Local and regional components of aerosol in a heavily trafficked street canyon in central London derived from PMF and cluster analysis of single-particle ATOFMS spectra.

Positive matrix factorization (PMF) has been applied to single particle ATOFMS spectra collected on a six lane heavily trafficked road in central London (Marylebone Road), which well represents an urban street canyon. PMF analysis successfully extracted 11 factors from mass spectra of about 700,000 particles as a complement to information on particle types (from K-means cluster analysis). The factors were associated with specific sources and represent the contribution of different traffic related components (i.e., lubricating oils, fresh elemental carbon, organonitrogen and aromatic compounds), secondary aerosol locally produced (i.e., nitrate, oxidized organic aerosol and oxidized organonitrogen compounds), urban background together with regional transport (aged elemental carbon and ammonium) and fresh sea spray. An important result from this study is the evidence that rapid chemical processes occur in the street canyon with production of secondary particles from road traffic emissions. These locally generated particles, together with aging processes, dramatically affected aerosol composition producing internally mixed particles. These processes may become important with stagnant air conditions and in countries where gasoline vehicles are predominant and need to be considered when quantifying the impact of traffic emissions.This is the author accepted manuscript. The final version is available via ACS at http://pubs.acs.org/doi/abs/10.1021/es506249z

Interaction of NO₂ with TiO₂ surface under UV irradiation: measurements of the uptake coefficient

The interaction of NO₂ with TiO₂ solid films was studied under UV irradiation using a low pressure flow reactor (1–10 Torr) combined with a modulated molecular beam mass spectrometer for monitoring of the gaseous species involved. The NO₂ to TiO₂ reactive uptake coefficient was measured from the kinetics of NO₂ loss on TiO₂ coated Pyrex rods as a function of NO₂ concentration, irradiance intensity (<i>J</i>_NO₂ = 0.002–0.012 s⁻¹), relative humidity (RH = 0.06–69 %), temperature (<i>T</i> = 275–320 K) and partial pressure of oxygen (0.001–3 Torr). TiO₂ surface deactivation upon exposure to NO₂ was observed. The initial uptake coefficient of NO₂ on illuminated TiO₂ surface (with 90 ppb of NO₂ and <i>J</i>_NO₂&cong;0.006 s⁻¹) was found to be &gamma;₀ = (1.2±0.4) &times;10^&minus;4 (calculated using BET surface area) under dry conditions at <i>T</i> = 300 K. The steady state uptake, &gamma;, was several tens of times lower than the initial one, independent of relative humidity, and was found to decrease in the presence of molecular oxygen. In addition, it was shown that γ is not linearly dependent on the photon flux and seems to level off under atmospheric conditions. Finally, the following expression for γ was derived, γ = 2.3×10⁻³ exp(&minus;1910/<i>T</i>)/(1 + <i>P</i>^0.36) (where <i>P</i> is O₂ pressure in Torr), and recommended for atmospheric applications (for any RH, near 90 ppb of NO₂ and <i>J</i>_NO₂ = 0.006 s⁻¹)

Uptake of HO2 radicals on Arizona Test Dust

International audienc

Heterogeneous Interaction of H2O2 with Arizona Test Dust

International audienceThe heterogeneous interaction of H2O2 with solid films of Arizona Test Dust (ATD) was investigated under dark conditions and in presence of UV light using a low pressure flow tube reactor coupled with a quadrupole mass spectrometer. The uptake coefficients were measured as a function of the initial concentration of gaseous H2O2 ([H2O2]0 = (0.18 – 5.1) × 1012 molecules cm–3), irradiance intensity (JNO2 = 0.002 – 0.012 s–1), relative humidity (RH = 0.002 – 69%), and temperature (T = 268 – 320 K). The initial uptake coefficient was found to be independent of the concentration of H2O2 and UV irradiation intensity and to decrease with increasing RH and temperature according to the following expressions: γ0 = 4.8 × 10–4/(1+ RH0.66) at T = 275 K and γ0 = 3.2 × 10–4/(1 + 2.5 × 1010exp(−7360/T)) at RH = 0.35% (calculated using BET surface area, estimated conservative uncertainty of 30%). By contrast, the steady state uptake coefficient was found to be independent of temperature, to increase upon UV irradiation of the surface, and to be inversely (γSS ∼ [H2O2]−0.6) dependent on the concentration of H2O2. The RH independent steady state uptake coefficient was measured under dark and UV irradiation conditions: γSS(dark) = (0.95 ± 0.30) × 10–5 and γSS(UV) = (1.85 ± 0.55) × 10–5, for RH = (2 – 69)% and [H2O2]0 ≅ 1.0 × 1012 molecules cm–3. The present experimental data support current considerations that uptake of H2O2 on mineral aerosol is potentially an important atmospheric process