Bidleman T.F.,Umea University |
Bidleman T.F.,Environment Canada |
Jantunen L.M.,Environment Canada |
Hung H.,Environment Canada |
And 4 more authors.
Atmospheric Chemistry and Physics | Year: 2015
Air samples collected during 1994-2000 at the Canadian Arctic air monitoring station Alert (82°30' N, 62°20' W) were analysed by enantiospecific gas chromatography-mass spectrometry for I±-hexachlorocyclohexane (α-HCH), trans-chlordane (TC) and cis-chlordane (CC). Results were expressed as enantiomer fractions (EF Combining double low line peak areas of (+)/[(+) + (and±)] enantiomers), where EFs Combining double low line 0.5, < 0.5 and > 0.5 indicate racemic composition, and preferential depletion of (+) and (-) enantiomers, respectively. Long-term average EFs were close to racemic values for and α-HCH (0.504± 0.004, n = 197) and CC (0.505± 0.004, n=162), and deviated farther from racemic for TC (0.470 ± 0.013, n = 165). Digital filtration analysis revealed annual cycles of lower α-HCH EFs in summer-fall and higher EFs in winter-spring. These cycles suggest volatilization of partially degraded α-HCH with EF < 0.5 from open water and advection to Alert during the warm season, and background transport of α-HCH with EF > 0.5 during the cold season. The contribution of sea-volatilized α-HCH was only 11% at Alert, vs. 32% at Resolute Bay (74.68° N, 94.90° W) in 1999. EFs of TC also followed annual cycles of lower and higher values in the warm and cold seasons. These were in phase with low and high cycles of the TC/CC ratio (expressed as FTC Combining double low line TC/(TC+CC)), which suggests greater contribution of microbially "weathered" TC in summer-fall versus winter-spring. CC was closer to racemic than TC and displayed seasonal cycles only in 1997-1998. EF profiles are likely to change with rising contribution of secondary emission sources, weathering of residues in the environment, and loss of ice cover in the Arctic. Enantiomer-specific analysis could provide added forensic capability to air monitoring programs.
D'Amours R.,University of Alberta |
D'Amours R.,Canadian Meteorological Center |
Mintz R.,Environment Canada |
Mooney C.,Environment Canada |
Wiens B.J.,Environment Canada
Journal of Geophysical Research: Atmospheres | Year: 2013
This paper seeks to investigate the extent to which stratosphere-to- troposphere transport (STT) impacts the Canadian Rocky Mountain foothills. Beryllium-7 (7Be) was monitored weekly at Harlech, Alberta, from July 2003 to June 2004, and daily during the spring of 2004. These data, together with hourly ozone (O3) and relative humidity (RH) measurements, are presented and analyzed, with a focus on the spring of 2004. A Lagrangian dispersion model was used to help determine the origin of air parcels arriving at Harlech in order to assess if these periods were related to well-defined stratospheric intrusions. The modeling results show that events consisting of above average surface observations of 7Be and O3, and below average surface observations of RH, are the result of the arrival of air originating from the middle and upper troposphere. During the spring of 2004, no direct STTs were observed; all identified events were determined to be indirect STTs or middle to upper troposphere transport that occurred several days prior to being detected at Harlech. The most significant event occurred between 2 and 11 April, which had the longest period of elevated 7Be and O 3 observations and the lowest RH measured during the spring of 2004, and where the modeling showed a strong stratospheric input. This input can be connected with two well-defined stratospheric intrusions occurring over the northern Pacific Ocean, more than 5 days before the associated surface observations. Furthermore, the modeling shows that periods of below average 7Be and O3 occurred when the station was mainly influenced by air masses circulating in the boundary layer. Key Points 14-day inverse modeling for daily 7Be and O3 in Alberta, March-June 2004Only indirect stratospheric intrusions can be associated to high concentrationsLow concentrations are associated mainly to boundary layer air masses ©2013. American Geophysical Union. All Rights Reserved.
