TY - JOUR
T1 - Interaction of ozone and water vapor with spark discharge soot aerosol particles coated with benzo[a]pyrene
T2 - O3 and H2O adsorption, benzo[a]pyrene degradation, and atmospheric implications
AU - Pöschl, Ulrich
AU - Letzel, Thomas
AU - Schauer, Christian
AU - Niessner, Reinhard
PY - 2001/4/26
Y1 - 2001/4/26
N2 - 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 O3 and H2O on the particles followed by a slower surface reaction between adsorbed O3 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 O3 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 H2O 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: O3 and H2O Langmuir adsorption equilibrium constants Ko3 = (2.8 ± 0.2) × 10-13 cm3 and KH2O = (2.1 ± 0.4) × 10-17 cm3, maximum pseudo-first-order BaP decay rate coefficient k1,4 = (0.015 ± 0.001) s-1, adsorption site surface concentration [SS]s = (5.7 ± 1.7) × 1014 cm-2. On the basis of these values, a second-order BaP-O3 surface reaction rate coefficient k2,s = (2.6 ± 0.8) × 10-17 cm2 s-1 can be calculated, and estimates for the mean surface residence times and adsorption enthalpies of O3 and H2O have been derived: τo3 5-18 s; τH2o ≈ 3 ms, Δads,o3 ≈ -(80-90) kJ mol-1, ΔHads,H,o ≈ -50 kJ mol-1. The results and their atmospheric implications are discussed in view of related studies.
AB - 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 O3 and H2O on the particles followed by a slower surface reaction between adsorbed O3 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 O3 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 H2O 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: O3 and H2O Langmuir adsorption equilibrium constants Ko3 = (2.8 ± 0.2) × 10-13 cm3 and KH2O = (2.1 ± 0.4) × 10-17 cm3, maximum pseudo-first-order BaP decay rate coefficient k1,4 = (0.015 ± 0.001) s-1, adsorption site surface concentration [SS]s = (5.7 ± 1.7) × 1014 cm-2. On the basis of these values, a second-order BaP-O3 surface reaction rate coefficient k2,s = (2.6 ± 0.8) × 10-17 cm2 s-1 can be calculated, and estimates for the mean surface residence times and adsorption enthalpies of O3 and H2O have been derived: τo3 5-18 s; τH2o ≈ 3 ms, Δads,o3 ≈ -(80-90) kJ mol-1, ΔHads,H,o ≈ -50 kJ mol-1. The results and their atmospheric implications are discussed in view of related studies.
UR - http://www.scopus.com/inward/record.url?scp=0035953974&partnerID=8YFLogxK
U2 - 10.1021/jp004137n
DO - 10.1021/jp004137n
M3 - Article
AN - SCOPUS:0035953974
SN - 1089-5639
VL - 105
SP - 4029
EP - 4041
JO - Journal of Physical Chemistry A
JF - Journal of Physical Chemistry A
IS - 16
ER -