Flask Air Samples Research Articles

Regional CO2 fluxes inferred from mixing ratio measurements: estimates from flask air samples in central Kansas, USA

We estimated regional fluxes of carbon dioxide (CO2) using mixing ratios measured in a tallgrass prairie in central Kansas, USA over 3 yr (2002–2004). Glass flasks were used to collect whole air samples in the midafternoon for determining CO2 mixing ratios and their carbon isotopic composition. Regional CO2 fluxes were calculated assuming atmospheric boundary layer (ABL) approaches an equilibrium state on a monthly basis. CO2 mixing ratios derived from the marine boundary layer data were used as a proxy to represent those in the free troposphere, which allowed for determining a boundary layer CO2 gradient primarily resulting from surface exchange.We estimated temporal changes in the ABL height for this region on a monthly basis (600–1700 m asl for a 5-yr average between 1997 and 2001) from European Center for Medium-Range Weather Forecasts (ECMWF) model data. Accordingly, we estimated the rate of entrainment (flux density) by interpolating NCAR/NCEP reanalysis data to the estimated ABL height. Our study differentiates from previous studies in several aspects: (1) we used flask-based mixing ratio measurements; (2) only discrete midday CO2 mixing ratio data were used to construct weekly CO2 gradients between free troposphere and the ABL and (3) we propose a new means for estimating monthly values of vertical transport. Modelled regional CO2 fluxes were compared to net ecosystem exchange (NEE) of CO2 fluxes measured by eddy covariance method. Assuming negligible verticalCO2 gradients between mid-ABL and the surface layer and with no correction applied, calculatedNEE showed a general agreement with measured NEE fluxes throughout the growing season. Using CO mixing ratio data, we show that fossil fuel burning contributed negligible CO2 fluxes in summer but partially explained the discrepancy between modelled regional CO2 fluxes and measured NEE in winter. This wintertime fossil fuel input was consistent with carbon isotope measurements of CO2.We demonstrate in this study that CO2 mixing ratios subsampled at midday in the surface layer can be used to gain insights into regional CO2 flux exchange in the U.S. Great Plains area.

Trends in methane and sulfur hexafluoride at a tropical coastal site, Thumba (8.6°N, 77.°E), in India

Measurements of methane (CH 4 ) and sulfur hexafluoride (SF 6 ) have been made using gas chromatographic technique at a coastal site, Thumba (8.6°N, 77°E), India from the flask air samples collected during 1996–2000. The growth rates of CH 4 and SF 6 are observed to be 30 and 0.25 pptv yr −1 respectively. The growth rate of CH 4 at Thumba is found to be much higher than its average growth rate of about 7 ppbv yr −1 at other tropical monitoring sites. The observed growth rate of SF 6 at Thumba is similar to that found at other tropical stations. Seasonal amplitudes in CH 4 and SF 6 are higher at Thumba when compared to the other sites. The large growth rate of CH 4 at Thumba could be attributed to the increase in regional sources, and the greater seasonal amplitude is shown to be caused by the change in dynamical structure from Northern Hemisphere summer to winter.

The impact of local winds and long-range transport on the continuous carbon dioxide record at Mount Waliguan, China

This paper describes the continuous measurements of atmospheric carbon dioxide at Mt. Waliguan (36°17ʹN, 100°54ʹE, 3816 m asl) in western China over the period 1994–2000. The CO2 hourly mixing ratios were segregated by horizontal wind direction/speed and vertical winds, respectively, merged by season over the entire measurement period. The short-term variability in CO2 was examined mainly from the point of view of local winds observed at this station and isobaric back trajectory cluster-concentration analysis as for local and long-range transport influence, to permit the selection of hourly average data that is representative of background conditions. From the selected hourly data, daily, monthly and annual averages that are not influenced by local CO2 sources and sinks be computed by discriminating the local and regional impact on the Waliguan CO2 records. On the basis of these results, background CO2 data were then analyzed to evaluate the averaged diurnal variation, monthly mean time series, CO2 mixing ratio distribution in different seasons as well as averaged seasonal cycle. Annual mean and growth rate of CO2 at Waliguan during the period of 1991 to 2000 were further discussed by supplement with NOAA/CMDL flask air sampling records at this station and other monitoring stations located at similar latitudinal band in the Northern Hemisphere. The results from this study can provide atmospheric CO2 characteristics in Asian inland regions, and be used in other studies to improve the understanding of carbon source and sink distributions.

