Uptake of NO₃ on soot and pyrene surfaces

Abstract

[1] The reaction of NO 3 with methane soot, hexane soot, and solid pyrene was investigated using a flow tube reactor. The uptake of NO 3 on fresh soot was fast (uptake coefficient >0.1). Based on this result and an assumed density of reactive sites on soot, the time to process or oxidize 90% of a soot surface in the atmosphere would take only approximately five minutes. This suggests that NO 3 chemistry can rapidly oxidize soot surfaces under atmospheric conditions. After exposing soot films to NO 3 for approximately 180 minutes in the laboratory, the uptake reaches a steady-state value. The steady state uptake coefficients (assuming a geometric surface area) were 0.0054 ± 0.0027 and 0.0025 ± 0.0018 for methane and hexane soot, respectively. These numbers are used to show that heterogeneous reactions between NO 3 and soot are not likely a significant sink of gas-phase NO 3 under most atmospheric conditions. The uptake of NO 3 on fresh pyrene surfaces was also fast (uptake coefficient >0.1), and much faster than previously suggested. We argue that under certain atmospheric conditions reactions between NO 3 and surface-bound polycyclic aromatic hydrocarbons (PAHs) may be an important loss process of PAHs in the atmosphere.

Kinetic Studies of Heterogeneous Reactions of Polycyclic Aromatic Hydrocarbon Aerosols with NO3Radicals

“…According to eq 3, the uptake coefficients for NO 3 radicals on BaA, Ch, Py, 1-NP, and 1-OHP particles are 2.4, 1.5, 3.1, 0.5, and 4.8, respectively, which are much larger than the reported data. 12,27 Lambe et al 44 reported that evaporation followed by gas-phase oxidation was the main reason resulting in the uptake coefficients greater than unity observed in their experiment. In this experiment, the vapor pressures of the 4-ring PAHs are less than 6 × 10 −4 Pa and their gas-phase reaction rates with NO 3 radicals are on the order of 10 −17 − 10 −16 cm 3 ·molecule −1 ·s −1 .…”

An experimental technique for the direct measurement of N<sub>2</sub>O<sub>5</sub> reactivity on ambient particles

“…However, for γ (NO 3 )>0.1, our observations represent an upper limit for γ (N 2 O 5 ). While it is unlikely that γ (NO 3 ) is uniformly greater than 0.1, recent laboratory measurements suggest that γ (NO 3 ) could be large (γ (NO 3 )>0.1) on fresh soot (Gross and Bertram, 2008;Mak et al, 2007). By routinely shifting the N 2 O 5 -NO 3 ratio to higher NO 3 , via reducing NO 2 in the source, our approach can theoretically elucidate both N 2 O 5 and NO 3 reactivity on particles.…”

Effect of the blocked-sites phenomenon on the heterogeneous reaction of pyrene with N2O5/NO3/NO2

“…19 Although a mechanism has been recently suggested based on the gas-phase chemistry of PAHs with the NO 3 radical, specic markers for the radical-initiated isomer products (2-nitrouoranthene and 2-nitropyrene) were not observed during the heterogeneous chemical processes. 18,20,21 Ringuet et al reported the rst observation of the heterogeneous formation of 2-nitropyrene from particulate pyrene oxidation in the presence of O 3 /NO 2 , questioning its use as an indicator of NPAH formation in the gaseous phase. 22 Thus, the reaction mechanism of heterogeneous nitration has not been unequivocally identied.…”

“…18,19,21 To explore whether this problem of blocking reaction sites has a signicant impact on the heterogeneous reactions that occur on the PAH particle surface, we conducted an in-depth investigation of the heterogeneous oxidation of suspended pyrene (PY) …”