K. Stebel

Pan‐Arctic enhancements of light absorbing aerosol concentrations due to North American boreal forest fires during summer 2004

[1]xa0During summer of 2004, about 2.7 million hectare of boreal forest burned in Alaska, the largest annual area burned on record, and another 3.1 million hectare burned in Canada. This study explores the impact of emissions from these fires on light absorbing aerosol concentration levels, aerosol optical depths (AOD), and albedo at the Arctic stations Barrow (Alaska), Alert (Canada), Summit (Greenland), and Zeppelin/Ny Alesund on Spitsbergen (Norway). The Lagrangian particle dispersion model FLEXPART was run backward from these sites to identify periods that were influenced by forest fire pollution plumes. It is shown that the fires led to enhanced values of particle light absorption coefficients (σap) at all of these sites. Barrow, about 1000 km away from the fires, was affected by several fire pollution plumes, one leading to spectacularly high 3-hour mean σap values of up to 32 Mm−1, more than the highest values measured in Arctic Haze. AOD measurements for a wavelength of 500 nm saturated but were estimated at above 4–5 units, unprecedented in the station records. Fire plumes were transported through the atmospheric column over Summit continuously for 2 months, during which all measured AOD values were enhanced, with maxima up to 0.4–0.5 units. Equivalent black carbon concentrations at the surface at Summit were up to 600 ng m−3 during two major episodes, and Alert saw at least one event with enhanced σap values. FLEXPART results show that Zeppelin was located in a relatively unaffected part of the Arctic. Nevertheless, there was a 4-day period with daily mean σap > 0.3 Mm−1, the strongest episode of the summer half year, and enhanced AOD values. Elevated concentrations of the highly source-specific compound levoglucosan positively confirmed that biomass burning was the source of the aerosols at Zeppelin. In summary, this paper shows that boreal forest fires can lead to elevated concentrations of light absorbing aerosols throughout the entire Arctic. Enhanced AOD values suggest a substantial impact of these plumes on radiation transmission in the Arctic atmosphere. During the passage of the largest fire plume, a pronounced drop of the albedo of the snow was observed at Summit. We suggest that this is due to the deposition of light absorbing particles on the snow, with further potentially important consequences for the Arctic radiation budget.

Aerosols in polar regions: A historical overview based on optical depth and in situ observations

Large sets of filtered actinometer, filtered pyrheliometer and Sun photometer measurements have been carried out over the past 30 years by various groups at different Arctic and Antarctic sites and ...

Remote sensing and inverse transport modeling of the Kasatochi eruption sulfur dioxide cloud

[1]xa0An analytical inversion method is used to estimate the vertical profile of sulfur dioxide (SO2) emissions from the major 2008 eruption of Kasatochi Volcano, located on the Aleutian Arc, Alaska. The method uses satellite-observed total SO2 columns from the Global Ozone Monitoring Experiment-2 (GOME-2), Ozone Monitoring Instrument (OMI), and Atmospheric InfraRed Sounder (AIRS) during the first 2 days after the eruption, and an atmospheric transport model, FLEXPART, to calculate the vertical emission profile. The inversion yields an emission profile with two large emission maxima near 7 km above sea level (asl) and around 12 km asl, with smaller emissions up to 20 km. The total mass of SO2 injected into the atmosphere by the eruption is estimated to 1.7 Tg, with ∼1 Tg reaching the stratosphere (above 10 km asl). The estimated vertical emission profile is robust against changes of the assumed eruption time, meteorological input data, and satellite data used. Using the vertical emission profile, a simulation of the transport extending for 1 month after the eruption is performed. The simulated cloud agrees very well with SO2 columns observed by GOME-2, OMI, and AIRS until 6 days after the eruption, and the altitudes agree with both Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observation measurements and ground-based lidar observations to within 1 km. The method is computationally very fast. It is therefore suitable for implementation within an operational environment, such as the Volcanic Ash Advisory Centers, to predict the threat posed by volcanic emissions for air traffic.

