High spectral resolution solar absorption measurements of ethylene (C2H4) in a forest fire smoke plume using HITRAN parameters: Tropospheric vertical profile retrieval

The tropospheric mixing ratio profile of ethylene (C2H4) has been retrieved from a high spectral resolution ground-based infrared solar absorption spectrum. The spectrum was recorded during intense fires in New South Wales, Australia on January 1, 2002, and was analyzed with the C2H4 spectral parameters added to the 2000 HITRAN compilation. Absorption by C2H4 in the smoke-affected spectrum extends over a broad spectral range in a region with observable rotational fine structure. The fine structure occurs in addition to the 949.5cm-1ν7 band Q branch that is traditionally used to quantify C2H4 amounts from infrared atmospheric measurements assuming room temperature laboratory absorption coefficients. The measured spectrum is fitted to near the noise level with a retrieved vertical column of (3.8±0.2)×1017 molecules per square centimeter. The retrieved vertical C2H4 profile increases with altitude near the surface reaching a maximum of 37 parts per billion (10-9) near 1 km, decreasing above.