Nitrogen oxides and PAN in plumes from boreal fires during ARCTAS-B and their impact on ozone: an integrated analysis of aircraft and satellite observations

We determine enhancement ratios for NO<sub>x</sub>, PAN, and other NO<sub>y</sub> species from boreal biomass burning using aircraft data obtained during the ARCTAS-B campaign and examine the impact of these emissions on tropospheric ozone in the Arctic. We find an initial emission factor for NO<sub>x</sub> of 1.06 g NO per kg dry matter (DM) burned, much lower than previous observations of boreal plumes, and also one third the value recommended for extratropical fires. Our analysis provides the first observational confirmation of rapid PAN formation in a boreal smoke plume, with 40% of the initial NO<sub>x</sub> emissions being converted to PAN in the first few hours after emission. We find little clear evidence for ozone formation in the boreal smoke plumes during ARCTAS-B in either aircraft or satellite observations, or in model simulations. Only a third of the smoke plumes observed by the NASA DC8 showed a correlation between ozone and CO, and ozone was depleted in the plumes as often as it was enhanced. Special observations from the Tropospheric Emission Spectrometer (TES) also show little evidence for enhanced ozone in boreal smoke plumes between 15 June and 15 July 2008. Of the 22 plumes observed by TES, only 4 showed ozone increasing within the smoke plumes, and even in those cases it was unclear that the increase was caused by fire emissions. Using the GEOS-Chem atmospheric chemistry model, we show that boreal fires during ARCTAS-B had little impact on the median ozone profile measured over Canada, and had little impact on ozone within the smoke plumes observed by TES

Mutation D816V Alters the Internal Structure and Dynamics of c-KIT Receptor Cytoplasmic Region: Implications for Dimerization and Activation Mechanisms

The type III receptor tyrosine kinase (RTK) KIT plays a crucial role in the transmission of cellular signals through phosphorylation events that are associated with a switching of the protein conformation between inactive and active states. D816V KIT mutation is associated with various pathologies including mastocytosis and cancers. D816V-mutated KIT is constitutively active, and resistant to treatment with the anti-cancer drug Imatinib. To elucidate the activating molecular mechanism of this mutation, we applied a multi-approach procedure combining molecular dynamics (MD) simulations, normal modes analysis (NMA) and binding site prediction. Multiple 50-ns MD simulations of wild-type KIT and its mutant D816V were recorded using the inactive auto-inhibited structure of the protein, characteristic of type III RTKs. Computed free energy differences enabled us to quantify the impact of D816V on protein stability in the inactive state. We evidenced a local structural alteration of the activation loop (A-loop) upon mutation, and a long-range structural re-organization of the juxta-membrane region (JMR) followed by a weakening of the interaction network with the kinase domain. A thorough normal mode analysis of several MD conformations led to a plausible molecular rationale to propose that JMR is able to depart its auto-inhibitory position more easily in the mutant than in wild-type KIT and is thus able to promote kinase mutant dimerization without the need for extra-cellular ligand binding. Pocket detection at the surface of NMA-displaced conformations finally revealed that detachment of JMR from the kinase domain in the mutant was sufficient to open an access to the catalytic and substrate binding sites

Potential Role of Stabilized Criegee Radicals in Sulfuric Acid Production in a High Biogenic VOC Environment

We present field observations made in June 2011 downwind of Dallas-Fort Worth, TX, and evaluate the role of stabilized Criegee radicals (sCIs) in gaseous sulfuric acid (H2SO4) production. Zero-dimensional model calculations show that sCI from biogenic volatile organic compounds composed the majority of the sCIs. The main uncertainty associated with an evaluation of H2SO4 production from the sCI reaction channel is the lack of experimentally determined reaction rates for sCIs formed from isoprene ozonolysis with SO2 along with systematic discrepancies in experimentally derived reaction rates between other sCIs and SO2 and water vapor. In general, the maximum of H2SO4 production from the sCI channel is found in the late afternoon as ozone increases toward the late afternoon. The sCI channel, however, contributes minor H2SO4 production compared with the conventional OH channel in the mid-day. Finally, the production and the loss rates of H2SO4 are compared. The application of the recommended mass accommodation coefficient causes significant overestimation of H2SO4 loss rates compared with H2SO4 production rates. However, the application of a lower experimental value for the mass accommodation coefficient provides good agreement between the loss and production rates of H2SO4. The results suggest that the recommended coefficient for the H2O surface may not be suitable for this relatively dry environment

