A13E-01
Global source identification of Arctic air pollution using statistical analysis of particle dispersion model output and measurement data
Arctic air pollution has received renewed interest recently because of its contribution to climate change in the Arctic. Nevertheless, its sources are still not known with sufficient accuracy. Most of our understanding of Arctic air pollution sources is based on model simulations, analysis of air pollution episodes or, at best, statistical analysis of air mass back-trajectories. Here, we present a new approach, namely combining the output of a Lagrangian particle dispersion model, FLEXPART, with measurement data from Arctic air pollution monitoring sites (Alert, Barrow, Summit, Zeppelin). This approach is similar to existing statistical methods for analyzing back-trajectories in conjunction with air pollution monitoring data. However, it has the advantage that the underlying model calculations also take into account turbulence and convection in the atmosphere, which are ignored by ordinary trajectory calculations. FLEXPART is run 20 days backward in time from each of the stations and every three hours, for several years. With every calculation, a so-called potential emission sensitivity (PES) field is obtained, which identifies where the measured air mass has come into contact with the Earth's surface. It quantitatively measures the sensitivity of the signal obtained at the station, to emissions occurring at or near the surface. By combining these PES fields with measured concentrations of several trace species e.g., carbon monoxide, sulphate, black carbon, and ozone. By performing a statistical analysis, we identify where the measured species most likely originate. Statistical analyses are performed both for average concentrations as well as the 10th and 90th percentiles of the measured frequency distribution. We implement a bootstrap resampling procedure to verify the statistical significance of the patterns observed in our retrieved PES maps. Some of our findings are: carbon monoxide and sulphate measured at Zeppelin originate from the Eurasian continent throughout the year. The statistical analysis even identifies specific source areas such as Norilsk/Murmansk/Moscow or the Black Sea region as well as from East Asia. For black carbon measured at Barrow, we also identify the Eurasian continent as the major source region during winter. However, during summer the highest black carbon concentrations arrive from Alaska and are presumably caused by boreal forest fires there. For ozone measured at Zeppelin, we find that titration by NO emissions causes the lowest ozone concentration in winter to arrive from Europe, whereas in summer photochemical ozone formation and transport from Europe causes the highest ozone concentrations. In spring (and partly in summer), air with the lowest ozone concentrations arrive from within the Arctic, likely indicating the importance of ozone depletion events.
A13E-02
Optical Properties and Climate Impacts of Tropospheric Aerosols that Undergo Long- Range Transport to the Arctic
Tropospheric aerosol particles undergo long range transport from the mid-latitudes to the Arctic each winter
and spring. Once in the Arctic, aerosols may impact the regional climate in several ways. Aerosols can affect
climate directly by scattering and absorbing incoming solar radiation and indirectly by acting as cloud
condensation nuclei and altering cloud properties. In addition, absorbing aerosol that is deposited onto ice
and snow can lower the surface albedo and enhance the ice-albedo feedback mechanism. Measurements of
aerosol properties relevant to climate forcing (chemical composition, light scattering, and light absorption)
have been made by NOAA at Barrow, AK for over a decade. In addition, in March and April of 2008, aerosol
measurements were made during a NOAA research cruise (ICEALOT) to the Greenland, Norwegian and
Barents Seas. Onboard the ship, measurements were made of aerosol optical and cloud nucleating
properties. Results from the long-term measurements and ICEALOT will be presented in order to describe
trends and climate-relevant properties of aerosol particles transported to the Arctic.
http://saga.pmel.noaa.gov/
A13E-03
Biomass burning in Siberia and Kazakhstan as the main source for Arctic Haze over the Alaskan Arctic in April 2008
During the airborne field experiment ARCPAC (Aerosol, Radiation, and Cloud Processes affecting Arctic Climate) in April in northern Alaska, more than 50 pollution plumes were encountered at altitudes between the surface and the highest flight level of 6.5 km. 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 Arctic 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. 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.
A13E-04
Analysis of Aerosol Characteristics Measured in the Arctic Atmosphere during ARCTAS
In situ measurements of aerosols were made on board the NASA DC-8 as part of the Arctic Research of the Composition of the Troposphere from Aircraft and Satellites (ARCTAS) campaign. A suite of aerosol instruments were installed on the DC-8 to measure the number concentrations, optical properties, and size distributions of aerosols and clouds. Flights were flown out of Fairbanks, Alaska during the spring of 2008 and out of Cold Lake, Canada during summer 2008. The spring flights measured instances of Arctic haze which result from the long range transport of pollution from mid-latitude source regions. We investigate the possible prevalence and radiative influence of ice clouds in these haze events. During the summer deployment, flights were flown to characterize emissions from Canadian forest fires. Both fresh and aged fire plumes were sampled in order to determine the impact of this source on the Arctic atmosphere. Aged Siberian and California forest fire plumes were also sampled. In this presentation, we document and contrast the microphysical and optical properties of aerosols from the different sources and examine how these properties change as a function of plume age and cloud processing.
