Injection in the lower stratosphere of biomass fire emissions followed by long-range transport: a MOZAIC case study

Abstract

Abstract. This paper analyses a stratospheric injection by deep convection of biomass fire emissions over North America (Alaska, Yukon and Northwest Territories) on 24 June 2004 and its long-range transport over the eastern coast of the United States and the eastern Atlantic. The case study is based on airborne MOZAIC observations of ozone, carbon monoxide, nitrogen oxides and water vapour during the crossing of the southernmost tip of an upper level trough over the Eastern Atlantic on 30 June and on a vertical profile over Washington DC on 30 June, and on lidar observations of aerosol backscattering at Madison (University of Wisconsin) on 28 June. Attribution of the observed CO plumes to the boreal fires is achieved by backward simulations with a Lagrangian particle dispersion model (FLEXPART). A simulation with the Meso-NH model for the source region shows that a boundary layer tracer, mimicking the boreal forest fire smoke, is lofted into the lowermost stratosphere (2-5 pvu layer) during the diurnal convective cycle at isentropic levels (above 335 K) corresponding to those of the downstream MOZAIC observations. It is shown that the order of magnitude of the time needed by the parameterized convective detrainment flux to fill the volume of a model mesh (20 km horizontal, 500 m vertical) above the tropopause with pure boundary layer air would be about 7.5 h, i.e. a time period compatible with the convective diurnal cycle. Over the area of interest, the maximum instantaneous detrainment fluxes deposited about 15 to 20% of the initial boundary layerCorrespondence to: J.-P. Cammas (jean-pierre.cammas@aero.obs-mip.fr) tracer concentration at 335 K. According to the 275-ppbv carbon monoxide maximum mixing ratio observed by MOZAIC over Eastern Atlantic, such detrainment fluxes would be associated with a 1.4-1.8 ppmv carbon monoxide mixing ratio in the boundary layer over the source region.

Tropospheric ozone and its precursors from the urban to the global scale from air quality to short-lived climate forcer

“…Numerous studies report high mixing ratios of biomass burning products, CO in particular, measured in the middle to upper troposphere and eventually up to the lower stratosphere, thousands of kilometre from the fire sources (e.g. Nedelec et al, 2005;Cammas et al, 2009;Fromm et al, 2010;Elguindi et al, 2010). Biomass burning signatures from Canadian forest fires have also been observed in the lower troposphere at the Pico Observatory on the opposite side of the North Atlantic (Val Martin et al, 2006).…”

The Untold Story of Pyrocumulonimbus

“…With this work we have attempted to reduce the unknowns by revealing several additional occasions when pyroCbs were either a significant or sole cause for the type of stratospheric pollution usually attributed to volcanic injections. Now it is established that pyroCb activity is sufficiently frequent that a measurable stratospheric increase in aerosols attributable to this process occurred in 1989-91, 1992 (Livesey et al 2004), 1998 (Fromm et al 2000(Fromm et al , 2005, and 2001-04 (Fromm et al 2006(Fromm et al , 2008aCammas et al 2009). Unpublished analyses of satellite data (e.g., SAGE II aerosol profiles and imager data) have also revealed pyroCbs and stratospheric aerosol layers that are attributable to the Great China Fire in May 1987 (Cahoon et al 1994) and the Yellowstone fires of 1988 (Alexander 2009).…”

“…Reports of confirmed pyroCbs and stratospheric impact are increasing in the scientific literature, but the entire body of published cases accounts for fewer than 10 events (Jost et al 2004;Livesey et al 2004;Fromm et al 2006;Damoah et al 2006;Lindsey and Fromm 2008;Cammas et al 2009). However, since the advent of the "satellite era" 2 in 1979, several stratospheric mystery-layer events have been reported (e.g., Bluth et al 1997;Clancy 1986;Evans and Kerr 1983).…”

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

“…BB influence can also dominate the abundance of various volatile organic compounds (VOCs) measured at remote background sites . Under certain burning and meteorological conditions, vertical mixing can be dramatically enhanced by fires (known as pyroconvection), allowing rapid transport of pyrogenic species and particulates into the upper troposphere/lower stratosphere (UTLS), resulting in perturbations to the Earth's radiation budget, cloud microphysics and stratospheric chemistry (Damoah et al, 2006;Cammas et al, 2009). However, much work is still needed to fully understand the relative impact of BB on overall atmospheric composition (Wotawa and Trainer, 2000;Monks et al, 2009); a particular area of disagreement in the literature is whether BB results in the net production of tropospheric O 3 (Jaffe and Wigder, 2012;Parrington et al, 2013).…”