Biomass burning in Siberia and Kazakhstan as an important source for haze over the Alaskan Arctic in April 2008
During ARCPAC (Aerosol, Radiation, and Cloud Processes affecting Arctic Climate) the airborne field experiment in April in northern Alaska, more than 50 biomass burning plumes were encountered. The measurements onboard the NOAA WP-3 aircraft and the Lagrangian transport model FLEXPART showed that the plumes were emitted by forest fires in the Lake Baikal area of Siberia and by agricultural burning in Kazakhstan and southern Russia. Emissions from the two fire types were chemically different with higher enhancement ratios relative to CO for most gas and aerosol species from the agricultural fires. These biomass burning emissions were the dominant contributor to the haze encountered in this area during April. In 2008, the fire season started earlier than usual in Siberia, which may have resulted in a more efficient transport of biomass burning emissions into the polar dome thereby further increasing the already strong influence of boreal forest fire emissions on Arctic Haze. Outside the fire plumes, typical values of CO, trace gases and aerosol were encountered for this time of year. FLEXPART compared quantitatively well to the measurements and therefore can be used to quantitatively determine the total amount of CO and other trace gases and aerosol injected into the Arctic from biomass burning and anthropogenic sources during the ARCPAC period.
Siberian and North American Biomass Burning Contributions to the Processes that Influenced the 2008 Arctic Aircraft and Satellite Field Campaigns
Current climate change scenarios predict increases in biomass burning in terms of increases in fire frequency, area burned, fire season length and fire season severity, particularly in boreal regions. Climate and weather control fire danger, which strongly influences the severity of fire events, and these in turn, feed back to the climate system through direct and indirect emissions, modifying cloud condensation nuclei and altering albedo (affecting the energy balance) through vegetative land cover change and deposition. Additionally, fire emissions adversely influence air quality and human health downwind of burning. The boreal zone is significant because this region stores the largest reservoir of terrestrial carbon, globally, and will experience climate change impacts earliest. Boreal biomass burning is an integral component to several of the primary goals of the ARCTAS (Arctic Research of the Composition of the Troposphere from Aircraft and Satellites) and ARCPAC (Aerosol, Radiation, and Cloud Processes affecting Arctic Climate) 2008 field campaigns, which include its implication for atmospheric composition and climate, aerosol radiative forcing, and chemical processes with a focus on ozone and aerosols. Both the spring and summer phases of ARCTAS and ARCPAC offered substantial opportunities for sampling fresh and aged biomass burning emissions. However, the extent to which spring biomass burning influenced arctic haze was unexpected, which could inform our knowledge of the formation of arctic haze and the early deposition of black carbon on the icy arctic surface. There is already evidence of increased extreme fire seasons that correlate with warming across the circumboreal zone. In this presentation, we discuss seasonal and annual fire activity and anomalies that relate to the ARCTAS and ARCPAC spring (April 1 - 20) and summer (June 18 - July 13) periods across Siberia and North America, with particular emphasis on fire danger and fire behavior as they relate to smoke emissions. Fire severity and subsequent emission levels are directly related to fire danger conditions, which reflect and incorporate both antecedent and current weather. In this century, it is predicted that fire regime increases will be the catalyst for ecosystem change, which will force ecosystems to move more rapidly towards a new equilibrium with climate. However, the reasons for ecosystem change are often accompanied by social and political drivers of land cover change, which complicate the relationship between fire and weather. For instance, since the collapse of the former Soviet Union, financial support for fire fighting is minimal, communal agricultural lands have been abandoned and a number of species are no longer protected (e.g. Saiga in Kalmykia), and each of these factors strongly influences vegetation cover and fire regimes, leading to a complicated interaction of processes that control fire and its affect on the larger environment.
Observation of a Major Biogenic Aerosol Growth Event in Rural Ontario: Correlation with Photochemical Activity and Comparison to Model Predictions
In the past few years there has been considerable attention given to the characterization of pollution events where large amounts of organic aerosol are observed. Aside from a study during Pacific 2001 (Shantz et al., 2004), there are few documented cases of significant organic aerosol growth events (i.e. many micrograms/m3) in biogenically impacted regions free from significant anthropogenic influence. In this talk, observations of such an event made at Egbert, Ontario in June 2007 will be presented. As part of a larger field campaign conducted by the University of Toronto and Environment Canada to measure the hygroscopic properties of the organic components of boundary layer particulates, organic aerosol was observed to rise to high levels (15 micrograms/cubic meter) during a multi-day period of sustained northerly flow with increasing temperature. Correlations with simultaneous gas phase measurements of VOCs, such as isoprene, monoterpenes, and their oxidation products, indicate that this was a photochemically-driven event. In particular, correlations with carbon monoxide amounts are distinctly different than during periods of urban outflow and biomass burning influence. The carbon monoxide formed during the event appears to be photochemically produced in amounts consistent with the Master Chemical Mechanism model predictions and the observed secondary organic aerosol amounts. Temporal comparison with predictions from a detailed regional climate model (AURAMS, Environment Canada) are excellent, indicating that the event occurred on a regional scale, driven by biogenic emissions from forests to the North. Simultaneous particle hygroscopicity measurements indicate that the biogenic organic aerosol was as least as active as that flowing from a highly polluted environment, i.e. from Southern Ontario and the US Midwest to the South. Overall, the biogenic aerosol arising from forest emissions will have important air quality and climate effects.
