Observations of nonmethane organic compounds during ARCTAS − Part 1: Biomass burning emissions and plume enhancements

Abstract

Abstract. Mixing ratios of a large number of nonmethane organic compounds (NMOCs) were observed by the Trace Organic Gas Analyzer (TOGA) on board the NASA DC-8 as part of the Arctic Research of the Composition of the Troposphere from Aircraft and Satellites (ARCTAS) field campaign. Many of these NMOCs were observed concurrently by one or both of two other NMOC measurement techniques on board the DC-8: proton-transfer-reaction mass spectrometry (PTR-MS) and whole air canister sampling (WAS). A comparison of these measurements to the data from TOGA indicates good agreement for the majority of co-measured NMOCs. The ARCTAS study, which included both spring and summer deployments, provided opportunities to sample a large number of biomass burning (BB) plumes with origins in Asia, California and central Canada, ranging from very recent emissions to plumes aged one week or more. For this analysis, BB smoke interceptions were grouped by flight, source region and, in some cases, time of day, generating 40 identified BB plumes for analysis. Normalized excess mixing ratios (NEMRs) to CO were determined for each of the 40 plumes for up to 19 different NMOCs or NMOC groups. Although the majority of observed NEMRs for individual NMOCs or NMOC groups were in agreement with previously-reported values, the observed NEMRs to CO for ethanol, a rarely quantified gas-phase trace gas, ranged from values similar to those previously reported, to up to Correspondence to: R. S. Hornbrook (rsh@ucar.edu) an order of magnitude greater. Notably, though variable between plumes, observed NEMRs of individual light alkanes are highly correlated within BB emissions, independent of estimated plume ages. BB emissions of oxygenated NMOC were also found to be often well-correlated. Using the NCAR Master Mechanism chemical box model initialized with concentrations based on two observed scenarios, fresh Canadian BB and fresh Californian BB, decreases are predicted for the low molecular weight carbonyls (i.e. formaldehyde, acetaldehyde, acetone and methyl ethyl ketone, MEK) and alcohols (i.e. methanol and ethanol) as the plumes evolve in time, i.e. the production of these compounds is less than the chemical loss. Comparisons of the modeled NEMRs to the observed NEMRs from BB plumes estimated to be three days in age or less indicate overall good agreement.

Quantification of hydroxyacetone and glycolaldehyde using chemical ionization mass spectrometry

“…These ratios were determined for fires with different plume ages and various fuel types. Post-emission chemistry is expected to affect enhancement ratios, and Hornbrook et al (2011). previous work has observed an increase in glycolaldehyde relative to CO with plume age (Akagi et al, 2012). The ARCTAS-CARB observations are consistent with the previously reported observations of glycolaldehyde in biomassburning plumes.…”

“…A list of biomass- burning plumes encountered by the DC-8 during the ARC-TAS campaign can be found in Hornbrook et al (2011). Possible biomass-burning plumes are identified by time periods of elevated biomass-burning tracer mixing ratios.…”

Airborne observations of trace gases over boreal Canada during BORTAS: campaign climatology, air mass analysis and enhancement ratios

“…These lifetimes are also short enough so that BB emissions are a substantial increase over the ambient concentrations. For these reasons all three species are widely used tracers for BB Hornbrook et al, 2011;Vay et al, 2011).…”

Spectral absorption of biomass burning aerosol determined from retrieved single scattering albedo during ARCTAS

“…Maximum concentrations of these biomass burning tracers as well as plume altitudes are listed in Table 1. Plume identification and back trajectory analysis performed by Hornbrook et al (2011) indicated the 17 April plume examined here was a ∼ 6 day old Siberian forest fire plume. In contrast, measurements during the 29 June case were made directly above an active fire in Saskatchewan, a plume less than 3 h old (Hornbrook et al, 2011).…”

“…Plume identification and back trajectory analysis performed by Hornbrook et al (2011) indicated the 17 April plume examined here was a ∼ 6 day old Siberian forest fire plume. In contrast, measurements during the 29 June case were made directly above an active fire in Saskatchewan, a plume less than 3 h old (Hornbrook et al, 2011). It is important to note that the 17 April plume was intersected at the top of the spiral profile and it is unclear whether the entire plume was sampled.…”