摘要:

The Arctic Boundary Layer Expedition (ABLE 3A) used measurements from ground, aircraft, and satellite platforms to characterize the chemistry and dynamics of the lower atmosphere over Arctic and sub‐Arctic regions of North America during July and August 1988. The primary objectives of ABLE 3A were to investigate the magnitude and variability of methane emissions from the tundra ecosystem, and to elucidate factors controlling ozone production and destruction in the Arctic atmosphere. This paper reports the experimental design for ABLE 3A and a summary of results. Methane emissions from the tundra landscape varied widely from −2.1 to 426 mg CH4m−2d−1. Soil moisture and temperature were positively correlated with methane emission rates, indicating quantitative linkages between seasonal climate variability and soil metabolism. Enclosure flux measurement techniques, tower‐based eddy correlation, and airborne eddy correlation flux measurements all proved robust for application to methane studies in the tundra ecosystem. Measurements and photochemical modeling of factors involved in ozone production and destruction validated the hypothesized importance of low NOxconcentrations as a dominant factor in maintaining the pristine Arctic troposphere as an ozone sink. Stratospheric intrusions, long‐range transport of mid‐latitude pollution, forest fires, lightning, and aircraft are all potential sources of NOxand NOyto Arctic and sub‐Arctic regions. ABLE 3A results indicate that human activities may have already enhanced NOyinputs to the region to the extent that the lifetime of O3against photochemical loss may have already doubled. A doubling of NOxconcentration from present levels would lead to net photochemical production of O3during summer months in the Arctic (Jacob et al., this issue (a)). The ABLE 3A results indicate that atmospheric chemical changes in the northern high latitudes may serve as unique early warning indicators of the rates and magnitude of global envir

ISSN:0148-0227    

DOI:10.1029/91JD02109

年代:1992

数据来源: WILEY

摘要:

A meteorological overview of the Arctic Boundary Layer Expedition (ABLE 3A) flight series is presented. Synoptic analyses of mid‐tropospheric circulation patterns are combined with isentropic back trajectory calculations to describe the long‐range (400–3000 km) atmospheric transport mechanisms and pathways of air masses to the Arctic and sub‐Arctic regions of North America during July and August 1988. Siberia and the northern Pacific Ocean were found to be the two most likely source areas for 3‐day transport to the study areas in Alaska. Transport to the Barrow region was frequently influenced by polar vortices and associated short‐wave troughs over the Arctic Ocean, while the Bethel area was most often affected by lows migrating across the Bering Sea and the Gulf of Alaska, as well as ridges of high pressure which built into interior Alaska. July 1988 was warmer and dryer than normal over much of Alaska. As a result, the 1988 Alaska fire season was one of the most active of the past decade. Airborne lidar measurements verified the presence of biomass burning plumes on many flights, often trapped in thin subsidence layer temperature inversions. Several cases of stratosphere/troposphere exchange were noted, based upon potential vorticity analyses and aircraft lidar data, especially in the Barrow region and during transit flights to and

ISSN:0148-0227    

DOI:10.1029/91JD02640

年代:1992

数据来源: WILEY

摘要:

The budgets of O3, NOx(NO+NO2), reactive nitrogen (NOy), and acetic acid in the 0–6 km column over western Alaska in summer are examined by photochemical modeling of aircraft and ground‐based measurements from the Arctic Boundary Layer Expedition (ABLE 3A). It is found that concentrations of O3in the region are regulated mainly by input from the stratosphere, and losses of comparable magnitude from photochemistry and deposition. The concentrations of NOx(10–50 ppt) are sufficiently high to slow down O3photochemical loss appreciably relative to a NOx‐free atmosphere; if no NOxwere present, the lifetime of O3in the 0–6 km column would decrease from 46 to 26 days because of faster photochemical loss. The small amounts of NOxpresent in the Arctic troposphere have thus a major impact on the regional O3budget. Decomposition of peroxyacetyl nitrate (PAN) can account for most of the NOxbelow 4‐km altitude, but for only 20% at 6‐km altitude. Decomposition of other organic nitrates might supply the missing source of NOx. The lifetime of NOy, in the ABLE 3A flight region is estimated at 29 days, implying that organic nitrate precursors of NOxcould be supplied from distant sources including fossil fuel combustion at northern mid‐latitudes. Biomass fire plumes sampled during ABLE 3A were only marginally enriched in O3; this observation is attributed in part to low NOxemissions in the fires, and in part to rapid conversion of NOxto PAN promoted by low atmospheric temperatures. It appears that fires make little contribution to the regional O3budget. Only 30% of the acetic acid concentrations measured during ABLE 3A can be accounted for by reactions of CH3CO3with HO2and CH3O2. There remains a major unidentified source of acetic acid in

