 24 h every third day. In 2005 the HVS was installed at the Munich city border close to a two-lane arterial road and one of its crossroads. In 2006/2007 the sampling site was in the city centre in the neighborhood of a main road and several back roads. In 2005, some meteorological data like radiation and temperature were acquired, in 2006 additional information like concentration of NOx, PM10, PM2.5 and ozone was collected.
Applying LC methods coupled with fluorescence and tandem mass spectrometry, relevant PAH (13 target analytes), nitro-PAH (3 substances) and PAH-diones (5 compounds) were determined after extraction and clean-up of the extracts.
PAH-concentrations at the suburban sampling site in 2005 were generally higher than those in the city centre in 2006/2007, but all concentration levels were similar to those observed in previous studies. For both locations significant temperature correlations of ΣPAH were found (r > 0.47). Correlation with ozone, NO, NOx was assessed for data in 2006/2007 (r > 0.46 ). The results emphasize the dependence of PAH concentrations on meteorological conditions determining degradation and derivatization processes, atmospheric dispersion, gas/particle partition and of course amount of emission (e.g. domestic heating, cold starts, increased traffic).
- Monthly mean PAH concentrations on PM2.5 and ambient temperature in 2005 and 2006/2007.
Both locations seem to be dominated by traffic emission. This assumption is supported by significant levels of benzo[ghi]perylene and coronene, which are typical markers for motor vehicles. A further hint for traffic dominance is the presence of 1-nitropyrene in all samples at both locations. 1-Nitropyrene is considered to be a valuable marker for diesel exhaust. 2-Nitrofluoranthene (2-NF) and 2-nitropyrene (2-NP) are formed via gas-phase reactions with OH or NO3 radicals (only 2-NF) in the presence of NO2. A 2-NF/2-NP ratio close to ten connotes daytime OH-initiated reactions, ratios > 100 indicate the dominance of nighttime, NO3-initiated formation. In both sampling periods daytime OH-initiated generation of nitro-PAH clearly dominated.
- Monthly mean values for concentrations of: 1-nitropyrene 05 (black column), 1-nitropyrene 06 (dark blue), 2-nitropyrene 05 (dark grey), 2-nitropyrene 06 (blue), 2-nitrofluoranthene 05 (grey), 2-nitrofluoranthene 06 (light blue) and for ratios: 2-NF/1-NP 05 (red line), 2-NF/1-NP 06 (green line), 2-NF/2-NP 05 (orange line), 2-NF/2-NP 06 (yellow line).
Three compounds, benzo[a]pyrenediones, phenanthrene-9,10-dione and chrysene-5,6-dione were quantified. Oxy-PAH are of toxicological interest due to their ability to generate reactive oxygen species in cell systems. They are generated during incomplete combustion processes and during atmospheric transport via oxidation of PAH. Similar sources and the generation mechanism explain the high correlation with parent PAH (r > 0.6). Contrary to nitro-PAH the correlation with temperature is high and it can be expected that concentration levels of oxy-PAH investigated depend on meteorological conditions in a manner comparable to PAH.
Actually, further multivariate statistics are applied for a more detailed source apportionment of the substances analyzed.
