North American Tropospheric Ozone Sources During Summer 2008 ARCTAS/ARC-IONS Derived from Laminar Identification with Tracers and Fire Maps
The ARC-IONS (ARCTAS Intensive Ozonesonde Network Study;, coordinated ozonesonde network, following
the model of IONS-04 and IONS-06 [Thompson et al., 2007; 2008], operated over 17 Canadian and US sites in
2008, with daily launches (1-20 April; 26 June-12 July) during A-Train satellite overpasses, ~1300 local. The
summer phase of ARC-IONS supported ARCTAS (Arctic Research of the Composition of the Troposphere with
Aircraft and Satellites); sampling of ozone, CO and other tracers from ground bases and aircraft operating from
Yellowknife (NT) and Cold Lake (AB) in Canada. The laminar identification (LID; Thompson et al., 2008; Yorks
et al., 2009) method is applied to ozone and P-T-U profiles to determine ozone sources in the free troposphere.
In addition to stratospheric ozone and a mixture of regional pollution-convection-lightning, about half of free
tropospheric ozone is made up of recently advected ozone and background, aged ozone. Ensembles of back-
trajectories are combined with LID results and satellite maps to extract fire contributions to column ozone over
each ARC-IONS site. In addition, each sonde budget is disaggregated with respect to regional fire sources, eg
California, western Canada, eastern US. An upper limit of 25% pyrogenic ozone, on average, is obtained from
trajectory-fire coincidences over central and western Canada, with the "cleanest" site at Whitehorse (YK) and
the most fire-perturbed at Kelowna (BC) and Stonyplain (Edmonton). The fire fraction declines when likely
altitude of fire impacts is considered. Western North American sounding sites in 2008 were heavily affected by
US west coast and Siberian fires. Eastern Canadian and southern US fires were important sources of ozone
over Goose Bay, Egbert and maritime Canada.
Tropospheric Ozone Variability in the Arctic From Surface and Ozonesonde Observations
During 2008 a number of campaigns focused on Arctic atmospheric composition and the processes that control it. In conjunction with the Arctic Research of the Composition of the Troposphere from Aircraft and Satellite (ARCTAS) project a network of ozone profiling sites carried out near daily observations during April 2008 and June-July 2008 using balloon-borne ozonesondes as part of the Arctic Intensive Ozonesonde Network Study (ARCIONS). Many of these intensive measurements were done at locations with multi-year ozonesonde observations, providing an opportunity for comparison with the 2008 measurements. A notable difference in the spring of 2008 from the longer term observations was the paucity of boundary layer ozone depletion events at the Arctic Ocean coastal locations (Barrow, Resolute, Eureka). At Barrow, Alaska the 35- year record of surface ozone measurements showed that 2008 had the second lowest occurrence of these events both for the month of April and the spring season (March-April-May) as a whole. The possible meteorological conditions responsible for this year to year variability are investigated. In addition the spatial and temporal variability of tropospheric ozone over the Arctic and subarctic latitudes of North America are described based on both the intensive and longer-term ozonesonde observations.
Springtime Arctic Trace Gas Measurements and Comparisons With the Atmospheric Chemistry Experiment on SCISAT
The process of rapid stratospheric ozone loss in the polar regions begins during the polar winter, when dynamical and chemical conditions lead to the formation of reactive chlorine and bromine radicals. Arctic ozone loss varies significantly from year to year because of changing dynamical conditions. Therefore, long-term data sets of Arctic chemical composition measurements are needed to better understand the process of ozone loss, the links between ozone depletion and climate change, and the future evolution of ozone. Solar absorption spectra have been recorded at Eureka, Nunavut in the sunlit part of each year since July 2006, when a Bruker 125HR high-resolution Fourier transform infrared spectrometer was installed at the Polar Environment Atmospheric Research Laboratory (PEARL). Applying the optimal estimation technique, total columns and some vertical profile information are retrieved for a suite of trace gases that are involved in stratospheric ozone depletion. Total columns of O3, HCl, ClONO2, HNO3, and HF will be presented, with a focus on three Canadian Arctic ACE Validation spring campaigns that took place in 2007, 2008, and 2009. Very different dynamical situations were observed over Eureka during these three spring periods: the impact of these conditions on the trace gas measurements will be shown. SCISAT, also known as the Atmospheric Chemistry Experiment (ACE), is a Canadian satellite mission for remote sounding of the Earth's atmosphere and was launched on August 12, 2003. Its primary instrument is a high spectral resolution Fourier Transform Spectrometer (FTS) measuring sequences of atmospheric absorption spectra in solar occultation. From these spectra the vertical distribution of trace gases can be determined. Results of the Bruker 125HR comparisons with the ACE-FTS, made with the purpose of validating the satellite measurements, will be also shown.
ACE-FTS Satellite Observations of Ozone and Related Constituent Distributions in the Arctic: Highlights From 2008.
