HONO decomposition on borosilicate glass surfaces: implications for environmental chamber studies and field experiments

Abstract

Nitrous acid (HONO) is the major source of OH in polluted urban atmospheres, so an understanding of its formation and loss processes both in urban atmospheres and in laboratory systems is important. Earlier studies over a limited range of conditions showed that HONO is taken up and undergoes reaction on surfaces. We report here a comprehensive set of studies of the decay of HONO and the formation of gas phase products over a range of initial HONO concentrations (0.1-11 ppm) at 1 atm pressure in N 2 at 296 K and 0, 20 and 50% relative humidity (RH), respectively. The loss of HONO and increase in gas phase products were measured over time using long path FTIR spectroscopy. Studies were carried out in an unconditioned borosilicate glass cell and in the same cell after pretreatment with dry gaseous nitric acid. In the HNO 3 -conditioned cell, the loss of HONO was first order at all values of relative humidity (RH), and NO 2 was the only significant gas phase product. For the unconditioned cell, the reaction order increased from first order at 0% RH to second order at 50% RH. The gas phase products at 0% RH were equal amounts of NO and NO 2 . The yield of NO increased to > 90% at 50% RH while the yield of NO 2 decreased to 10%. For both the unconditioned and the HNO 3 -treated cell, the rate of loss of HONO decreased with increasing RH. These results suggest that there is a competition between water, HONO and HNO 3 for surface sites. Displacement of HONO from the cell walls by water was observed in separate experiments. Possible mechanisms, and the implications for HONO formation in environmental chambers and in air, are discussed.

Influence of relative humidity on heterogeneous kinetics of NO2 on kaolin and hematite

“…It should be pointed out that the kinetic data were measured in the dark in this work, and other factors such as adsorbed HNO 3 have not been considered. It is necessary to investigate in the future whether irradiation has an enhancement effect on these reactions like that on Saharan sand 23 and whether the co-absorbed species, such as HNO 3 , which were found to promote HONO decomposition on borosilicate glass surfaces, 49 have an influence on the HONO yield.…”

The photochemical production of HONO during the heterogeneous hydrolysis of NO2

“…This ion pair reacts with surface film water to form adsorbed HONO and HNO 3 . The HNO 3 remains on the surface while HONO is either displaced into the gas phase by the competitive adsorption between water and HONO, 30 or undergoes secondary chemistry to produce gaseous NO, NO 2 , and small amounts of N 2 O. In order for HONO production to be first order in NO 2 , as many previous studies reported, 12,[17][18][19][20][21][22][23][24][25][26] a back reaction involving NO 2 reacting with ONONO 2 must be faster than the competing reaction with water.…”

“…The surface reactions were parameterized as gas phase processes. Because the specific details of the NO 2 heterogeneous hydrolysis mechanism are uncertain, this portion of the model is simplified to have the least number of unknown variables and yet still capture the essence of what is known about the heterogeneous hydrolysis of NO 2 : the reaction is first order in NO 2 and water vapor, 12,[17][18][19][20][21][22][23][24][25][26] there is a competitive adsorption on the surface between H 2 O and HONO, 30 and HONO undergoes heterogeneous reactions on the cell walls to generate NO and NO 2 .…”

“…This laboratory has recently proposed a mechanism for reaction (1) in which dinitrogen tetroxide (N 2 O 4 ) is a key intermediate. 12 A schematic diagram of that mechanism, updated to reflect recent findings, 30,31 is shown in Fig. 1.…”

Complexes of HNO3 and NO3− with NO2 and N2O4, and their potential role in atmospheric HONO formation

“…The present studies also show that the photochemically driven transfer of a hydrogen atom from HNO 3 Furthermore, water has been shown to displace HONO from surfaces into the gas phase in both laboratory and field studies. 107,108 Whether this is a simple competitive adsorption/ desorption process or a chemical reaction with a HONO precursor is not known. However, if a complex such as (HNO 3 )Á(N 2 O 4 ) is a precursor to HONO, the latter may be initially bound to HNO 3 when it is formed on the surface.…”