Reactive uptake coefficients for N2O5 determined from aircraft measurements during the Second Texas Air Quality Study: Comparison to current model parameterizations

This paper presents determinations of reactive uptake coefficients for N 2 O 5 , γ (N 2 O 5 ), on aerosols from nighttime aircraft measurements of ozone, nitrogen oxides, and aerosol surface area on the NOAA P‐3 during Second Texas Air Quality Study (TexAQS II). Determinations based on both the steady state approximation for NO 3 and N 2 O 5 and a plume modeling approach yielded γ (N 2 O 5 ) substantially smaller than current parameterizations used for atmospheric modeling and generally in the range 0.5–6 × 10 −3 . Dependence of γ (N 2 O 5 ) on variables such as relative humidity and aerosol composition was not apparent in the determinations, although there was considerable scatter in the data. Determinations were also inconsistent with current parameterizations of the rate coefficient for homogenous hydrolysis of N 2 O 5 by water vapor, which may be as much as a factor of 10 too large. Nocturnal halogen activation via conversion of N 2 O 5 to ClNO 2 on chloride aerosol was not determinable from these data, although limits based on laboratory parameterizations and maximum nonrefractory aerosol chloride content showed that this chemistry could have been comparable to direct production of HNO 3 in some cases.