On the volatility and production mechanisms of newly formed nitrate and water soluble organic aerosol in Mexico City

Measurements of atmospheric gases and fine par- ticle chemistry were made in the Mexico City Metropolitan Area (MCMA) at a site ∼ 30 km down wind of the city cen- ter. Ammonium nitrate (NH 4 NO 3 ) dominated the inorganic aerosol fraction and showed a distinct diurnal signature char- acterized by rapid morning production and a rapid mid-day concentration decrease. Between the hours of 08:00–12:45, particulate water-soluble organic carbon (WSOC) concentra- tions increased and decreased in a manner consistent with that of NO − 3 , and the two were highly correlated ( R 2 =0.88) during this time. A box model was used to analyze these be- haviors and showed that, for both NO − 3 and WSOC, the con- centration increase was caused primarily ( ∼ 75–85%) by sec- ondary formation, with a smaller contribution ( ∼ 15–25%) from the entrainment of air from the free troposphere. For NO − 3 , a majority ( ∼ 60%) of the midday concentration de- crease was caused by dilution from boundary layer expan- sion, though a significant fraction ( ∼ 40%) of the NO − 3 loss was due to particle evaporation. The WSOC concen- tration decrease was due largely to dilution ( ∼ 75%), but volatilization did have a meaningful impact ( ∼ 25%) on the decrease, as well. The results provide an estimate of ambient SOA evaporation losses and suggest that a significant frac- tion ( ∼ 35%) of the fresh MCMA secondary organic aerosol (SOA) measured at the surface volatilized

On the volatility and production mechanisms of newly formed nitrate and water soluble organic aerosol in Mexico City

Measurements of atmospheric gases and fine particle chemistry were made in the Mexico City Metropolitan Area (MCMA) at a site ∼30 km down wind of the city center. Ammonium nitrate (NH4NO3) dominated the inorganic aerosol fraction and showed a distinct diurnal signature characterized by rapid morning production and a rapid mid-day concentration decrease. Between the hours of 08:00ĝ€"12:45, particulate water-soluble organic carbon (WSOC) concentrations increased and decreased in a manner consistent with that of NO3−, and the two were highly correlated (R2=0.88) during this time. A box model was used to analyze these behaviors and showed that, for both NO3− and WSOC, the concentration increase was caused primarily (∼75ĝ€"85%) by secondary formation, with a smaller contribution (∼15ĝ€"25%) from the entrainment of air from the free troposphere. For NO3 −, a majority (∼60%) of the midday concentration decrease was caused by dilution from boundary layer expansion, though a significant fraction (∼40%) of the NO3− loss was due to particle evaporation. The WSOC concentration decrease was due largely to dilution (∼75%), but volatilization did have a meaningful impact (∼25%) on the decrease, as well. The results provide an estimate of ambient SOA evaporation losses and suggest that a significant fraction (∼35%) of the fresh MCMA secondary organic aerosol (SOA) measured at the surface volatilized

Nitrogen oxides and PAN in plumes from boreal fires during ARCTAS-B and their impact on ozone: An integrated analysis of aircraft and satellite observations

We determine enhancement ratios for NOx, PAN, and other NO y species from boreal biomass burning using aircraft data obtained during the ARCTAS-B campaign and examine the impact of these emissions on tropospheric ozone in the Arctic. We find an initial emission factor for NO x of 1.06 g NO per kg dry matter (DM) burned, much lower than previous observations of boreal plumes, and also one third the value recommended for extratropical fires. Our analysis provides the first observational confirmation of rapid PAN formation in a boreal smoke plume, with 40% of the initial NOx emissions being converted to PAN in the first few hours after emission. We find little clear evidence for ozone formation in the boreal smoke plumes during ARCTAS-B in either aircraft or satellite observations, or in model simulations. Only a third of the smoke plumes observed by the NASA DC8 showed a correlation between ozone and CO, and ozone was depleted in the plumes as often as it was enhanced. Special observations from the Tropospheric Emission Spectrometer (TES) also show little evidence for enhanced ozone in boreal smoke plumes between 15 June and 15 July 2008. Of the 22 plumes observed by TES, only 4 showed ozone increasing within the smoke plumes, and even in those cases it was unclear that the increase was caused by fire emissions. Using the GEOS-Chem atmospheric chemistry model, we show that boreal fires during ARCTAS-B had little impact on the median ozone profile measured over Canada, and had little impact on ozone within the smoke plumes observed by TES. © 2010 Author(s)