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Title: Ten-year chemical signatures associated with long-range transport observed in the free troposphere over the central North Atlantic

Ten-year observations of trace gases at Pico Mountain Observatory (PMO), a free troposphere site in the central North Atlantic, were classified by transport patterns using the Lagrangian particle dispersion model, FLEXPART. The classification enabled identifying trace gas mixing ratios associated with background air and long- range transport of continental emissions, which were defined as chemical signatures. Comparison between the chemical signatures revealed the impacts of natural and anthropogenic sources, as well as chemical and physical processes during long transport, on air composition in the remote North Atlantic. Transport of North American anthropogenic emissions (NA-Anthro) and summertime wildfire plumes (Fire) significantly enhanced CO and O 3 at PMO. Summertime CO enhancements caused by NA-Anthro were found to have been decreasing by a rate of 0.67 ± 0.60 ppbv/year in the ten-year period, due possibly to reduction of emissions in North America. Downward mixing from the upper troposphere and stratosphere due to the persistent Azores-Bermuda anticyclone causes enhanced O 3 and nitrogen oxides. The d [O 3]/d [CO] value was used to investigate O 3 sources and chemistry in different transport patterns. The transport pattern affected by Fire had the lowest d [O 3]/d [CO], which was likely due to intense COmore » production and depressed O 3 production in wildfire plumes. Slightly enhanced O 3 and d [O 3]/d [CO] were found in the background air, suggesting that weak downward mixing from the upper troposphere is common at PMO. Enhancements of both butane isomers were found during upslope flow periods, indicating contributions from local sources. The consistent ratio of butane isomers associated with the background air and NA-anthro implies no clear difference in the oxidation rates of the butane isomers during long transport. Based on observed relationships between non-methane hydrocarbons, the averaged photochemical age of the air masses at PMO was estimated to be 11 ± 4 days.« less
Authors:
 [1] ;  [2] ;  [3] ;  [4] ;  [5] ;  [6] ;  [3] ;  [3]
  1. Michigan Technological Univ., Houghton, MI (United States). Atmospheric Sciences; National Inst. of Aerospace, Hampton, VA (United States)
  2. Michigan Technological Univ., Houghton, MI (United States). Atmospheric Sciences; Environmental Protection Agency (EPA), Research Triangle Park, NC (United States)
  3. Michigan Technological Univ., Houghton, MI (United States). Atmospheric Sciences
  4. Univ. of Colorado, Boulder, CO (United States). Inst. of Arctic and Alpine Research
  5. Univ. of Sheffield (United Kingdom). Chemical and Biological Engineering
  6. Michigan Technological Univ., Houghton, MI (United States). Atmospheric Sciences; Univ. of Birmingham (United Kingdom)
Publication Date:
Grant/Contract Number:
SC0006941; ATM-0720955; AGS-1110059
Type:
Accepted Manuscript
Journal Name:
Elementa
Additional Journal Information:
Journal Volume: 5; Journal ID: ISSN 2325-1026
Publisher:
University of California Press
Research Org:
Michigan Technological Univ., Houghton, MI (United States)
Sponsoring Org:
USDOE Office of Science (SC), Biological and Environmental Research (BER) (SC-23); National Science Foundation (NSF)
Country of Publication:
United States
Language:
English
Subject:
54 ENVIRONMENTAL SCIENCES; long-range transport patterns to Azores; long-term observations of ozone and ozone precursors; non-methane hydrocarbon aging
OSTI Identifier:
1425464