Measurements of biomass burning influences in the troposphere over southeast Australia during the SAFARI 2000 dry season campaign

Abstract

[1] Several studies have observed midtropospheric atmospheric composition anomalies and suggested a link to tropical biomass burning. Such anomalies complicate the use of trace gas profiles in remote regions to infer their surface sources/sinks based on the vertical gradients. The Southern African Regional Science Initiative (SAFARI 2000) campaign in Africa and coordinated downwind measurements in Australia provided an opportunity to confirm this link and elucidate the specific surface and atmospheric processes. Five aircraft missions were conducted by Commonwealth Scientific and Industrial Research Organisation (CSIRO) Atmospheric Research during the campaign. They were scheduled after African outflows of polluted air were observed in satellite images over the Indian Ocean flowing east toward Australia. Air samples collected from near the surface to 7 km were analyzed for a suite of trace gases ( 12 CO 2 , CH 4 , CO, H 2 , N 2 O, and C 2 and C 3 hydrocarbons) and one isotopomer ( 13 CO 2 ) to provide vertical composition profiles. Ozone was monitored continuously during flight while a groundbased lidar was employed in the Melbourne region to detect aerosol layers. A preliminary statistical analysis on the Australian data confirms covarying midtroposphere enhancements in the biomass burning products. Making rudimentary corrections for photochemical evolution during transit, the trace gas enhancement ratios in affected air samples are comparable to emission ratios in fresh biomass burning plumes. The 13 CO 2 / 12 CO 2 ratios are also consistent with a source from terrestrial plants. Backtrajectory analysis for strongly enhanced samples suggests long-range transport from tropical regions in Africa or South America, the proof of which requires a follow-on analysis with a global chemistry transport model.

Stratospheric ozone intrusion events and their impacts on tropospheric ozone in the Southern Hemisphere

“…Biomass burning in southern Africa and South America has previously been shown to have a major influence on atmospheric composition in the vicinity of our measurement sites (Oltmans et al, 2001;Gloudemans et al, 2007;Edwards et al, 2006), particularly from July to December (Pak et al, 2003;Liu et al, 2017). On occasion, smoke plumes from Australian and Indonesian fires can also reach the mid-high southern latitudes, as seen from satellite measurements of carbon monoxide (CO) discussed below.…”

Improved method for linear carbon monoxide simulation and source attribution in atmospheric chemistry models illustrated using GEOS-Chem v9

“…As local emissions are generally low, Australasian tropospheric composition is frequently impacted by intercontinental transport of air masses from elsewhere in the Southern Hemisphere (Gloudemans et al, 2006;Zeng et al, 2012;Buchholz et al, 2016). Significant attention has been paid to transported biomass burning plumes (e.g., Pak et al, 2003;Gloudemans et al, 2006;Edwards et al, 2006;Zeng et al, 2012). However, recent work by Buchholz et al (2016) and Té et al (2016) suggests that NMVOC oxidation dominates over biomass burning as a CO source throughout the year in the Australian extratropics and in all months except September-October in the tropics.…”

Plant traits and wood fates across the globe: rotted, burned, or consumed?

“…Combustion releases wood C primarily as CO 2 . However, wildfires also produce small quantities of CO, methane, and elemental C aerosols as well as a complex mixture of organic compounds (Pak et al, 2003;Preston & Schmidt, 2006). In addition to the release of wood C to the atmosphere, fire converts some of the remaining solid mass to char, which oxidizes slowly.…”