A13E-05
Aerosol Chemical and Physical Properties Over an Ice-Free Region of the Arctic During the International Chemistry Experiment in the Arctic LOwer Troposphere (ICEALOT)
Atmospheric aerosol particles accumulate during the winter and spring in the Arctic resulting in a
phenomenon referred to as "Arctic Haze". Measurements of aerosol properties coupled with chemical
transport models are needed to understand changing trends in certain components of the "haze" as well as
the climatic impact of these aerosols. During March and April of 2008, an International Chemistry Experiment
in the Arctic Lower Troposphere (ICEALOT) was conducted aboard the R/V Knorr in the North Atlantic
Ocean and the Greenland, Norwegian, and Barents Seas from 41-80 degrees N. Here we report the
chemical and physical properties of the aerosol measured during the experiment. FLEXPART back
trajectories will be used to assess aerosol sources to the Arctic.
http://saga.pmel.noaa.gov/Field/icealot/index.html
A13E-06
Volatility-resolved Measurements of the Chemical Composition of Arctic Aerosol Particles
Here we describe measurements of the chemical composition of submicron particles in the Arctic marine boundary layer, taken on board the R/V Knorr during the IPY-ICEALOT mission (March-April 2008). Measurements were made with an Aerodyne high-resolution aerosol mass spectrometer (HR-AMS) for the measurement of the non-refractory fraction of the aerosol, in particular allowing for the determination of the oxygen/carbon (O/C) ratio of the particulate organics and the unambiguous identification of trace inorganic species. Sampling alternated between ambient air and air sent through a thermodenuder (TD), continually scanned between 50 and 250C in order to remove aerosol components by volatility. The mass spectra of particulate matter in the Arctic (including Arctic haze) were dominated by sulfur-containing peaks and the CO2+ ion (at m/z 44), indicating the main non-refractory components of the aerosol are acidic sulfate and highly oxygenated organics. Thermodenuder measurements allow for the clear speciation of sulfate compounds by volatility, as well as the comparison of the degree of atmospheric aging of the organics to measurements taken elsewhere (including at terrestrial sites). AMS measurements will be compared to results from a hygroscopicity tandem differential mobility analyzer (HTDMA), also downstream of the thermodenuder, as well as from semicontinuous (PILS) and offline (filter) measurements of particle composition.
A13E-07
Submicron Organic Aerosol Function Groups during the International Chemistry Experiment in the Arctic LOwer Troposphere (ICEALOT)
Aerosol organic mass (OM) components are expected to have significant direct and indirect impacts on Arctic climate, especially during springtime Arctic haze. The chemical and physical properties of OM in Arctic aerosol remain largely unconstrained. The R/V Knorr traveled between Iceland and the Barents Sea during the ice-free months of March and April of 2008 and collected submicron particles on teflon filters for Fourier Transform Infrared (FTIR) spectroscopy to identify and quantify organic functional groups. Time series and composition are presented along with air mass back trajectories to indicate source regions. Early findings identify alcohols, alkanes, and carboxylic acids, with smaller amounts of amines, aromatics, alkenes and carbonyls. These data show the important contributions of organic oxygen and nitrogen in the Arctic region. Single particle analysis by Near-edge X-ray Absorption Fine Structure (NEXAFS) Scanning Transmission X- ray Microscopy (STXM) provides additional information about the distribution and morphology of the types of organic particles. Comparison to collocated simultaneous measurements by other techniques showed good agreement for OM and oxygenated organic fractions.
A13E-08
Iceland Dust Storms Linked to Glacial Outwash Deposits and to Sub-Glacial Flood (Jökulhlaup) Events
Studies of Arctic snow and ice cores reveal large temporal changes in dust concentrations, especially over glacial-interglacial cycles. Most efforts to model dust variability with climate have focused on sources in tropical and mid-latitude arid regions and have neglected high latitude emissions because of a lack of information on possible sources. Here we report on aerosol measurements which show that dust storms are common on Iceland and that major events are associated with glacial sedimentary environments. In July 1991 we established an aerosol sampling site on Heimaey, a small island located 18 km off the southeast coast of Iceland, with the objective of studying the transport of pollutant species to the Arctic. We found that although concentrations of nitrate and non-sea-salt sulfate were generally quite low, there were sporadic peaks that were primarily attributed to pollutant transport from Europe [Prospero et al., 1995]. Recently we expanded our analyses to include mineral dust, covering the period 1997 through 2004. Dust is present during much of the year (annual average 3.9 μg m-3) with a strong seasonal cycle (maximum in April, 14.0 μg m-3). However there are many spikes in the dust record, some exceeding 100 μg m-3, which are not associated with pollutant transport peaks. A search of NASA satellite web archives yielded six "dust storm" images that were acquired during our data period. These show prominent dust plumes streaming off the coast of Iceland. Here we show that each image could be closely linked to a major dust peak in our record (although there were many more peaks than satellite images). Most of these dust events were associated with dust emitted from glacial outwash (sandur) deposits. Some of the largest dust peaks were linked to jökulhlaups, an Icelandic term for sub-glacially generated outburst floods. The dust clouds were typically comprised of a series of well-defined plumes emitted from large "point" sources, mostly associated with two major glaciers, Mýrdalsjökull and Vatnajökull, the latter being the largest glacier in Europe. In our presentation we review the Iceland dust aerosol data and show the relationship to these six satellite- captured dust outbreaks along with other environmental data associated with these events. We point out that the synoptic events associated with these dust outbreaks could carry dust into the high latitudes and to Europe. We also note that glaciers on Iceland have been retreating in recent decades and that this trend is expected to continue with changing climate. Thus dust activity from newly-exposed glacial deposits will most likely increase in the future on Iceland and possibly from other glacial terrains in the Arctic.