A case study of aerosol depletion in a biomass burning plume over Eastern Canada during the 2011 BORTAS field experiment

Abstract

Abstract. We present measurements of a long range smoke transport event recorded on 20–21 July 2011 over Halifax, Nova Scotia, Canada, during the Quantifying the impact of BOReal forest fires on Tropospheric oxidants over the Atlantic using Aircraft and Satellites (BORTAS-B) campaign. Ground-based Fourier transform spectrometers and photometers detected air masses associated with large wildland fires burning in eastern Manitoba and western Ontario. We investigate a plume with high trace gas amounts but low amounts of particles that preceded and overlapped at the Halifax site with a second plume with high trace gas loadings and significant amounts of particulate material. We show that the first plume experienced a meteorological scavenging event but the second plume had not been similarly scavenged. This points to the necessity to account carefully for the plume history when considering long range transport since simultaneous or near-simultaneous times of arrival are not necessarily indicative of either similar trajectories or meteorological history. We investigate the origin of the scavenged plume, and the possibility of an aerosol wet deposition event occurring in the plume ~24 h prior to the measurements over Halifax. The region of lofting and scavenging is only monitored on an intermittent basis by the present observing network, and thus we must consider many different pieces of evidence in an effort to understand the early dynamics of the plume. Through this discussion we also demonstrate the value of having many simultaneous remote-sensing measurements in order to understand the physical and chemical behaviour of biomass burning plumes.

Investigation of CO, C<sub>2</sub>H<sub>6</sub> and aerosols in a boreal fire plume over eastern Canada during BORTAS 2011 using ground- and satellite-based observations and model simulations

“…The DAO-DA8 FTS at DGS is a vertically aligned Michelson interferometer (Franklin et al, 2013). It is equipped with InSb and HgCdTe detectors and a potassium bromide (KBr) beam splitter to provide spectral coverage between 750 and 4500 cm −1 .…”

“…However, on 20 July, the CO and C 2 H 6 columns are high but the AOD is not significantly enhanced. The reason for this is likely a precipitation event (Franklin et al, 2013) in which most aerosols were removed, while the trace gas column stayed enhanced. After excluding data from this day, the simultaneous CO columns and the fine-mode AOD are highly correlated (R 2 ≈ 0.8), with a slope of (1.22 ± 0.04) × 10 18 molec cm −2 per unit increase in fine-mode AOD and an intercept of (1.76 ± 0.01) × 10 18 molec cm −2 .…”

Ozone photochemistry in boreal biomass burning plumes

“…Low aerosol loading and low RH may be explained by these more aged air masses having experienced precipitation events during transport from the emission source region. Analysis of ground-based remote sensing measurements made from Halifax, NS, during the BORTAS campaign period identified a biomass burning plume with relatively low fine mode aerosol optical depth correlated with enhanced CO total columns, which was attributable to precipitation along the plume trajectory (Griffin et al, 2013;Franklin et al, 2013).…”

Ozone photochemistry in boreal biomass burning plumes

“…Low aerosol loading and low RH may be explained by these more aged air masses having experienced precipitation events during transport from the emission source region. Analysis of ground-based remote sensing measurements made from Halifax, NS, during the BORTAS campaign period identified a biomass burning plume with relatively low fine mode aerosol optical depth correlated with enhanced CO total columns, which was attributable to precipitation along the plume trajectory Franklin et al, 2013).…”