Evidence for Deposition of Black Carbon in the Springtime Arctic
Vertical profiles of black carbon (BC) mass were observed from the surface to almost 7-km altitude in April 2008 during flights from Fairbanks, Alaska using the NOAA Single-Particle Soot Photometer (SP2). In the free troposphere, the Arctic air mass was often influenced by long-range transport from biomass-burning and anthropogenic source regions at middle and high latitudes. BC mass loadings reached maximum values near 4-km altitude with mass loadings typical of those on the low end of values observed at midlatitude ground-based urban sites. In the boundary layer over the snow and ice north of Alaska, the air mass was largely decoupled from the advected pollution aloft. In this shallow layer, BC mass loadings increased with altitude from near the surface to the top of the boundary layer by up to a factor of five. Based on correlations with CO, this positive vertical gradient in BC is attributable to deposition of BC on snow or ice. The mechanism could be dry deposition on the ice and snow surface or involve precipitation with snow and ice particles. If dry deposition were the predominant removal process and assumptions were made about the timescales for mixing between the free troposphere and boundary layer, the observed BC profiles would constrain the deposition velocity of BC to the snow or ice. Understanding the removal of BC in the Arctic boundary layer is crucial for evaluating the impact of anthropogenic and natural sources of BC on Arctic climate.
Chemical Properties of Aerosols in the Central Arctic
The Arctic is extremely sensitive to climate change, yet ground-based measurements are limited due to the remoteness of the region. Aerosols affect climate either directly by scattering incoming solar radiation, or indirectly by acting as the seed upon which cloud droplets form. As such, changes in Arctic aerosol can have a significant impact on radiative forcing. However, the sources and processes that lead to these Arctic aerosols remain largely unknown. During the summer of 2008, aerosol properties were measured in the central Arctic Ocean aboard the Swedish icebreaker Oden as a part of the Arctic Summer Cloud and Ocean Study (ASCOS). The overall purpose of this International Polar Year project was to explore the effect of Arctic aerosols on cloud formation and ultimately the surface radiation budget. The specific goal of the work presented here is to determine the aerosol chemical composition in order to understand aerosol hygroscopicity. Results are compared to measurements made in the Canadian Arctic Archipelago aboard the Canadian Coast Guard Ship Amundsen as a part of the Surface Ocean Lower Atmosphere Study (SOLAS). Highly time-resolved aerosol chemical composition was measured using an Aerodyne time-of-flight aerosol mass spectrometer while aerosol size distributions were measured using a scanning mobility particle sizer. Preliminary analysis shows that a significant portion of the sub-micron non-refractory aerosol mass can be attributed to sulphate and a smaller portion to organics. These studies are one of the first to measure real- time aerosol chemical composition so far north and will contribute to our overall understanding of the sources, processes and chemistry of Arctic air.
Synoptic/Mesoscale Modulation of Cloud, Boundary-Layer, and Aerosol Processes During ASCOS/AMISA: Preliminary Results
Arctic clouds and boundary-layer processes are believed to have an important impact on the surface energy budget of the Arctic pack ice, and hence on the fate of the Arctic sea ice. The clouds and boundary-layer structure in turn are modulated by synoptic and mesoscale processes and by aerosols. Unfortunately, many of the complex interactive processes affecting key properties of the clouds and their effect on the sea ice are unknown. The overall objective of the Arctic Summer Cloud-Ocean Study (ASCOS) and Arctic Mechanisms of Interaction between the Surface and Atmosphere (AMISA) field program was to provide the data to improve our understanding of these processes during the fall freeze-up period. ASCOS/AMISA was conducted in August and September 2008 near the North Pole using coordinated measurements from the Swedish icebreaker Oden and the NASA DC-8 research aircraft. Both are IPY-approved projects. ASCOS measurements include an extensive array of ship-based and on-ice remote sensors, 4X daily rawinsondes, tethersonde measurements, helicopter-based measurements, and near-surface measurements. The measurements focused on the macro- and microphysical structure of the Arctic clouds, the associated high-temporal resolution thermal and kinematic structure of the lower troposphere, aerosol sizes and types, and the structure of the ice surface conditions. They utilize remote sensing technology combined with retrieval techniques and in-situ measurements. The remote sensing instruments include a Ka- band cloud radar, an enhanced S-band vertically-pointing cloud and precipitation radar, a ceilometer, a microwave radiometer, a 449 MHz wind profiler, a Doppler sodar, and a scanning 55-GHz radiometer. The DC- 8 measurements by AMISA provided in-situ and remote sensing observations of the microphysical structure of the clouds, the atmospheric thermodynamic structure, aerosol sizes and composition, and high resolution microwave and radiometric imagery of the sea ice. The airborne instruments included a cloud, aerosol, and precipitation spectrometer (CAPS); a volatile aerosol concentration and composition (VACC) system; a polarimetric scanning radiometer (PSR); dual-channel radiometers; and dropsondes. Four successful overflights of the Oden each provided 3-5 hours of on-station observations. This suite of measurements is one of the most complete ever obtained in the Arctic boundary layer over the pack ice. The presentation will summarize the data collected and the synoptic/mesoscale environment of the surface- based and airborne measurements. Preliminary multi-instrument analyses of interesting time periods will be used to illustrate the interaction between the synoptic/mesoscale structure and processes affecting the cloud microphysics; the Arctic boundary-layer; the aerosol amount, size and composition; and the surface energy fluxes. A brief discussion outlining how these data will be used to address the interdisciplinary objectives of ASCOS and AMISA will be given, focusing on the objectives linked to Arctic clouds.