Mctaggart-Cowan R.,Environment Canada |
Girard C.,Environment Canada |
Plante A.,Canadian Meteorological Center |
Desgagne M.,Environment Canada
Monthly Weather Review | Year: 2011
The importance of stratospheric influences for medium-range numerical weather prediction (NWP) of the troposphere has led to increases in the heights of global model domains at operational centers around the world. Grids now routinely extend to 0.1 hPa (approximately 65 km) in these systems, thereby covering the full depth of the stratosphere and the lower portion of the mesosphere. Increasing the vertical extent of higher-resolution limited-area models (LAMs) nested within the global forecasts is problematic because of the computational cost of additional levels and the possibility of inaccuracy or instability in the high-speed stratospheric jets. An upper-boundary nesting (UBN) technique is developed that allows information from high-topped driving grids to influence the evolution of a lower-topped (;10 hPa) LAM integration in a manner analogous to the treatment of lateral boundary conditions. A stratospheric vortex displacement event in the winter of 2007 is used to study the effectiveness of the UBN technique. Tropospheric blocking over Europe leads to the development of an amplifying planetaryscale wave in the lower stratosphere that culminates in an anticyclonic wave break over Asia and a marked increase of wave-1 asymmetry. The rapid evolution of stratospheric potential vorticity (PV) is poorly represented in low-topped models, resulting in PV-induced forecast height errors throughout the depth of the troposphere on time scales as short as 2-5 days. Application of the UBN technique is shown to be an effective way for low-topped configurations to benefit from stratospheric predictability without the problems associated with the inclusion of the stratospheric flow in the higher-resolution model domain. The robustness and relative ease of implementation of the UBN technique may make this computationally inexpensive strategy attractive for a wide range of NWP applications. © 2011 American Meteorological Society.
Guffanti M.,U.S. Geological Survey |
Schneider D.J.,U.S. Geological Survey |
Wallace K.L.,U.S. Geological Survey |
Hall T.,National Weather Service - NWS |
And 2 more authors.
Journal of Geophysical Research: Atmospheres | Year: 2010
The extensive volcanic cloud from Kasatochi's 2008 eruption caused widespread disruptions to aviation operations along Pacific oceanic, Canadian, and U.S. air routes. Based on aviation hazard warnings issued by the National Oceanic and Atmospheric Administration, U.S. Geological Survey, the Federal Aviation Administration, and Meteorological Service of Canada, air carriers largely avoided the volcanic cloud over a 5 day period by route modifications and flight cancellations. Comparison of time coincident GOES thermal infrared (TIR) data for ash detection with Ozone Monitoring Instrument (OMI) ultraviolet data for SO2 detection shows congruent areas of ash and gas in the volcanic cloud in the 2 days following onset of ash production. After about 2.5 days, the area of SO2 detected by OMI was more extensive than the area of ash indicated by TIR data, indicating significant ash depletion by fall out had occurred. Pilot reports of visible haze at cruise altitudes over Canada and the northern United States suggested that SO2 gas had converted to sulfate aerosols. Uncertain about the hazard potential of the aging cloud, airlines coped by flying over, under, or around the observed haze layer. Samples from a nondamaging aircraft encounter with Kasatochi's nearly 3 day old cloud contained volcanic silicate particles, confirming that some fine ash is present in predominantly gas clouds. The aircraft's exposure to ash was insufficient to cause engine damage; however, slightly damaging encounters with volcanic clouds from eruptions of Reventador in 2002 and Hekla in 2000 indicate the possibility of lingering hazards associated with old and/or diffuse volcanic clouds. © 2010 by the American Geophysical Union.
Fromm M.,U.S. Navy |
Lindsey D.T.,National Oceanic and Atmospheric Administration |
Servranckx R.,Canadian Meteorological Center |
Yue G.,NASA |
And 4 more authors.
Bulletin of the American Meteorological Society | Year: 2010
An in-depth characterization of the seasonal occurrence of wildfire, pyroCb, and the resulting smoke plumes in North America is presented. The canonical model of LS aerosol is that the ultimate source/pathway for its material is the troposphere, and that material enters the LS by two primary irreversible mechanisms: slow cross-tropopause ascent in the tropics and rapid injection by volcanic eruptions. Aerosols, being a basic atmospheric constituent, are a fundamental tracer of polluting processes that affect both the troposphere and stratosphere. The day after a pyroCb was identified the absorbing aerosol index (AI) sensed by the Total Ozone Monitoring Spectrometer (TOMS) highlighted a smoke plume with peculiarly large AI values. Since the discovery of smoke in the stratosphere and the pyroCb, only a small number of individual case studies and modeling experiments have been performed.