Quantifying the impact of BOReal forest fires on Tropospheric oxidants over the Atlantic using Aircraft and Satellites (BORTAS) experiment: design, execution and science overview

Abstract

We describe the design and execution of the BORTAS (Quantifying the impact of BOReal forest fires on Tropospheric oxidants over the Atlantic using Aircraft and Satellites) experiment, which has the overarching objective of understanding the chemical aging of air masses that contain the emission products from seasonal boreal wildfires and how these air masses subsequently impact downwind atmospheric composition. The central focus of the experiment was a two-week deployment of the UK BAe-146-301 Atmospheric Research Aircraft (ARA) over eastern Canada, based out of Halifax, Nova Scotia. Atmospheric ground-based and sonde measurements over Canada and the Azores associated with the planned July 2010 deployment of the ARA, which was postponed by 12 months due to UK-based flights related to the dispersal of material emitted by the Eyjafjallajökull volcano, went ahead and constituted phase A of the experiment. Phase B of BORTAS in July 2011 involved the same atmospheric measurements, but included the ARA, special satellite observations and a more comprehensive ground-based measurement suite. The high-frequency aircraft data provided a comprehensive chemical snapshot of pyrogenic plumes from wildfires, corresponding to photochemical (and physical) ages ranging from < 1 day to ~<span style="position: relative; top: -.5em; left: -.80em;"><</span><i style=" margin-left:-.7em"></i>45 sr 10 days, largely by virtue of widespread fires over Northwestern Ontario. Airborne measurements reported a large number of emitted gases including semi-volatile species, some of which have not been been previously reported in pyrogenic plumes, with the corresponding emission ratios agreeing with previous work for common gases. Analysis of the NO_y data shows evidence of net ozone production in pyrogenic plumes, controlled by aerosol abundance, which increases as a function of photochemical age. The coordinated ground-based and sonde data provided detailed but spatially limited information that put the aircraft data into context of the longer burning season in the boundary layer. Ground-based measurements of particulate matter smaller than 2.5 μm (PM_2.5) over Halifax show that forest fires can on an episodic basis represent a substantial contribution to total surface PM_2.5

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

“…As reported by Palmer et al (2013) fire activity during the BORTAS sampling period was dominated by widespread fires in northwestern Ontario. Extensive fires in this region took place from 17 to 19 July 2011, plumes from which were sampled over 1000 km downwind during measurement flights B621 to B624 (18 to 21 July 2011, Sect.…”

“…A common method to identify BB plumes is to use some combination of HCN, CH 3 CN and CO to partition air masses between those that have, and those that have not, been recently influenced by biomass burning (Hornbrook et al, 2011;Vay et al, 2011;Palmer et al, 2013). A representative threshold concentration value and/or ratio is chosen from tracer-tracer relationships, where the tracer measurements above a certain threshold value are classified as a biomass burning plume.…”

“…The UK's Facility for Airborne Atmospheric Measurements (FAAM) BAe-146 research aircraft was deployed to Nova Scotia, Canada, where a number of BB plumes of differing ages were sampled (0 to 10 days). A comprehensive description of the motivation for the BORTAS experiment can be found in Palmer et al (2013), along with a description of the FAAM BAe-146 instrumental payload, a general summary of the flights that took place during BORTAS, and the prevailing synoptic meteorological conditions. This paper presents the in situ observations of CO 2 and CH 4 that were made using cavity-enhanced absorption spectroscopy on the FAAM BAe-146 as part of the BORTAS project.…”

“…CH 3 CN concentrations were determined using a proton transfer reaction mass spectrometer (PTR-MS), with a 9 to 20 s time response depending on the number of species that are measured, and the CH 3 CN measurement uncertainty is estimated to be ±9 % (Murphy et al, 2010). For a description of all other measurements made on the FAAM BAe-146 refer to Palmer et al (2013).…”

Quantifying pyroconvective injection heights using observations of fire energy: sensitivity of spaceborne observations of carbon monoxide

“…Palmer et al, 2013, and articles therein). Strictly speaking, pure pyroconvection is rare, with most events triggered by storm systems that can result in unstable atmospheric conditions and enhance the vertical extent of the mixing due to the fire (e.g.…”