Characterization of Sub‐Arctic Aerosols at ALOMAR (69 N,16 E) using Sun Photometer Measurements (2002–2007)

The Atmospheric Optics Group (GOA‐UVA) at the University of Valladolid has carried out seven field campaigns to investigate Sub‐Arctic aerosols. The measurements have been made between 2002 and 2007 at the Arctic Lidar Observatory for Middle Atmosphere Research (ALOMAR), Ando/ya Rocket Range, Norway (69 N, 16 E, elev. 380 m) in order to investigate the main characteristics of the columnar aerosol properties in this area. Different sun photometers and spectroradiometers have been used for this purpose. The main systems have been sun photometer from Cimel. From the measurements we can retrieve the aerosol optical depth (AOD) and the derived Angstrom exponent (alpha) and provide information on pollution and Arctic haze events in the region. The optical properties are analyzed jointly with air mass back trajectories in order to investigate the prevailing aerosol types and determine the origin of the aerosols. Routine measurements carried out since 2006, in collaboration with NILU and ALOMAR, will provide bett...

An intercomparison campaign of ground-based UV-visible measurements of NO2, BrO, and OClO slant columns: Methods of analysis and results for NO2

[1] Within the framework of the Network for the Detection of Stratospheric Change (NDSC), an intercomparison campaign of ground-based zenith-sky viewing UV-visible spectrometers was held at the Andoya Rocket Range (69°N, 16°E) at Andenes, Norway, from February 12 to March 8, 2003. The chosen site is classified as a complementary NDSC site. Eight groups from seven countries participated in the campaign which focused on the measurements of slant columns of NO 2 , BrO, and OClO. This first campaign publication concentrates on measurements of the NO 2 slant columns. Different analysis criteria were investigated during the campaign. These included the use of fitting parameters as chosen by each group to provide what they considered to be optimized retrievals. Additional sets of parameters, imposed for all the groups, were also used, including the wavelength interval, absorption cross sections, and species fitted. Each instruments results were compared to the measurements of selected reference instruments, whose choice was based on a technique combining regression analysis and examination of the residuals with solar zenith angle. Considering the data obtained during the whole campaign for solar zenith angles between 75° and 95°, all instruments agreed within 5% in the case of NO 2 with imposed analysis parameters in the 425-450 nm region. Measurements agree less well when retrieving the NO 2 slant columns in the 400-418 nm region or when using parameters optimized by each investigator for their instrument.

An intercomparison campaign of ground-based UV-visible measurements of NO , BrO, and OClO slant columns: Methods of analysis and results for NO

[1] Within the framework of the Network for the Detection of Stratospheric Change (NDSC), an intercomparison campaign of ground-based zenith-sky viewing UV-visible spectrometers was held at the Andoya Rocket Range (69°N, 16°E) at Andenes, Norway, from February 12 to March 8, 2003. The chosen site is classified as a complementary NDSC site. Eight groups from seven countries participated in the campaign which focused on the measurements of slant columns of NO 2 , BrO, and OClO. This first campaign publication concentrates on measurements of the NO 2 slant columns. Different analysis criteria were investigated during the campaign. These included the use of fitting parameters as chosen by each group to provide what they considered to be optimized retrievals. Additional sets of parameters, imposed for all the groups, were also used, including the wavelength interval, absorption cross sections, and species fitted. Each instruments results were compared to the measurements of selected reference instruments, whose choice was based on a technique combining regression analysis and examination of the residuals with solar zenith angle. Considering the data obtained during the whole campaign for solar zenith angles between 75° and 95°, all instruments agreed within 5% in the case of NO 2 with imposed analysis parameters in the 425-450 nm region. Measurements agree less well when retrieving the NO 2 slant columns in the 400-418 nm region or when using parameters optimized by each investigator for their instrument.