Trace gas emissions from a mid‐latitude prescribed chaparral fire

Abstract

Gas samples were collected in smoke plumes over the San Dimas Experimental Forest during a 400‐acre prescribed chaparral fire on December 12, 1986. A helicopter was used to collect gas samples over areas of vigorous flaming combustion and over areas of mixed stages (vigorous/transitional/smoldering) of combustion. Sampling was conducted at altitudes as low as 35 m and as high as 670 m above ground level. The samples, collected in 20‐L Tedlar bags, were returned by helicopter to our field laboratory and immediately transferred to electropolished stainless steel canisters. Analyses for the trace gases carbon dioxide (CO 2 ), carbon monoxide (CO), hydrogen (H 2 ), methane (CH 4 ), total nonmethane hydrocarbons (TNMHC), and nitrous oxide (N 2 O) were performed within hours after collection. Samples of gas were also collected upwind of the burn and analyzed to determine ambient background levels. Mean emission ratios (Δ X /ΔCO 2 , where X is equal to each species, vol/vol) determined for these gases relative to CO 2 were generally lower (except for N 2 O) than mean emission ratios previously reported for large biomass‐burning field experiments. No substantial differences in CO 2 normalized emission ratios for these gases (except for N 2 O) were determined when samples from vigorously flaming and mixed stages of combustion were compared. Emissions from flaming portions of chaparral, however, would be expected to release disporportionately larger volumes of trace gases into the sampled smoke plumes. This, coupled with the very high surface‐to‐volume fuel ratio typical of a chaparral fire (which minimizes the smoldering stage), may have accounted for the consistency in the emission ratios.