The interaction of ozone and water vapor with spark discharge soot particles coated with the five-ring polycyclic aromatic hydrocarbon benzo[a]pyrene (BaP) has been investigated in aerosol flow tube experiments at ambient temperature and pressure (296 K, 1 atm). The investigated range of ozone volume mixing ratio (VMR) and relative humidity (RH) was 0-1 ppm and 0-25%, respectively. The observed gas-phase ozone losses and pseudo-first-order BaP decay rate coefficients exhibited Langmuir-type dependencies on gas-phase ozone concentration and were reduced in the presence of water vapor, which indicates rapid, reversible and competitive adsorption of O 3 and H 2 O on the particles followed by a slower surface reaction between adsorbed O 3 and BaP. At low ozone VMR and RH, the half-life of surface BaP molecules was found to be shorter than previously reported (∼ 5 min at 30 ppb O 3 under dry conditions). At higher RH and for multilayer BaP surface coverage, however, a strong increase of BaP half-life was observed and can be attributed to competitive H 2 O adsorption and to surface/bulk shielding effects, respectively. From four independent sets of ozone loss and BaP decay measurement data the following parameters have been derived: O 3 and H 2 O Langmuir adsorption equilibrium constants K O 3 ) (2.8 ( 0.2) × 10 -13 cm 3 and K H 2 O ) (2.1 ( 0.4) × 10 -17 cm 3 , maximum pseudo-first-order BaP decay rate coefficient k 1,4 ) (0.015 ( 0.001) s -1 , adsorption site surface concentration [SS] S ) (5.7 ( 1.7) × 10 14 cm -2 . On the basis of these values, a second-order BaP-O 3 surface reaction rate coefficient k 2,s ) (2.6 ( 0.8) × 10 -17 cm 2 s -1 can be calculated, and estimates for the mean surface residence times and adsorption enthalpies of O 3 and H 2 O have been derived: τ O 3 ≈ 5-18 s; τ H 2 O ≈ 3 ms, ∆H ads,O 3 ≈ -(80-90) kJ mol -1 , ∆H ads,H 2 O ≈ -50 kJ mol -1 . The results and their atmospheric implications are discussed in view of related studies.
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).
Polycyclic aromatic hydrocarbons (PAH) and their nitrated derivatives (nitro-PAH) are environmental pollutants which pose a threat to human health even at low concentration levels. In this study, efficient analytical methods for the analysis of nitro-PAH and PAH (extraction, clean-up, chromatographic separation, and spectrometric detection) have been developed, characterized, and applied to aerosol samples. The separation and quantification of 12 nitro-PAH was carried out by reversed-phase high performance liquid chromatography (HPLC), on-line reduction, and fluorescence detection. The detection limits were in the range of 0.03-0.5 microg L(-1) (6-100 pg in the investigated sample aliquots), and the recovery rates from soot samples were 70-90%. Nitro-PAH and PAH concentrations have been determined for different types of soot and for urban, rural, and alpine fine air particulate matter (PM2.5). For the first time, trace amounts of nitro-PAH have been detected in a high-alpine clean air environment. The on-line reduction and fluorescence technique has been complemented by atmospheric pressure chemical ionization time-of-flight mass spectrometry (APCI-TOF-MS). The MS detection allowed the analysis of partially nitrated and oxygenated PAH in laboratory studies of the heterogeneous reaction of PAH on soot and glass fiber substrates with gaseous nitrogen oxides and ozone. It led to the tentative identification of a previously unknown nitrated derivative of the particularly toxic PAH benzo[ a]pyrene (BaP-nitroquinone), and provides the first experimental evidence that PAH-nitroquinones can be formed by reaction of PAH with atmospheric photooxidants.
Abstract. Detailed investigations of the chemical and microphysical properties of rural continental aerosols were performed during the HAZE2002 experiment, which was conducted in May 2002 at the Meteorological Observatory Hohenpeissenberg (DWD) in Southern Germany.Online measurements included: Size-resolved chemical composition of submicron particles; total particle number concentrations and size distributions over the diameter range of 3 nm to 9 µm; gas-phase concentration of monoterpenes, CO, O 3 , OH, and H 2 SO 4 . Filter sampling and offline analytical techniques were used to determine: Fine particle mass (PM2.5), organic, elemental and total carbon in PM2.5 (OC2.5, EC2.5, TC2.5), and selected organic compounds (dicarboxylic acids, polycyclic aromatic hydrocarbons, proteins).Overall, the non-refractory components of submicron particles detected by aerosol mass spectrometry (PM1, 6.6±5.4 µg m −3 , arithmetic mean and standard deviation) accounted for ∼62% of PM2.5 determined by filter gravimetry (10.6±4.7 µg m −3 ). The relative proportions of nonrefractory submicron particle components were: (23±39)% ammonium nitrate, (27±23)% ammonium sulfate, and (50±40)% organics (OM1). OM1 was closely correlated with PM1 (r 2 =0.9) indicating a near-constant ratio of nonrefractory organics and inorganics.Correspondence to: J. Schneider (schneider@mpch-mainz.mpg.de)The average ratio of OM1 to OC2.5 was 2.1±1.4, indicating a high proportion of heteroelements in the organic fraction of the sampled rural aerosol. This is consistent with the high ratio of oxygenated organic aerosol (OOA) over hydrocarbon-like organic aerosol (HOA) inferred from the AMS results (4:1), and also with the high abundance of proteins (∼3%) indicating a high proportion of primary biological material (∼30%) in PM2.5. This finding was confirmed by low abundance of PAHs (<1 ng m −3 ) and EC (<1 µg m −3 ) in PM2.5 and detection of several secondary organic aerosol compounds (dicarboxylic acids) and their precursors (monoterpenes).New particle formation was observed almost every day with particle number concentrations exceeding 10 4 cm −3 (nighttime background level 1000-2000 cm −3 ). Closer inspection of two major events indicated that the observed nucleation agrees with ternary H 2 SO 4 /H 2 O/NH 3 nucleation and that condensation of both organic and inorganic species contributed to particle growth.
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