The impact of local winds and long-range transport on the continuous carbon dioxide record at Mount Waliguan, China

This paper describes the continuous measurements of atmospheric carbon dioxide at Mt. Waliguan (36°17ʹN, 100°54ʹE, 3816 m asl) in western China over the period 1994–2000. The CO2 hourly mixing ratios were segregated by horizontal wind direction/speed and vertical winds, respectively, merged by season over the entire measurement period. The short-term variability in CO2 was examined mainly from the point of view of local winds observed at this station and isobaric back trajectory cluster-concentration analysis as for local and long-range transport influence, to permit the selection of hourly average data that is representative of background conditions. From the selected hourly data, daily, monthly and annual averages that are not influenced by local CO2 sources and sinks be computed by discriminating the local and regional impact on the Waliguan CO2 records. On the basis of these results, background CO2 data were then analyzed to evaluate the averaged diurnal variation, monthly mean time series, CO2 mixing ratio distribution in different seasons as well as averaged seasonal cycle. Annual mean and growth rate of CO2 at Waliguan during the period of 1991 to 2000 were further discussed by supplement with NOAA/CMDL flask air sampling records at this station and other monitoring stations located at similar latitudinal band in the Northern Hemisphere. The results from this study can provide atmospheric CO2 characteristics in Asian inland regions, and be used in other studies to improve the understanding of carbon source and sink distributions.

Interannual growth rate variations of atmospheric CO2 and its δ13C, H2, CH4, and CO between 1992 and 1999 linked to biomass burning

High‐precision, multispecies measurements of flask air samples since 1992 from CSIRO's global sampling network reveal strong correlation among interannual growth rate variations of CO2 and its δ13C, H2, CH4, and CO. We show that a major fraction of the variability is consistent with two emission pulses coinciding with large biomass burning events in 1994/1995 and 1997/1998 in tropical and boreal regions, and observations of unusually high levels of combustion products in the overlying troposphere at these times. Implied pulse strengths and multispecies emission ratios are not consistent with any other single process, but do not exclude possible contributions from covarying processes that are linked through climatic forcing. Comparison of CO2 with its δ13C indicates that most of the CO2 variation is from terrestrial exchange, but does not distinguish forcing by biomass burning from imbalance in photosynthesis/respiration of terrestrial ecosystems. Partitioning of terrestrial CO2 fluxes is constrained by H2, CH4, and CO, all of which are products of biomass burning but which have no direct link to net respiration of CO2. While CO is a strong indicator of biomass burning, its short lifetime prevents it from usefully constraining the magnitude of CO2 emissions. If the H2 and CH4 variations were dominated by biomass burning, they would imply associated carbon emissions in excess of mean annual levels of other years, of 0.6–3.5 and 0.8–3.7 Pg C for 1994/1995 and 1997/1998, respectively. The large range in emission estimates mainly reflects uncertainty in H2/CO2 and CH4/CO2 emission ratios of fires in these years.

