Ozone photochemistry in boreal biomass burning plumes

Journal of Geophysical Research, 2007

1] A case of long-range transport of a biomass burning plume from Alaska to Europe is analyzed using a Lagrangian approach. This plume was sampled several times in the free troposphere over North America, the North Atlantic and Europe by three different aircraft during the IGAC Lagrangian 2K4 experiment which was part of the ICARTT/ ITOP measurement intensive in summer 2004. Measurements in the plume showed enhanced values of CO, VOCs and NO y , mainly in form of PAN. Observed O 3 levels increased by 17 ppbv over 5 days. A photochemical trajectory model, CiTTyCAT, was used to examine processes responsible for the chemical evolution of the plume. The model was initialized with upwind data and compared with downwind measurements. The influence of high aerosol loading on photolysis rates in the plume was investigated using in situ aerosol measurements in the plume and lidar retrievals of optical depth as input into a photolysis code (Fast-J), run in the model. Significant impacts on photochemistry are found with a decrease of 18% in O 3 production and 24% in O 3 destruction over 5 days when including aerosols. The plume is found to be chemically active with large O 3 increases attributed primarily to PAN decomposition during descent of the plume toward Europe. The predicted O 3 changes are very dependent on temperature changes during transport and also on water vapor levels in the lower troposphere which can lead to O 3 destruction. Simulation of mixing/dilution was necessary to reproduce observed pollutant levels in the plume. Mixing was simulated using background concentrations from measurements in air masses in close proximity to the plume, and mixing timescales (averaging 6.25 days) were derived from CO changes. Observed and simulated O 3 /CO correlations in the plume were also compared in order to evaluate the photochemistry in the model. Observed slopes change from negative to positive over 5 days. This change, which can be attributed largely to photochemistry, is well reproduced by multiple model runs even if slope values are slightly underestimated suggesting a small underestimation in modeled photochemical O 3 production. The possible impact of this biomass burning plume on O 3 levels in the European boundary layer was also examined by running the model for a further 5 days and comparing with data collected at surface sites, such as Jungfraujoch, which showed small O 3 increases and elevated CO levels. The model predicts significant changes in O 3 over the entire 10 day period due to photochemistry but the signal is largely lost because of the effects of dilution. However, measurements in several other BB plumes over Europe show that O 3 impact of Alaskan fires can be potentially significant over Europe.

2009

We examine the photochemical processes governing the production of ozone in smoke from large Siberian fires that formed in July 2006 using co-located O 3 and CO profiles as measured by the Tropospheric Emission Spectrometer (TES) as well as NO 2 and aerosol optical depths as measured by the Ozone Monitoring Instrument (OMI). The Real-time Air Quality Model (RAQMS) is used to explain the observed variations of O 3 . Enhanced levels of ozone up to 90 parts per billion (ppbv) are observed near and away from the Siberian fires (60 o N and 100 o E) when sunlight and NOx are available. We also observe significantly low O 3 amounts (less then 30 ppbv) in the smoke plume from Siberian fires in conjunction with optically thick aerosols. Despite this wide variance in observed ozone values, the mean ozone value for all observations of the smoke plume is close to background levels of approximately 55 ppbv in the free troposphere. Using RAQMS we show that optically thick aerosols in the smoke plume can substantially reduce the photochemical production of ozone and this can explain why the observed mean ozone amount for all plume observations is not much larger than background values of 55 ppbv. However, the anonymously low ozone amounts of 30 ppbv or less point towards other unresolved processes that reduce ozone below background levels in the plume. 3