ISSN:0148-0227    

DOI:10.1029/91JD01968

年代:1992

数据来源: WILEY

摘要:

Measurements of ozone (O3) and aerosol distributions were made with an airborne lidar system in the Arctic and sub‐Arctic during July–August 1988 as part of the NASA Global Tropospheric Experiment/Arctic Boundary Layer Expedition (ABLE 3A). Aerosol and O3profiles were measured simultaneously above and below the Electra aircraft from near the surface to above the tropopause. In situ measurements of O3mixing ratios and aerosol size distributions and number densities were also made on the aircraft. Many different atmospheric conditions were investigated on long‐range survey flights in the Arctic and on intensive flights over the tundra, ice, and marine regions near Barrow and Bethel, Alaska. The tropospheric composition at high latitudes was found to be strongly influenced by stratospheric intrusions. Regions of low‐aerosol scattering and enhanced O3mixing ratios were correlated with descending air from the lower stratosphere. Over 37% of the troposphere along our flight track at latitudes>57°N had significantly enhanced O3levels due to stratospheric intrusions, and in the 4‐ to 6‐km altitude range the tropospheric extent of the enhanced O3exceeded 56%. Ozone mixing ratios of 80 ppbv at 6 km were common, with vertical O3gradients of over 11 ppbv km−1observed across the base of strong intrusions. In the mixed layer over the tundra, O3was in the 25–35 ppbv range with a gradient of 5.5 ppbv km−1, while in continental polar air masses, the average gradient in the lower troposphere was 7.4 ppbv km−1, indicating more downward transport of O3at higher latitudes. Due to the many forest fires that year, plumes from biomass burning sources were observed on several flights over Alaska. Plumes influenced about 10% of the air below 4 km, and in some photochemically active plumes, O3was enhanced by 10–20 ppbv over ambient levels. Pollution plumes from industrial sources were infrequently observed; however, a few large plumes were found over the North Pacific with greatly enhanced aerosol scattering and with O3le

ISSN:0148-0227    

DOI:10.1029/92JD00159

年代:1992

数据来源: WILEY

摘要:

NASA's Arctic Boundary Layer Expedition (ABLE 3A) conducted during the summer of 1988 focused on the distribution of trace species in the Alaskan Arctic troposphere (altitudes<7 km) and the relative importance of surface sources/sinks, local emissions, distant transport, and tropospheric/stratospheric exchange. In situ ozone and aerosol number density and size data obtained during aircraft flights from Point Barrow and Bethel, Alaska, are discussed. Data are also presented for the ferry flights between Wallops Island, Virginia, and Point Barrow, Alaska, via Thule, Greenland. The major source of summer ozone for the troposphere is the intrusion of stratospheric air and subsequent transport to the lower altitudes. Photochemistry of mixed layer emissions and ozone transported from high northern latitude urban/industrialized areas do not appear to play major roles as sources of ozone for the Alaska region. Ozone gradients reflect the loss at the surface and supply from the stratosphere. Free‐tropospheric ozone (3‐ to 7‐km altitude) averaged 74 ppbv compared to 32 ppbv for the mixed layer. All four mixed layers studied (water, wet tundra, dry tundra, and boreal forest) are net ozone sinks. Ozone loss mechanisms are a combination of the destruction via photochemistry, chemical reactions with surface emissions, and direct loss through deposition to the surface. The boreal forest is the most efficient of the ozone sinks. Aerosol data showed that, of the mixed layers studied, the boreal forest has the largest increase in aerosol number density relative to the free troposphere. With the exception of the boreal forest, a significant portion of mixed layer aerosols are from the free troposphere. Results also show that while, in theory, free‐tropospheric air can be classified as originating from continental or maritime regions (Siberia, Canada, Pacific Ocean, Gulf of Alaska), little difference was found in the ozone and fine aerosol number density composition of the air. This is attributed, in part, to modification of the air during transport from its source

ISSN:0148-0227    

DOI:10.1029/91JD01310

年代:1992

数据来源: WILEY

摘要:

Vertical turbulent fluxes of O3were measured by eddy correlation from a 12‐m high tower erected over mixed tundra terrain (dry upland tundra, wet meadow tundra, and small lakes) in western Alaska during the Arctic Boundary Layer Expedition (ABLE 3A). The measurements were made continuously for 30 days in July‐August 1988. The mean O3deposition flux was 1.3 × 1011molecules cm−2s−1. The mean O3deposition velocity was 0.24 cm s−1in the daytime and 0.12 cm s−1at night. The day‐to‐night difference in deposition velocity was driven by both atmospheric stability and surface reactivity. The mean surface resistance to O3deposition was 2.6 s cm−1in the daytime and 3.4 s cm−1at night. The relatively low surface resistance at night is attributed to light‐insensitive uptake of O3at dry upland tundra surfaces (mosses, lichens). The small day‐to‐night difference in surface resistance is attributed to additional stomatal uptake by wet meadow tundra plants in the daytime. Flux measurements from the ABLE 3A aircraft flying over the tower are in agreement with the tower data. The mean O3deposition flux to the world north of 60°N in July–August is estimated at 8.2 × 1010molecules cm−2s−1, comparable in magnitude to the O3photochemical loss rate in the region derived from the ABLE 3A aircraft data. Suppression of photochemical loss by small anthropogenic inputs of nitrogen oxides could have a major effect on O3concentrations in

