1 research outputs found
A Large Underestimate of Formic Acid from Tropical Fires: Constraints from Space-Borne Measurements
Formic acid (HCOOH) is one of the
most abundant carboxylic acids
and a dominant source of atmospheric acidity. Recent work indicates
a major gap in the HCOOH budget, with atmospheric concentrations much
larger than expected from known sources. Here, we employ recent space-based
observations from the Tropospheric Emission Spectrometer with the
GEOS-Chem atmospheric model to better quantify the HCOOH source from
biomass burning, and assess whether fire emissions can help close
the large budget gap for this species. The space-based data reveal
a severe model HCOOH underestimate most prominent over tropical burning
regions, suggesting a major missing source of organic acids from fires.
We develop an approach for inferring the fractional fire contribution
to ambient HCOOH and find, based on measurements over Africa, that
pyrogenic HCOOH:CO enhancement ratios are much higher than expected
from direct emissions alone, revealing substantial secondary organic
acid production in fire plumes. Current models strongly underestimate
(by 10 ± 5 times) the total primary and secondary HCOOH source
from African fires. If a 10-fold bias were to extend to fires in other
regions, biomass burning could produce 14 Tg/a of HCOOH in the tropics
or 16 Tg/a worldwide. However, even such an increase would only represent
15–20% of the total required HCOOH source, implying the existence
of other larger missing sources