Journal of Geophysical Research, 2006

Extensive wildfires burned in northern North America during summer 2004, releasing large amounts of trace gases and aerosols into the atmosphere. Emissions from these wildfires frequently impacted the PICO-NARE station, a mountaintop site situated 6-15 days downwind from the fires in the Azores Islands. To assess the impacts of the boreal wildfire emissions on the levels of aerosol black carbon (BC), nitrogen oxides and O 3 downwind from North America, we analyzed measurements of CO, BC, total reactive nitrogen oxides (NO y), NO x (NO + NO 2) and O 3 made from June to September 2004 in combination with MOZART chemical transport model simulations. Long-range transport of boreal wildfire emissions resulted in large enhancements of CO, BC, NO y and NO x , with levels up to 250 ppbv, 665 ng m À3 , 1100 pptv and 135 pptv, respectively. Enhancement ratios relative to CO were variable in the plumes sampled, most likely because of variations in wildfire emissions and removal processes during transport. Analyses of DBC/DCO, DNO y /DCO and DNO x /DCO ratios indicate that NO y and BC were on average efficiently exported in these plumes and suggest that decomposition of PAN to NO x was a significant source of NO x. High levels of NO x suggest continuing formation of O 3 in these well-aged plumes. O 3 levels were also significantly enhanced in the plumes, reaching up to 75 ppbv. Analysis of DO 3 /DCO ratios showed distinct behaviors of O 3 in the plumes, which varied from significant to lower O 3 production. We identify several potential reasons for the complex effects of boreal wildfire emissions on O 3 and conclude that this behavior needs to be explored further in the future. These observations demonstrate that boreal wildfire emissions significantly contributed to the NO x and O 3 budgets in the central North Atlantic lower free troposphere during summer 2004 and imply large-scale impacts on direct radiative forcing of the atmosphere and on tropospheric NO x and O 3 .

We determine enhancement ratios for NO x , 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 NO x 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.

Atmospheric Chemistry and Physics, 2012

We have analysed the sensitivity of the tropospheric ozone distribution over North America and the North Atlantic to boreal biomass burning emissions during the summer of 2010 using the GEOS-Chem 3-D global tropospheric chemical transport model and observations from in situ and satellite instruments. We show that the model ozone distribution is consistent with observations from the Pico Mountain Observatory in the Azores, ozonesondes across Canada, and the Tropospheric Emission Spectrometer (TES) and Infrared Atmospheric Sounding Instrument (IASI) satellite instruments. Mean biases between the model and observed ozone mixing ratio in the free troposphere were less than 10 ppbv. We used the adjoint of GEOS-Chem to show the model ozone distribution in the free troposphere over Maritime Canada is largely sensitive to NO x emissions from biomass burning sources in Central Canada, lightning sources in the central US, and anthropogenic sources in the eastern US and southeastern Canada. We also used the adjoint of GEOS-Chem to evaluate the Fire Locating And Monitoring of Burning Emis-sions (FLAMBE) inventory through assimilation of CO observations from the Measurements Of Pollution In The Troposphere (MOPITT) satellite instrument. The CO inversion showed that, on average, the FLAMBE emissions needed to be reduced to 89 % of their original values, with scaling factors ranging from 12 % to 102 %, to fit the MOPITT observations in the boreal regions. Applying the CO scaling factors to all species emitted from boreal biomass burning sources led to a decrease of the model tropospheric distributions of CO, PAN, and NO x by as much as −20 ppbv, −50 pptv, and −20 pptv respectively. The modification of the biomass burning emission estimates reduced the model ozone distribution by approximately −3 ppbv (−8 %) and on average improved the agreement of the model ozone distribution compared to the observations throughout the free troposphere, reducing the mean model bias from 5.5 to 4.0 ppbv for the Pico Mountain Observatory, 3.0 to 0.9 ppbv for ozonesondes, 2.0 to 0.9 ppbv for TES, and 2.8 to 1.4 ppbv for IASI.

Atmospheric Chemistry and Physics, 2013

ABSTRACT We describe the design and execution of the BORTAS (Quantifying the impact of BOReal forest fires on Tropospheric oxidants using Aircraft and Satellites) experiment, which has the overarching objective of understanding the chemical aging of airmasses, containing the emission products from seasonal boreal wildfires, and how they 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. This was complemented by ground-based measurements at the Dalhousie University Ground Station (DGS) and the University of Toronto, enhanced ozonesonde launches, measurements on the Pico Mountain Atmospheric Observatory in the Azores, and coordinated space-borne measurements. Integration of these data has helped us to describe pollution plumes from wildfires on a wide spectrum of temporal and spatial scales. These data are interpreted using a range of chemistry models, from a near-explicit gas-phase chemical mechanism to a regional and global model of atmospheric transport and lumped chemistry, and data assimilation tools. We also provide a brief science overview of the project, providing the platform for co-submitted science abstracts.

