Study of the Uptake of N2O5 by Water and NaCl Solutions

Abstract

The uptake of N2O5 by pure water and NaCl solution was studied as a function of temperature in the range from 262 to 278 K with the droplet train technique, where a highly controlled beam of droplets was exposed to N2O5 in a low-pressure flow tube reactor, and the formation of nitrate in the liquid phase was determined by ion chromatography. The uptake coefficients, y, for N2O5 on pure water are observed to decrease from 0.03 to 0.0 13 with increasing temperature. This behavior corresponds to the expected negative temperature dependence of mass accommodation leading to an enthalpy m o b , = (-9.6 f 1.6) kcal mol-' and to an entropy m o b s = (-43 f 6) cal mol-' K-l for the phase transfer, corresponding to a continuous nucleation process with a critical cluster size N* of about 2.4. A significantly lower yield of nitrate than with pure water is observed in the experiments on NaCl solution (1 mol/L), indicating that nitrogen compounds (such as ClN02) are formed after the uptake of N2O5 by subsequent reactions with NaCl and escape from the droplets. After correction for the known yield for the formation of CIN02, the results exhibit a slight systematic tendency for the uptake coefficient on NaCl solution to be greater than on pure water, indicating that the uptake of N2O5 by these aqueous media might be reaction-controlled. This assumption leads to a lower limit of 800 mol L-I atm-I s-l12 for the product Hk112 from a simple steady state model (where H is the Henry's law constant for N2O5 and k is the first-order hydrolysis rate constant).

Reactive uptake coefficients for heterogeneous reaction of N<sub>2</sub>O<sub>5</sub> with submicron aerosols of NaCl and natural sea salt

“…The protonated nitric acid intermediate, formed in a pseudo first order dissociative reaction involving water molecules, replaces the NO + 2 ion in earlier proposed mechanisms (George et al, 1994;Behnke et al, 1997;Schweitzer et al, 1998;Hallquist et al, 2003;Sohn et al, 1999).…”

“…The "thick film" uptake coefficient can be compared with uptake coefficients measured on larger droplets and bulk liquid films (George, 1994;Behnke, 1997;Schweitzer, 1998). Calculation of γ thick , requires determination of k r in order to calculate the reacto-diffusive length, l, and hence q.…”

“…George et al (1994) and Schweitzer et al (1998) have investigated N 2 O 5 uptake on a fast droplet train (80-150 µm diameter particles) equipped with FTIR/long-path absorption and ion-trap mass spectrometry for gas phase detection of N 2 O 5 (concentration = 20-2000 ppm) and products. The recommended mean uptake coefficient was γ =0.018±0.003, which was independent of temperature in the range 263-278 K, as well as of the NaCl concentration up to 1 M. The earlier droplet train experiments (George et al, 1994), in which the extent of reaction was followed by measuring the NO − 3 concentration in the collected droplets, gave similar values of γ .…”

Estimating N<sub>2</sub>O<sub>5</sub> uptake coefficients using ambient measurements of NO<sub>3</sub>, N<sub>2</sub>O<sub>5</sub>, ClNO<sub>2</sub> and particle-phase nitrate

“…In the presence of chloride, ClNO 2 can also be formed (Finlayson-Pitts et al, 1989;George et al, 1994;Behnke et al, 1997).…”

Knudsen cell studies of the reactions of N2O5 and ClONO2 with NaCl: development and application of a model for estimating available surface areas and corrected uptake coefficients

“…This hydrolysis is believed to occur through the autoionization of N 2 O 5 in solution and/or at the aqueous surface, followed by the reaction of NO 2 + with water to produce HNO 3 . However, if chloride ions are present, there is a competition between the reactions of NO 2 + with water and Cl À , and ClNO 2 is generated: 3,5,8,[10][11][12][13][14][15][16] …”