The Atmospheric Chemistry Experiment (ACE) is a Canadian satellite mission that was launched on-board the SCISAT platform in August 2003. The primary instrument for the ACE mission is a high-resolution (0.02 cm-1) infrared Fourier Transform Spectrometer (ACE-FTS) with a spectral range of 750-4400 cm- 1. This instrument makes solar-occultation measurements of over 30 different atmospheric trace gases with well-resolved vertical profiles from the upper troposphere to the lower thermosphere (under cloud-free conditions). Over 5 years of data have been collected since operational retrievals began in February 2004. The work shown here will expand upon the development of a trace-gas climatology based on the first five years of ACE-FTS observations that is currently being developed. Specifically, this study uses derived meteorological products to map the observations into equivalent latitude space and ultimately determine the variability of O3, HCl, ClONO2, HNO3, H2O, and ClO in the lower stratosphere. These observations are augmented with coincident measurements made by the Microwave Limb Sounder (MLS) on board the Aura satellite and with ground-based measurements made at the Polar Environment Atmospheric Research Laboratory (PEARL), a Network for the Detection of Atmospheric Composition Change (NDACC) site, in Eureka, Nunavut (80.05°N, 86.42°W). The results will focus on contrasting the observed distributions of trace gases in the Arctic in 2008 with those of the previous four years.
Evaluation of Aura/OMI Total Column Ozone and Tropospheric Ozone Residual Products using Ozonesonde Profiles from the ARCIONS Campaign
During the Arctic Intensive Ozonesonde Network Study (ARCIONS), a large number of sites located over the middle to high latitudes of North America launched daily ozonesondes in the spring (April) and summer (June/July) of 2008. We take advantage of the large number of launches at high northern latitudes to examine the retrieval accuracy of Aura's Ozone Monitoring Instrument (OMI) Total Column Ozone (TCO) and derived Tropospheric Ozone Residual (TOR) products with the equivalent integrated column amounts from ozonesondes with the SBUV/SAGE climatology add-on that estimates the ozone column amounts from the top of the sonde profile to the top of the atmosphere. We find that the OMI TCO and TOR tend to underestimate the sondes for all sites and both seasons. TCO differences between OMI and the sondes are found to be within 10%, while TOR-Sonde differences are observed to be as high as 50% at a number of sites, regardless of latitude and season. TCO amounts from OMI compared to those sonde sites located above 50N are found to be typically over 375 DU in April 2008 while June/July values are clustered around 300-350 DU. Below 50N, OMI-Sonde comparisons show less seasonal separation in total column ozone amounts. Comparisons between the TOR product and sonde integrated tropospheric column (ITC) show no apparent difference between spring and summer. Large differences in troposphere amounts occur even though tropopause heights compare to within just a few percent. Evaluation of the stratospheric column amounts between the ARCIONS sondes and Aura's Microwave Limb Sounder instrument may also be presented. Further investigation into a preliminary method of improving the TOR product using sondes as a validation source shows promise, particularly at high latitudes.
Exploitation of satellite data for assessing air quality over North America with a chemical transport model
We present results from the integration of data from different satellite instruments to assess North American surface ozone abundances in the GEOS-Chem model for August 2006. We assimilate observations of tropospheric ozone from the Tropospheric Emission Spectrometer (TES) with emissions of isoprene derived from formaldehyde data from the Ozone Monitoring Instrument (OMI) and emissions of NOx derived from NO2 data from the SCanning Imaging Absorption SpectroMeter for Atmospheric CHartographY (SCIAMACHY). In previous work we have shown that assimilation of the TES data provides an estimate of the contribution of background ozone to summertime surface ozone abundances over North America of 20-40 ppb. We quantify here the constraints on estimates of ozone production in the North American boundary layer provided by SCIAMACHY and OMI data. We also assess the impact of discrepancies in the description of vertical mixing in the boundary layer in the model on the simulated surface ozone abundances.
Defining The Tropopause Using High Resolution Sounding Data
It is common practice to define the vertical position of the tropopause given an atmospheric temperature profile. The standard World Meteorological Organization (WMO) definition of the tropopause was developed at a time when when atmospheric soundings had relatively low vertical resolution. In this study, we investigate the applicability of the WMO definition to radiosonde and aircraft data with high vertical resolution. The radiosonde data and aircraft soundings used are entirely from the mid-latitudes of North America. Our results indicate that the WMO definition frequently underestimates tropopause heights by approximately 500 meters when using high-resolution temperature profiles. The underestimation is a result of the presence of thin stable layers in the upper troposphere that were not resolved in older sounding data. Modifications to the WMO definition and alternative methods are shown to significantly decrease observed underestimation.
Pan North-American Optical Effects of Kasatochi Volcanic Plume
The Kasatochi volcano (52.17 N, 175.51 W; 314 m above m.s.l) in the Aleutian island in Alaska unleashed a powerful eruption on August 7, 2008 as reported by the Alaska Volcano Observatory (http://avo.alaska.edu/activity/Kasatochi.php). Ground-based sun photometer measurements from AEROCAN / AERONET network stations, along with remote sensing imagery products (CALIPSO, MODIS, OMI) and Back trajectories (HYSPLIT model) was used to analyze, map and track the volcanic plume. Calipso and ground- based lidar profiles of attenuated backscatter and depolarization ratio over North America show that the volcanic plume was present over a significant portion of the upper troposphere and lower stratosphere.