Atmospheric CO2 concentrations and δ13C measurements along a hemispheric course (1998/99, Italy to Antarctica)

Continuous measurements of atmospheric CO2 concentrations were carried out along three ship-routes from Italy to Antarctica in 1994/95, 1996/97 and 1998/99. The growth rate of CO2 for four latitudinal belts with arbitrarily chosen boundaries (from 45°N to 80°S) is reported for the three expeditions. The northernmost belt shows the largest growth rate between 1996 and 1998 (close to 6 ppm/yr) while southern belts show an almost constant growth rate of 1.7 ppm/yr. Anthropogenic activities clearly affect both CO2 concentrations and growth rates. δ13C measurements were carried out on CO2 from 23 flask air samples collected during the 1998/99 expedition. Apart from negative values observed in highly polluted areas, a negative trend is observed across the Antarctic Convergence Area with no changes in the atmospheric concentration of CO2. The hypothesis of a biochemical origin of these light carbon isotope values is suggested.

Analysis System for Measurement of CO2Mixing Ratios in Flask Air Samples

A system for measuring the concentration of CO2 in flask air samples from the NOAA/CMDL worldwide flask sampling network is described. Up to 180 samples per day can he analyzed using a nondispersive infrared CO2 analyzer. All data acquisition and instrument control operations are handled by a Hewlett-Packard Series 300 desktop computer. A noncontaminating diaphragm pump transfers the sample from the flask to the NDIR CO2 analyzer. Tests conducted using flasks filled from tanks of dry air showed either no systematic offsets or a small offset of about 0.1 ppm. The precision of the analysis system is estimated to be better than 0.1 ppm.

Carbon isotope dynamics of free-air CO2-enriched cotton and soils

A role for soils as global carbon sink or source under increasing atmospheric CO2 concentrations has been speculative. Free-air carbon dioxide enrichment (FACE) experiments with cotton, conducted from 1989 to 1991 at the Maricopa Agricultural Center in Arizona, maintained circular plots at 550 μmol mol−1 CO2 with tank CO2 while adjacent ambient control plots averaged about 370 μmol mol−1 CO2. This provided an exceptional test for entry of carbon into soils because the petrochemically derived tank CO2 used to enrich the air above the FACE plots was depleted in both radiocarbon (14C content was 0% modern carbon (pmC)) and 13C (δ13C≈ −36‰) relative to background air, thus serving as a potent isotopic tracer. Flask air samples, and plant and soil samples were collected in conjunction with the 1991 experiment. Most of the isotopic analyses on the plants were performed on the holocellulose component. Soil organic carbon was obtained by first removing carbonate with HCl, floating off plant fragments with a NaCl solution, and picking out remaining plant fragments under magnification. The δ13C of the air above the FACE plots was approximately −15 to −19‰, i.e. much more 13C depleted than the background air of approximately −7.5‰. The δ13C values of plants and soils in the FACE plots were 10–12‰ and 2‰13C-depleted, respectively, compared with their control counterparts. The 14C content of the FACE cotton plants was approximately 40 pmC lower than tha tof the control cotton, but the 14C results from soils were conflicting and therefore not as revealing as the δ13C of soils. Soil stable-carbon isotope patterns were consistent, and mass balance calculations indicate that about 10% of the present organic carbon content in the FACE soil derived from the 3 year FACE experiment. At a minimum, this is an important quantitative measure of carbon turnover, but the presence of 13C-depleted carbon, even in the recalcitrant 6 N HCl resistant soil organic fraction (average age 2200 years before present (BP)), suggests that at least some portion of this 10% is an actual increase in carbon accumulation. Similar isotopic studies on FACE experiments in different ecosystems could permit more definitive assessment of carbon turnover rates and perhaps provide insight into the extent to which soil organic matter can accommodate the ‘missing’ carbon in the global carbon cycle.

