Airborne Observations Constrain Heterogeneous Nitrogen and Halogen Chemistry on Tropospheric and Stratospheric Biomass Burning Aerosol

Abstract

Heterogeneous chemical cycles of pyrogenic nitrogen and halides influence tropospheric ozone and affect the stratosphere during extreme Pyrocumulonimbus (PyroCB) events. We report field‐derived N2O5 uptake coefficients, γ(N2O5), and ClNO2 yields, φ(ClNO2), from two aircraft campaigns observing fresh smoke in the lower and mid troposphere and processed/aged smoke in the upper troposphere and lower stratosphere (UTLS). Derived φ(ClNO2) varied across the full 0–1 range but was typically <0.5 and smallest in a PyroCB (<0.05). Derived γ(N2O5) was low in agricultural smoke (0.2–3.6 × 10−3), extremely low in mid‐tropospheric wildfire smoke (0.1 × 10−3), but larger in PyroCB processed smoke (0.7–5.0 × 10−3). Aged biomass burning aerosol in the UTLS had a higher γ(N2O5) of 17 × 10−3 that increased with sulfate and liquid water, but that was 1–2 orders of magnitude lower than values for aqueous sulfuric aerosol used in stratospheric models.

Emissions and Atmospheric Chemistry of Furanoids from Biomass Burning: Insights from Laboratory to Atmospheric Observations

“…Cl chemistry is expected to be a minor atmospheric loss process for furanoids, and Cl mixing ratios in smoke are generally low. 153 However, additional room-temperature, and pressure-dependent kinetic studies would provide further insight into furanoid atmospheric degradation mechanisms and the contribution of the H atom abstraction pathway to the overall rate coefficient.…”

“…The Cl atmospheric degradation of furanoids is not expected to be a significant tropospheric loss, though the detection of chlorinated compounds may serve as tracers for this chemistry . There are a few studies that have reported gas-phase products and proposed reaction mechanisms for Cl-addition and H-abstraction pathways. ,,, All studies have been performed at room-temperature (296 ± 2 K) and atmospheric-pressure (1000 ± 20 mbar) conditions in smog chambers.…”