OHNO decompositionon borosilicate glass surfaces:implications for environmental chamber studies and field experiments.

摘要

Nitrous acid (HONO) is the major source of OH in poolluted urban atomospheres,so an understanding of its fromation and loss processes both in urban atmospheres and in laboratory systems is important.Earlier studies over a range of initial HONO concnetrations ( 0.1-0.11ppm) at 1 atm pressure in N_2 at 296 K and 0,20 and 50% relative humidity(RH),espectively.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 te only significant gas phase product.For the unconditoned cell,thereaction order increased form 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 boththe unconditioned and the HNO_3-treated cell,the rate of loss of HONO decreased iwthincreasing 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 idscussed.