Abstract

Improvements made to an established mass spectrometric method for measuring changes in atmospheric O2/N2 are described. With the improvements in sample handling and analysis, sample throughput and analytical precision have both increased. Aliquots from duplicate flasks are repeatedly measured over a period of 2 weeks, with an overall standard error in each flask of 3–4 per meg, corresponding to 0.6–0.8 ppm O2 in air. Records of changes in O2/N2 from six global sampling stations (Barrow, American Samoa, Cape Grim, Amsterdam Island, Macquarie Island, and Syowa Station) are presented. Combined with measurements of CO2 from the same sample flasks, land and ocean carbon uptake were calculated from the three sampling stations with the longest records (Barrow, Samoa, and Cape Grim). From 1994–2002, We find the average CO2 uptake by the ocean and the land biosphere was 1.7 ± 0.5 and 1.0 ± 0.6 GtC yr?1 respectively; these numbers include a correction of 0.3 Gt C yr?1 due to secular outgassing of ocean O2. Interannual variability calculated from these data shows a strong land carbon source associated with the 1997–1998 El Niño event, supporting many previous studies indicating that high atmospheric growth rates observed during most El Niño events reflect diminished land uptake. Calculations of interannual variability in land and ocean uptake are probably confounded by non-zero annual air sea fluxes of O2. The origin of these fluxes is not yet understood.

Abstract

Atmospheric monitoring stations are operated at Barrow, Alaska; Mauna Loa, Hawaii; American Samoa; and South Pole by the Geophysical Monitoring for Climatic Change program to measure the characteristics of gaseous and aerosol species under background conditions. A nearly continuous record of light-scattering coefficient and condensation nuclei concentration measurements is available for Barrow since 1971, Mauna Loa since 1974, Samoa since 1977, and South Pole since 1974. The Barrow light-scattering data exhibit a strong annual cycle with a maximum in winter and spring (the Arctic haze) and a minimum in summer. The Barrow condensation nuclei data exhibit a strong semiannual cycle with a maximum coinciding with that of light scattering and an additional maximum about August. The Mauna Loa light-scattering data show a strong annual cycle with a maximum in April or May caused by long-range transport of Asian desert dust. The Mauna Loa condensation nuclei data show no significant annual cycle. The Samoa light-scattering and condensation nuclei data are representative of a clean marine atmosphere and exhibit no significant annual or diurnal cycle. The South Pole light-scattering data show a complicated annual cycle with a maximum in the austral summer and a minimum about April. The austral winter is dominated by events most likely caused by the transport of sea salt in the troposphere from the coastal regions to the interior of the Antarctic continent. The South Pole condensation nuclei data show a repeatable annual cycle with a maximum in the austral summer and a minimum in the austral winter. Linear least squares trend analyses show no significant trend compared to the standard error about the regression line at any station.

Abstract

An atmospheric monitoring station is operated at Cape Matatula, American Samoa, by the Geophysical Monitoring for Climatic Change program under the National Oceanic and Atmospheric Administration. A nearly continuous record of condensation nucleus (CN) concentration and multiwavelength aerosol scattering extinction coefficient (sp) is available from mid-1977 to the present. This report presents the 1977–1983 data. The long-term mean of CN concentration is 274 cm-3 the long-term mean of sp (550 nm) is 1.54×10-5, and no significant long-term, annual, or diurnal trend is apparent in either data record.

Abstract

Associations between the season-to-season changes in CO2 concentration and the sea-surface temperature in the eastern equatorial Pacific, the tropospheric air temperature, and the precipitation in the tropics are explored. The CO2 records at Mauna Loa and the South Pole from the Scripps Institution of Oceanography and the GMCC/NOAA program, as well as the GMCC records at Barrow, Alaska and American Samoa were used after the annual cycle and the growth due to fossil fuel emission has been removed. We find that the correlation between CO2 changes and each of the other variables changes with time. In particular, the period from about 1968 to about 1978 was the period of highest correlation, which was also the period when the climate variables were best correlated with each other. The air temperature and the precipitation were as well correlated with CO2 changes as was SST. Also, there are individual seasons when the CO2 changes are much better correlated with the climate variables than at other seasons. Furthermore, El Niño events, while the source of the largest signal in the CO2 record, are by no means the same from one event to the next. We take these results as further confirmation that the apparent effect of SST on the CO2 record comes less from changes in the equatorial eastern Pacific Ocean than from climate changes throughout the globe. Climate effects on the terrestrial biosphere seem a likely source of much of the interannual variation in atmospheric CO2.

