Trace gas emissions from savanna fires in northern Australia

We present analyses of near‐infrared ground‐based Fourier transform infrared solar

absorption spectra recorded from a site in Darwin, Northern Territory, Australia

(12.4°S, 130.9°E) from August 2005 to June 2008. Total column amounts of carbon

monoxide derived from these spectra show a very clear annual cycle, with evidence of

transported pollution from Indonesian fires in 2006. Aerosol optical depth measurements

from the same site show a similar annual cycle but without exceptional values in 2006,

suggesting significant loss of aerosol loading in the transported and aged smoke. In

addition, we report the first ever measurements by remote sensing solar Fourier transform

infrared of emission ratios with respect to carbon monoxide for formaldehyde

(0.022 ± 0.007), acetylene (0.0024 ± 0.0003), ethane (0.0020 ± 0.0003), and hydrogen

cyanide (0.0018 ± 0.0003) from Australian savanna fires. These are derived from

mid‐infrared spectra recorded through smoke plumes over Darwin on 20 separate days.

The only previous measurements of emission ratios for formaldehyde and hydrogen

cyanide from Australian savanna fires involved cryogenic trapping and storage of samples

that were gathered in very fresh smoke. The results reported here are nearly an order of

magnitude higher (but in agreement with laboratory studies), suggesting losses in the

collection, storage, or transfer of the gases in the earlier measurements and/or chemical

production of these reactive gases within the smoke plumes. Emission ratios for acetylene

and ethane from this work are in broad agreement with other literature values.