Reconstruction of Northern Hemisphere 1950-2010 atmospheric non-methane hydrocarbons (original) (raw)
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Non-methane hydrocarbons in the Arctic atmosphere at Barrow, Alaska
Geophysical Research Letters, 1992
C2-C8 non-methane hydrocarbons (NMHCs) were detected in the arctic atmosphere at Barrow, Alaska, during seven sampling periods in March 1989. The most prominent NMHCs were ethene, acetylene, etha.ne, propane, and benzene. The concentrations and distribution of these species were similar to those observed at the same location in 1982 and in the Norwegian Arctic in 1983. The distribution of NMHCs in background arctic air during this period was similar to that of aged urban air. These findings provide additional evidence that NMHCs in the arctic atmosphere during spring may originate from industrialized mid-latitude regions and contribute to the arctic haze phenomenon. [Rasmussen et al., 1983; Hovet al., 1984; Blake and Rowland, !986]. Many of these species exhibit maximum concentrations during winter and declining levels during spring and summer [Rasmussen et al., 1983; Khalil and Rasmussen, 1984]. These profiles are similar to those exhibited by aerosol tracers of arctic haze [Rahn and McCaffrey, 1980]. Meteorological investigations indicate that sources of .arctic haze constituents are located in industrialized, mid-latitude regions [Miller, 1981]. Rahn [1981] has suggested that Eurasia may be a more important source than eastern Noah America. Hansen et al. [1989] observed that ratios of aerosol black carbon/CO2 in background arctic air during spring at Barrow, Alaska, were typical of coal or heavy fuel oil combustion in large installations, automobile exhaust, and domestic-scale natural gas combustion. NMHCs are also emitted from these sources. NMHC source profiles have been used in chemical mass balance (CMB) source reconciliation models to examine the origin of NMHCs in ambient air [Aronian et al., 1989]. Chemical alteration of NMHC source profiles during transport must be examined to apply CMB techniques in reconciling sources of NMHCs in background arctic air. The major atmospheric removal processes for NMHCs are gas phase oxidation by OH, nitrate radical (NO3), and ozone [Finlayson-Pitts and Pitts, !986]. The purpose of our investigation was to examine the origins of C2-C10 NMHCs in the springtime arctic atmosphere. Whole air samples were collected in Summa© polished stainless steel canisters on seven occasions during March 1989 at the National Oceanic and Atmospheric Administration's (NOAA) Geophysical Monitoring for Climatic Change (GMCC) observatory in Barrow, Alaska, and analyzed by a cryogenic preconcentration/high-resolution gas chromatography technique. The results of these analyses are discussed in light of the chemical reactivity of these e0rnpounds as they relate to the long-range transport of anthropogenic emissions from mid-latitude regions to the Arctic during early spring.
A 60 yr record of atmospheric carbon monoxide reconstructed from Greenland firn air
Atmospheric Chemistry and Physics, 2013
We present a reconstruction of the Northern Hemisphere (NH) high latitude atmospheric carbon monoxide (CO) mole fraction from Greenland firn air. Firn air samples were collected at three deep ice core sites in Greenland (NGRIP in 2001, Summit in 2006 and NEEM in 2008. CO records from the three sites agree well with each other 5 20 the rest by reaction with methane (CH 4 ) (e.g. . Changes in CO mole 18995 fraction ([CO]) can therefore impact numerous radiatively and chemically important atmospheric trace species, such as CH 4 , non-methane hydrocarbons (NMHCs) and hydrochlorofluorocarbons (HCFCs) by influencing OH concentrations (e.g. . Oxidation of CO by OH can also result in significant production of tropospheric ozone (e.g. .
