Airborne Remote Sensing Measurements of HONO Emission Factors

Abstract:

The formation of secondary pollutants, such as ozone and secondary organic aerosols (SOA), in biomass burning smoke is largely driven by hydroxyl radical chemistry. Nitrous acid (HONO) is believed to be an important precursor of hydroxyl radicals early in biomass burning plumes and, therefore, has a significant impact on the photochemistry of smoke plumes. However, there remain considerable uncertainties regarding HONO emission rates by natural fires.

HONO quickly photolyzes after emission from biomass burning, and it is difficult to make in-situ measurmens of HONO emission factors before some photolysis has occured. Here, we will present data from the UCLA Mini-DOAS (Differential Optical Absorption Spectroscopy) instrument, an airborne remote sensing instrument that measured UV-Vis absorbers onboard NASA's DC8 aricraft during the FIREX-AQ campaign in the Summer of 2019. Nadir measurements performed while flying over smoke plumes allow for the observation of fresh smoke directly emitted from burning zones.

We will present HONO emission ratios for a variety of Western wildfires and Eastern crop burning fires and investigate links between HONO emission and fire parameters, such as modified combustion efficiency, fuel type, fire weather, and fire radiative power. These results will help better understand HONO emissions and radical chemistry of biomass burning plumes and improve our ability to model secondary pollutant production in fire models.