J. Geophys. …, 2004

1] We report summertime measurements of CO and O 3 obtained during 2001-2003 at the PICO-NARE mountaintop station in the Azores. Frequent events of elevated CO mixing ratios were observed. On the basis of backward trajectories arriving in the free troposphere and global simulations of biomass burning plumes, we attribute nearly all these events to North American pollution outflow and long-range transport of biomass burning emissions. There was a high degree of interannual variability in CO levels: median [CO] ranged from 65 ppbv in 2001 to 104 ppbv in 2003. The highest concentrations were associated with transport of Siberian fire emissions during summer 2003, when Siberian fire activity was unusually high. Ozone mixing ratios also increased (by up to $30 ppbv) during the fire events. These findings demonstrate the significant hemispheric scale impact that biomass burning events have on background CO and O 3 levels. O 3 enhancements of similar magnitude were also observed in North American pollution outflow. O 3 and CO were correlated during North American outflow events, with a slope averaging 1.0 (d[O 3 ]/d [CO], ppbv/ppbv) when no fire impact was present. This slope is more than 80% larger than early 1990s observations made in the eastern United States and nearshore outflow region, even after accounting for declining U.S. CO emissions and for CO loss during transport to the Azores, and is not consistent with simple dilution of U.S. outflow with marine background air. We conclude that a significantly larger amount of O 3 production occurred in the air sampled during this study, and we suggest several potential reasons for this, each of which could imply potentially significant shortcomings in current estimates of the hemispheric impact of North American emissions on tropospheric ozone and should be evaluated in future studies.

Atmospheric Chemistry and Physics Discussions, 2012

The objective of this study is to investigate the contribution of biomass burning in the formation of tropospheric O 3. Furthermore, the impact of biogenic emissions under fire and no fire conditions is examined. This is achieved by applying the CAMx chemistry transport model for a wild-land fire event over Western Russia (24 April-10 May 2006). The model results are compared with O 3 and isoprene observations from 117 and 9 stations of the EMEP network, respectively. Model computations show that the fire episode altered the O 3 sensitivity in the area. In particular, the fire emissions increased surface O 3 over Northern and Eastern Europe by up to 80 % (40-45 ppb). In case of adopting a high fire NO x /CO emission ratio (0.06), the area (Eastern Europe and Western Russia) is characterized by VOCsensitive O 3 production and the impact of biogenic emissions is proven significant, contributing up to 8 ppb. Under a lower ratio (0.025), total surface O 3 is almost doubled due to higher O 3 production at the fire spots and lower fires' NO emissions. In this case as well as in the absence of fires, the impact of biogenic emissions is almost negligible. Injection height of the fire emissions accounted for O 3 differences of the order of 10 %, both at surface and over the planetary boundary layer (PBL).

Journal of Geophysical Research, 2007

1] Carbon monoxide reached record high levels in the northern extratropics in the late summer and fall of 1998 as a result of anomalously large boreal fires in eastern Russia and North America. We investigated the effects of these fires on CO and tropospheric oxidants using a global chemical transport model (GEOS-Chem) and two independently derived inventories for the fire emissions that differ by a factor of two. We find that it is essential to use both surface and column observations of CO to constrain the magnitude of the fire emissions and their injection altitude. Our results show that the larger of the two inventories appears more reliable and that about half of the emissions were injected above the boundary layer. The boreal fire emissions cause a much larger enhancement in ozone when about half the emissions are released above the boundary layer than when they are released exclusively in the boundary layer, as a consequence of the role of PAN as a source of NO x as air descends in regions far from the fires. (2007), Impacts of enhanced biomass burning in the boreal forests in 1998 on tropospheric chemistry and the sensitivity of model results to the injection height of emissions,