Elementa: Science of the Anthropocene, 2015
A record spanning ten years of non-methane hydrocarbon (NMHC) data from the Pico Mountain Observatory (PMO), Pico Island, Azores, Portugal, was analyzed for seasonal NMHC behavior, atmospheric processing, and trends, focusing on ethane and propane. The location of this site in the central North Atlantic, at an elevation of 2225 m asl, allows these data to be used to investigate the background conditions and pollution transport events occurring in the lower free North Atlantic troposphere. The quantity ln([propane]/[ethane]) was used as an indicator of both photochemical processing and a marker for the occurrence of pollution transport events detected at the station. The Pico data were compared with three other continuous NMHC data sets from sites bordering the North Atlantic, i.e. the Global Atmospheric Watch (GAW) stations at Summit, Greenland, Hohenpeisssenberg, Germany, and Cape Verde, using ln([propane]/[ethane]) results as an indicator for the degree of photochemical processing ('aging') seen in the data. Comparisons of these three data sets showed some significant differences in the seasonal background and range of observed values. The statistical distribution of binned monthly data was determined, and individual sample events were then scaled to the monthly median observed value. Back trajectories, determined by the HYSPLIT model were used to investigate the geographic origin of the observed trace gases as a function of the degree of photochemical processing. Results show that PMO samples have been subjected to a diversity of air transport and aging, from highly processed air to freshly emitted air throughout the year, and in particular during summer months. The predominant air transport is from North America, with only occasional influence from continental areas located east and southeast (Europe and Africa). The available record was found to be too variable and still too short to allow deciphering NMHC trends from the data. Ethane and propane measurements at the PMO were compared with the MOZART-4 atmospheric chemistry and transport model at the appropriate time and location. The model was found to yield good agreement in the description of the lower range of atmospheric mole fractions observed, of the seasonal cycle, and the regional oxidation chemistry. However, ethane and propane enhancements in transport events were underestimated, indicating that after the ≥ 3 days of synoptic transport to PMO the spatial extent of plumes frequently is smaller than the 2.8° × 2.8° (∼300 km) model grid resolution.
Carbon monoxide and methane over Canada: July–August 1990
Journal of Geophysical Research, 1994
Carbon monoxide (CO) and methane (CH4) were measured in the 0.15-to 6-kin portion of the troposphere over subarctic and boreal landscapes of midcontinent and eastern Canada during July-August 1990. In the mid-continent region, Arctic air entering the region was characterized by relatively uniform CO concentrations (86-108 parts per billion by volume (ppbv)) and CH n concentrations (1729-1764 ppbv). Local biomass burning and long-range transport of CO into the area from industrial/urban sources and distant fires did frequently produce enhanced and variable concentrations. Emissions of CH n from the Hudson Bay lowlands was the primary source for enhanced and variable concentrations, especially at altitudes of 0.15-1 km. In eastern Canada, most of the observed variability in CO and CH n was similar in origin to the phenomena described for the midcontinent region. However, unexpectedly low concentrations of CO (51 ppbv) and CH 4 (1688 ppbv) were measured in the midtroposphere on several flights. Combined meteorological and chemical data indicated that the low CO-CH n events were the result of long-range transport of tropical Pacific marine air to subarctic latitudes. 1. INTRODUCTION This paper reports the results of a study of surface sources and atmospheric transport processes which influenced the spatial and temporal variability of tropospheric carbon monoxide (CO) and methane (CHn) over regions of central and eastern Canada during July-August 1990. The regions studied are some of the most remote areas remaining on the North American continent. We documented variable concentrations of both CO (50-466 parts per billion by volume (ppbv)) and CH n (1688-1841 ppbv) at altitudes of 0.15-6 kin, over relatively pristine subarctic and boreal landscapes. Meteorological factors and local surface emission sources explained most of the observed chemical variability. During summer months the polar front frequently retreats from these regions and is replaced by a complex interaction of air masses from northwesterly, westerly, and southwesterly to southerly directions. Inflow from the northwest transits several thousand kilometers of landscape (Alaska to north central Canada) with a high incidence of uncontrolled wildfires. Southerly flow to the Canadian Hudson Bay region has passed over regions of American industrial and urban emissions. We will show that the long-range transport of pollutants from these upwind continental sources, combined with emissions of CH n and CO from local wetlands and from local wildfires, produced the enhanced and variable concentra-•Institute for the Study of Earth, Oceans, and Space, University of New Hampshire, Durham.