Airborne sampling of selected trace chemicals above the central United States

Field observations during a series of 24 atmospheric sampling flights in winter, spring, summer, and fall of 1987 provided a preliminary climatology of selected trace chemicals above the central United States. Flights were along the 91.5°W meridian between 29° and 41°N latitude. The data set includes continuous measurements of trace gases (O3, SO2, H2O2, and NO/NOy), aerosol number and size distributions, meteorological variables, and position. Filter samples produced SO42−, NO3−, SO2, and trace metal data. Flask air samples yielded methane, hydrocarbon (C2‐C5), and CO concentrations. Mean concentrations of the measured species at 2450±150 m and 1450±150 m represent each season. These data are discussed as functions of season, location, and air mass origin. Solar energy (821–991 w m−2), temperature (18°–11.6°C) and water vapor mixing ratio (13.5–10.1 g kg−1) peaked during summer at low and high altitude. Carbon monoxide levels 88–160 parts per billion by volume (ppbv) peaked in spring and were characteristic of the planetary boundary layer during both spring and summer. Methane concentrations were maximized during spring (1770–1744 ppbv) and fall (1774–1733 ppbv) and minimized during winter (1747–1730 ppbv) and summer (1736–1705 ppbv) at low and high altitude. Spring had the highest (21.3–21.4 ppbv) and summer the lowest (7.1–5.3 ppbv) hydrocarbon concentrations at low and high altitude. Sulfur dioxide concentrations were highest in summer (1.0–2.3 ppbv) and winter (0.9–1.6 ppbv) at low altitude. SO2 concentrations at high altitude had no seasonal trend and averaged less than 0.9 ppbv. Sulfate concentrations were highest in summer (3.2–1.7 μg m−3) at low and high altitude. The average hydrogen peroxide concentration varied by a factor of 16 (0.3–4.8 ppbv) between winter and summer. Ozone concentrations were between 49 and 70 ppbv and were highest in spring and summer. The ratio of sulfate to sulfur dioxide increased slightly with altitude during winter, spring, and summer. This is probably due to SO2 oxidation in clouds. The ratio of H2O2 to SO2 is >1 during spring and summer and <1 during winter. This indicates that the conversion of sulfur dioxide to sulfate by reaction with hydrogen peroxide is not oxidant‐limited during spring and summer.

Carbon dioxide and methane in the Arctic atmosphere

Fifty flask air samples were taken during April 1986 from a NOAA WP-3D Orion aircraft which flew missions across a broad region of the Arctic as part of the second Arctic Gas and Aerosol Sampling Program (AGASP II). The samples were subsequently analyzed for both carbon dioxide (CO2) and methane (CH4). The samples were taken in well-defined layers of Arctic haze, in the background troposphere where no haze was detected, and from near the surface to the lower stratosphere. Vertical profiles were specifically measured in the vicinity of Barrow, Alaska to enable comparisons with routine surface measurements made at the NOAA/GMCC observatory. Elevated levels of both methane and carbon dioxide were found in haze layers. For samples taken in the background troposphere we found negative vertical gradients (lower concentrations aloft) for both gases. For the entire data set (including samples collected in the haze layers) we found a strong positive correlation between the methane and carbon dioxide concentrations, with a linear regression slope of 17.5 ppb CH4/ppm CO2, a standard error of 0.6, and a correlation coefficient (r2) of 0.95. This correlation between the two gases seen in the aircraft samples was corroborated by in situ surface measurements of these gases made at the Barrow observatory during March and April 1986. We also find a similar relationship between methane and carbon dioxide measured concurrenty for a short period in the moderately polluted urban atmosphere of Boulder, Colorado. We suggest that the strong correlation between methane and carbon dioxide concentrations reflects a common source region for both, with subsequent long-range transport of the polluted air to the Arctic.

Airborne co 2 measurements in the Arctic during spring 1983

A set of flask air samples collected from aircraft in March and April 1983 during the Arctic Gas and Aerosol Sampling Program has been analyzed for CO 2 concentration. The results show CO 2 variations of several ppm in the Arctic troposphere, and qualitative agreement with measurements made on air samples collected at the surface. The CO 2 measurements together with air-mass characteristics determined during the flights show that CO 2 concentrations in the Arctic result from mixing of polluted air transported into the Arctic from lower latitudes with cleaner air of maritime and continental origins. The CO 2 concentration is found to increase or decrease with altitude which is probably dependent on the details of transport and the presence or absence of marine sources and/or sinks.