Polycyclic Aromatic Hydrocarbons in Urban Air Particulate Matter:  Decadal and Seasonal Trends, Chemical Degradation, and Sampling Artifacts

Abstract

Aerosol filter samples collected at a major urban traffic junction (LKP) and at a suburban residential location (IWC) in the metropolitan area of Munich (Germany) throughout the years 2001 and 2002 have been analyzed for 12 of the 16 EPA priority polycyclic aromatic hydrocarbon (PAH) pollutants by liquid chromatography with fluorescence detection. The mean mass concentration of the sum of all investigated PAH in the sampled air at LKP (1.9-5.0 ng m(-3)) was roughly two times higher than at IWC (0.8-2.9 ng m(-3)), and at both locations it was about 2-3 times higher in winter (heating season) than in summer and spring or autumn. Comparisons with earlier measurement campaigns indicate a steep decrease of PAH abundance by almost an order of magnitude from 1980 to 1993 and a much slower decrease since then. Distinctly different seasonal trends and short-term fluctuations have been observed for semivolatile 3- and 4-ring PAH and for particle-bound 5- and 6-ring PAH. Based on systematic correlation analyses with a wide range of air quality parameters, most of the differences can be attributed to not only varying emissions but also chemical reactions with atmospheric oxidants which were found to play an important role. The results of denuder experiments prove that substantial degradation of the particularly toxic tracer benzo[a]pyrene and of the other investigated 5- and 6-ring PAH can occur during filter sampling and on airborne particles (formation of oxygenated and nitrated derivatives). Filter reaction artifacts are shown to lead to an underestimation of the actual PAH content of urban air particulate matter by up to 100% of the measurement value or more, with a near-linear dependence on ozone volume mixing ratio. The role and applicability of ozone as a tracer of atmospheric oxidizing capacity for particle-bound PAH is discussed and confirmed by comparison with earlier investigations and by complementary laboratory experiments (reaction kinetics and product studies).

Gas/particle partitioning and global distribution of polycyclic aromatic hydrocarbons – A modelling approach

“…The species and their degradation rates are listed in Table 1. Particle-associated PAHs rapidly react with ozone (Pöschl et al, 2001;Schauer et al, 2003;Tsapakis and Stephanou, 2003). On the other hand, observations in ambient air suggest that the reactivity of PAHs may be reduced when they are sorbed to aerosol particles (relative to their behaviour in the gas-phase), this is in contrast to the findings of laboratory studies.…”

Factors affecting atmospheric 1-, 2-nitropyrenes and 2-nitrofluoranthene in winter at Noto peninsula, a remote background site, Japan

“…Furthermore, Compared with Pyr and FR, BaP is the most reactive with all oxidants (Schauer et al, 2003;Tsapakis and Stephanou, 2003;Goriaux et al, 2006;Liu et al, 2006;Ringuet et al, 2012).…”

Raman Microspectroscopic Analysis of Size-Resolved Atmospheric Aerosol Particle Samples Collected with an ELPI: Soot, Humic-Like Substances, and Inorganic Compounds

“…Moreover, this study was focused on the identification and distinction of soot and humic-like substances, which are generally characterized by high thermochemical refractiveness and relatively low susceptibility for oxidation by gaseous reactants. Exposure of these substances to ozone and nitrogen oxides at ambient temperatures is likely to change their surface composition and content of organic trace substances but not their bulk composition and spectral parameters determined by Raman microspectroscopy (Pöschl et al 2001;Schauer et al 2003;Schauer et al 2004;Pöschl, 2005;Messerer et al 2006;Ivleva et al 2007). …”