Journal of Geophysical Research, 2003
1] We report measurements of light (C 2 -C 4 ) nonmethane hydrocarbons (NMHCs) and C 1 -C 4 alkyl nitrates made at Summit, Greenland, over a full annual cycle (June 1997(June -1998. The remoteness of the Summit camp from industrial source regions resulted in trends of these trace gases that showed a clear seasonal variation with low variability. Variability (calculated as the percentage 1-sigma deviation of a running 10-point mean) averaged 7-9% for ethane over the entire study. The shorter-lived species (ethyne, propane, and the butanes) exhibited variability from 12-20% in winter to 20-100% in summer. The best fit curve to the annual cycle of ethane is a sinusoidal oscillation, but each of the shorter-lived NMHCs exhibited flat periods of low concentrations during the summer months. The C 2 -C 4 NMHCs peaked between 8 and 24 February, with the longer-lived NMHCs maximizing latest. These data were broadly consistent with literature values, confirming that high-latitude Northern Hemisphere (NH) emissions are similar year to year. Employing their linear fall accumulation rates, we calculated average NMHC ratios versus ethane of 0.59(±0.10):0.33(±0.05):0.26(±0.08):0.14(±0.04) for propane, ethyne, n-butane, and ibutane, respectively. We suggest that these ratios represent useful quantities with which to compare averaged mid-and high-latitude NH emission ratios. We also report the first yearround observations of the seasonal cycle of light C 1 -C 4 alkyl nitrates. Similar to the NMHCs, the seasonal trend of these gases shows primary dependence on transport to Summit during winter, and photochemical removal during summer. Unlike their parent NMHCs, alkyl nitrate concentrations did not asymptote to low levels during summer and they exhibited winter maxima later with decreasing photochemical lifetime.
Carbon monoxide and methane in the North American Arctic and Subarctic troposphere: July–August 1988
Journal of Geophysical Research, 1992
Measurements of carbon monoxide (CO) and methane (CH4) were made in the North American Arctic during July-August 1988. The distribution of CH 4 was variable in the atmospheric mixed layer (0-2 km), with concentrations determined primarily by interactions of biogenic emissions from wet tundra and turbulent mixing processes. Carbon monoxide exhibited little variation in unpolluted mixed layer environments indicating a minor role for biogenic sources and/or sinks in determining its distribution. In the free troposphere (2-6 km) both CO and CH 4 were variable. Concentration gradients were most frequently associated with intrusions of upper tropospheric or stratospheric air into the midtroposphere, emissions from forest and tundra fires, and long-range transport of enhanced concentrations of these gases from unidentified sources. Summertime haze layers exhibited midtropospheric enhancements of CH 4 similar to those measured in winter Arctic haze events. However, these summer pollution episodes did not exhibit positive correlations with particulate sulfate. The summer Arctic and subarctic haze events observed during the Arctic Boundary Layer Expedition (ABLE 3) were primarily a result of forest and tundra fires of natural origin. The tendency for relatively high variability of CO and CH 4 at altitudes of 3-6 km indicates that ground-based monitoring will not provide an adequate assessment of the chemical composition of the Arctic troposphere to support future global change studies.