ISSN:0148-0227    

DOI:10.1029/91JD02696

年代:1992

数据来源: WILEY

摘要:

Measurements of the reactive odd nitrogen compounds NO, NO2, peroxyacetyl nitrate (PAN), and NOyare presented for the summertime middle/lower troposphere (6.1–0.15 km) over northern high latitudes. In addition, the chemical signatures revealed from concurrent measurements of O3, CO, C2H2, C2H6, C3H8, C2Cl4, and H2O are used to further characterize factors affecting the budget and distribution of NxOy, in the Arctic and sub‐Arctic tropospheric air masses sampled over Alaska during the NASA Arctic Boundary Layer Expedition (ABLE 3A) field campaign. Many of the compounds listed above exhibited a general trend of median mixing ratios increasing in proportion with altitude within the lower 6‐km column. However, median mixing ratios of NO and NOx(NO + NO2) were nearly independent of altitude, having values of about 8.5 and 25 pptv, respectively. Median mixing ratios of NOyvaried from about 350 pptv within the lowest altitudes to about 600 pptv within the highest altitudes sampled. PAN constituted the largest fraction of NOy(∼50%) at the highest altitudes. In addition, PAN mixing ratios accounted for all of the approximate 60 pptv/km altitudinal dependency in NOy. The analyses presented implicate biomass burning in Siberia as the probable source of about one‐third of the NOyabundance within the middle/lower troposphere over Alaska. These analyses also implicate the downward transport of air from altitudes in the vicinity of the tropopause as a major contributor to the abundance of NOy, (∼30–50%) within the lower 6‐km column over Alaska. However, the exact origin of this high‐altitude NOyremains uncertain. The impact of lower latitude industrial/urban pollution also remains largely uncertain, although various chemical signatures imply inputs from these regions would have been relatively well

ISSN:0148-0227    

DOI:10.1029/92JD01491

年代:1992

数据来源: WILEY

摘要:

Aircraft measurements of peroxyacetyl nitrate (PAN) and other important reactive nitrogen species (NO, NO2, HNO3, peroxypropionyl nitrate (PPN), CH3ONO2, NOy) were performed at high latitudes over North America and Greenland during July–August 1988, at all altitudes between 0 and 6 km as part of an Arctic Boundary Layer Expedition (ABLE 3A). Complementing these were measurements of C1to C5hydrocarbons, O3, chemical tracers (C2Cl4, CO), and important meteorological parameters. PAN was found to be an important reactive nitrogen species in the free troposphere, with 95% of the mixing ratios falling in the range of 5 to 450 ppt. PAN increased systematically with height with mixing ratios of 100–700 ppt at 6 km and 0–50 ppt in the boundary layer. The free tropospheric PAN reservoir was present over the entire high‐latitude region sampled (50° to 82°N latitude and 60° to 160°W longitude). In the boundary layer, PAN mixing ratios were higher over land than over the North Pacific Ocean. Significant levels of PAN were measured within stratospheric intrusions, forest fire plumes, and episodes of remote pollution. Other organic nitrates such as PPN and CH3ONO2were found to be a small fraction of PAN (0–10%). PAN and O3were strongly correlated both in their fine and gross structures, and the latitudinal distribution of PAN in the free troposphere followed that of O3. A two dimensional global photochemical model is used to compare measurements and model results. Model simulations, correlations between reactive nitrogen species (e.g. PAN and NOy) and anthropogenic tracers (C2H2, CO, C2Cl4), and the composition of NOyitself support the view that the reactive nitrogen measured during ABLE 3 A is predominantly of anthropogenic origin with a minor stratospheric component. Transported industrial pollution, biomass burning, and the unique seasonal dynamics of the Arctic/sub‐Arctic region play a dominant role in defining this reactive nitrogen abundance. This PAN (and NOy) reservoir may contribute to the summertime maximum in deposited nitrate observed

ISSN:0148-0227    

DOI:10.1029/91JD00889

年代:1992

数据来源: WILEY

摘要:

Measurements of peroxyacetyl nitrate (PAN), NO, NO2, HNO3, NOy, (total odd nitrogen), and O3were made in the high‐latitude troposphere over North America and Greenland (35° to 82°N) during the Arctic Boundary Layer Expedition (ABLE 3A) (July–August 1988) throughout 0‐to 6‐km altitudes. These data are analyzed to quantitatively describe the relationships between various odd nitrogen species and assess their significance to global tropospheric chemistry. In the free troposphere, PAN was as much as 25 times more abundant than NOx. PAN to NOxratio increased with increasing altitude and latitude. PAN was found to be the single most abundant reactive nitrogen species in the free troposphere and constituted a major fraction of NOy, PAN to NOyratios were about 0.1 in the boundary layer and increased to 0.4 in the free troposphere. A 2‐D global photochemical model with C1‐C3hydrocarbon chemistry is used to compare model predictions with measured results. A sizable portion (≈50%) of the gaseous reactive nitrogen budget is unaccounted for, and unknown organic nitrates and pernitrates are expected to be present. Model calculations (August 1, 70°N) show that a major fraction of the observed NOx(50 to 70% of median) may find its source in the available PAN reservoir. PAN and the unknown reservoir species may have the potential to control virtually the entire NOxavailability of the high latitude troposphere. It is predicted that the summer NOxand O3mixing ratios in the Arctic/sub‐Arctic troposphere would be considerably lower in the absence of the ubiquitous PAN reservoir. Conversely, this PAN reservoir may be responsible for the observed temporal increase in tropospheric O

ISSN:0148-0227    

DOI:10.1029/91JD00890

年代:1992

数据来源: WILEY

摘要:

We report here the distribution of selected acidic gases and aerosol species in the North American Arctic and sub‐Arctic summer troposphere. The summertime troposphere is an acidic environment, with HCOOH and CH3COOH the principal acidic gases and acidic sulfate aerosols dominating the particulate phase. Our data show that the acidic gas and aerosol composition is uniform on a large spatial scale. There appears to be a surface source of NH4+over the Arctic Ocean pack ice which may reflect release of NH3from decay of dead marine organisms on the ice surface near ice leads, release from rotting sea ice, or an upward flux from surface ocean waters in open ice leads. This NH3appears to partially neutralize aerosol acidity in the boundary layer. Over sub‐Arctic tundra in southwestern Alaska inputs of marine biogenic sulfur from the nearby Bering Sea appear to be an important source of boundary layer aerosol SO42−. While there were only minor effects on aerosol chemistry over the tundra from sea salt, the rainwater chemistry showed influence from marine aerosols which were apparently incorporated into air masses during frontal passages moving inland from the Bering Sea. The rainwater acidity over the tundra (pH 4.69) is typical of remote regions. The principal acidity components are H2SO4and carboxylic acids, especially HCOOH. The carboxylic acids appear to have a strong continental biogenic source, but hydrocarbons of marine origin and emissions from forest fires may also be important. The wet deposition fluxes of NO3−‐N and SO42−‐S over sub‐Arctic tundra during July–August 1988 were 2.1 and 2.4 mmol m−2yr−1. Wet deposition of NO3−was nearly 3 times higher than the average NOydeposition flux, which is believed to represent primarily dry deposition of HNO3(Bakwin et al., this issue). Our measurements indicate that the mid‐troposphere in the Arctic is generally contaminated with low levels of anthropogenic pollutants even in summer when direct atmospheric coupling with mid‐latitude source regions was previously believed to be minimal. Stratospheric inputs may also be important as a source of Arctic tropospheric SO42−. On several occasions we sampled directly within plumes or highly contaminated air masses representing various anthropogenic sources. The composition of these pollution sources suggested that they were important in determining the large‐scale distribution of acidic gases and aerosol species in the Arctic summer troposphere. Outside the plumes the anthropogenic influences are chemically diffuse and variable, making it very difficult to quantitatively ascertain the magnitude of the effects. Present‐day “background” air during summertime in the North American Arctic and sub‐Arctic mid‐troposphere appears to have the following average composition (parts per trillion by volume): HCOOH (70), CH3COOH (70), HNO3(40), NO3−(10), SO42−(25), and NH4+(55). These concentrations which were observed on only a few isolated days can be compared to the grand average (Arctic and sub‐Arctic) mid‐tropospheric levels during July–August 1988: HCOOH (166 ± 81), CH3COOH (215 ± 90), HNO3(48 ± 29), NO3−(22 ± 17), SO42−(61 ± 30), and NH4+(68 ± 30). A “first‐look” comparison of the large‐scale mid‐tropospheric composition in a remote area of the northern hemisphere with that over a remote region of the southern hemisphere, the Amazon Basin, suggests no identifiable difference in the levels of NH4+but possibly twofold and fiv

ISSN:0148-0227    

DOI:10.1029/91JD00118

年代:1992

数据来源: WILEY