Journal of Geophysical Research, 2003
The Tropospheric Ozone Production about the Spring Equinox (TOPSE) experiment was designed to follow the role of photochemistry in the evolution of the springtime maximum of tropospheric ozone (O 3) in the Northern Hemisphere (NH) at high latitudes. Determination of the composition and seasonal evolution of volatile organic carbon (VOC) species, which take part in and are good indicators for photochemical processes in the troposphere, was an important part of this study. We report measurements of a large number of C 2-C 10 nonmethane hydrocarbons (NMHCs), selected C 1-C 2 halocarbons, and C 1-C 4 alkyl nitrates. These gases were quantified in whole air samples collected aboard the National Center for Atmospheric Research (NCAR) C-130 aircraft at altitudes between 30 m and 8 km. Seven TOPSE sampling trips were flown between early February and mid-May 2000 covering the region from Colorado (40°N) to Churchill (in Manitoba, Canada), Thule (in northern Greenland), and as far north as 85°N. These measurements represent the most comprehensive spatial characterization of the North American Arctic to date and revealed strong latitudinal, vertical, and temporal NMHC gradients. In the midtroposphere north of Churchill (58°N), AENMHCs decreased by 6.2ppbCbetweenFebruaryandMay(1.6ppbCmonthAˋ1)andthemagnitudeofthischangediminishedwithaltitude.Overthesameperiod,midtroposphericO3levelsincreasedby6.2 ppbC between February and May (1.6 ppbC month À1) and the magnitude of this change diminished with altitude. Over the same period, midtropospheric O 3 levels increased by 6.2ppbCbetweenFebruaryandMay(1.6ppbCmonthAˋ1)andthemagnitudeofthischangediminishedwithaltitude.Overthesameperiod,midtroposphericO3levelsincreasedby16 ppbv (4.2 ppbv month À1). Free tropospheric NMHC decreases were consistent with removal by hydroxyl (OH) radicals at an average mixing ratio for mid-March to mid-May of 4.1 Â 10 5 mol cm À3. The alkyl nitrates, which are a reservoir species for tropospheric reactive odd nitrogen (NO Y), revealed similar latitudinal, vertical, and temporal gradients to their parent NMHCs. Their total decreased by $4 pptv month À1 , representing 10% or less of NO Y. In conjunction with meteorological trajectory analysis, different trace gas signatures provided significant clues to the origins of individual polluted air masses. Several of these air masses were rapidly advected over the Pole from source regions in northeastern and western Europe as well as an air mass that originated over the southwestern United States/Baja California that contained unusually high levels of alkanes. In addition, episodes of low boundary layer (BL) O 3 associated with low NMHC mixing ratios and trajectories from over the Arctic Ocean were frequently sampled toward the latter part of the experiment. The TOPSE data described here provide a unique picture of NH trace gas evolution from winter to summer that will be invaluable to models investigating the role that anthropogenic emissions play in high latitude O 3 chemistry.
Arctic methane sources: Isotopic evidence for atmospheric inputs
2011
By comparison of the methane mixing ratio and the carbon isotope ratio (d 13 C CH4) in Arctic air with regional background, the incremental input of CH 4 in an air parcel and the source d 13 C CH4 signature can be determined. Using this technique the bulk Arctic CH 4 source signature of air arriving at Spitsbergen in late summer 2008 and 2009 was found to be −68‰, indicative of the dominance of a biogenic CH 4 source. This is close to the source signature of CH 4 emissions from boreal wetlands. In spring, when wetland was frozen, the CH 4 source signature was more enriched in 13 C at −53 ± 6‰ with air mass back trajectories indicating a large influence from gas field emissions in the Ob River region. Emissions of CH 4 to the water column from the seabed on the Spitsbergen continental slope are occurring but none has yet been detected reaching the atmosphere. The measurements illustrate the significance of wetland emissions. Potentially, these may respond quickly and powerfully to meteorological variations and to sustained climate warming.
Journal of Geophysical Research, 2006
Harvard Forest, a rural site located in central Massachusetts downwind of major urban-industrial centers, provides an excellent location to observe a typical regional mixture of anthropogenic trace gases. Air that arrives at Harvard Forest from the southwest is affected by emissions from the U.S. east coast urban corridor and may have residual influence from emissions in the upper Ohio Valley and Great Lakes region farther to the west. Because of its relatively long distance from large individual emission sources, pollution plumes reaching the site are a homogenized mixture of regional anthropogenic emissions. Concentrations of C 2-C 6 hydrocarbons along with CO and NO y were measured nearly continuously from August 1992 through July 1996 and from June 1999 through November 2001. By correlating observed concentrations to acetylene, which is almost solely produced during combustion, we are able to detect seasonal trends in relative emissions for this series of trace gases. Seasonal changes in n-butane and i-butane emissions may largely be influenced by different gasoline formulations in late spring and summer. Shifts in evaporation rates due to the annual temperature cycle could induce a seasonal pattern for n-pentane, i-pentane and n-hexane emissions. Emissions of ethane and propane lack clear seasonality relative to acetylene emissions and also correlate less with acetylene than other gases, indicating that emissions of these two gases are strongly influenced by sources not associated with fuel combustion. Changes in the observed correlations of CO 2 and CO relative to acetylene are consistent with published changes in the estimated emissions of CO 2 and CO over the past decade, though variability in the observations makes it difficult to precisely quantify these changes.