Abstract

We use ozonesondes launched from Samoa (14 degrees S) during the Pacific Exploratory Mission (PEM) Tropics A to show that O-3 mixing ratios usually start increasing toward stratospheric values near 14 km. This is well below the tropical tropopause las defined either in terms of lapse rate or cold point), which usually occurs between 16 and 17 km. We argue that the main reason for this discrepancy in height between the chemopause and tropopause is that there is very little convective detrainment of ozone-depleted marine boundary layer air above 14 km. We conjecture that the top of the Hadley circulation occurs at roughly 14 km, that convective penetration above this altitude is rare, and that air that is injected above this height subsequently participates in a slow vertical ascent into the stratosphere. The observed dependence of ozone on potential temperature in the transitional zone between the 14-km chemopause and the tropical tropopause is consistent with what would be expected from this hypothesis given calculated clear-sky heating rates and typical in situ ozone production rates in this region. An observed anticorrelation between ozone and equivalent potential temperature below 14 km is consistent with what would be expected from an overturning Hadley circulation, with some transport of high O-3/low theta(e) air from midlatitudes. We also argue that the positive correlations between O-3 and N2O in the transitional zone obtained during the 1994 Airborne Southern Hemisphere Ozone Experiment/Measurements for Assessing the Effects of Stratospheric Aircraft) (ASHOE/MAESA) campaign support the notion that air in this region does have trace elements of Stratospheric air las conjectured previously), so that some of the ozone in the transitional zone does originate from the stratosphere rather than being entirely produced in situ.

Abstract

This report provides information on a potentially important new atmospheric tracer of large-scale behaviour at the Earth's surface, the oxygen isotope composition of CO2. We use measurements on flask air collected from Alaska, Hawaii, Samoa, Tasmania, coastal Antarctica and the South Pole. Recently, we examined 1982–84 measurements of 18O in CO2 extracted in situ from marine air at Cape Grim, Tasmania1. Here we report on a comparison of Cape Grim flask and in situ data that gives a measure of precision and serves to demonstrate a marked improvement over previous infrequent measurements. While previous data2,3 suggests a north-south gradient, our flask data establish a strong, asymmetric meridional gradient. We argue that this reflects the oxygen isotope ratio in ground water, via mechanisms involving gross catalysed CO2 exchange with leaf (and possibly soil) water. Very large CO2 fluxes are involved, of the order of 200 Gt carbon (C) yr-1.

Abstract

Variability in atmospheric CO2 concentration over periods of 1–5 days at Cape Matatula, American Samoa, was studied. The variability was found to be the result of the alternating influences of three air mass source regions. Partitioning of Samoa CO2 data according to these air mass source regions revealed annual cycles in the partitioned data sets corresponding to those of the tropical South Pacific, the mid-latitude southern hemisphere, and the tropical North Pacific regions.

Abstract

Ten years of isentropic trajectories were summarized using cluster analysis to describe flow patterns for American Samoa. The trajectories were then paired with surface ozone data to determine the dependence of surface ozone on transport. The two main transport regimes affecting surface ozone are trade wind transport, where trajectories show flow bringing ozone from the east in the tropical marine boundary layer, and midlatitude transport, where trajectories show strong westerly flow at higher elevations of southern midlatitudes, followed by descent with anticyclonic curvature. These two transport regimes yield ozone from distinctly different origins, having different mixing ratios. The seasonally changing frequency of transport type is shown to be partly responsible for the seasonal cycle and changes in variability of Samoa surface ozone. On average, 45% of winter ozone variation can be explained by differences in transport type. This strong relationship was absent, however, during 1991, probably because of UV blocking by aerosols from the eruption of Mount Pinatubo. Reduced total column ozone during winter 1992 may have contributed to this season having the lowest surface ozone levels of the study period.

Abstract

Ozone concentrations in the atmospheric boundary layer of the Pacific and Indian Oceans were measured on four separate oceanographic research cruises (July 1986, May to August 1987, April to May 1988). These measurements show a distinct zone of near zero (?3 ppb) ozone concentration in the central equatorial Pacific in April-May, with ozone increasing in this region over the next 4 months. The seasonal observed change in the latitudinal gradient of ozone is consistent with previous ozone measurements at Hilo and Samoa by Oltmans and Komhyr [1986] and predictions from an atmospheric general circulation model study [Levy et al., 1985]. A significant diurnal cycle of ozone was found in almost all locations with a maximum near sunrise, a minimum in the late afternoon, and a peak-to-peak amplitude of 1 to 2 ppb (10–20%), similar to that predicted by a photochemical model in the low NO x limit [Thompson and Lenschow, 1984].

Abstract

The primary goal of the third joint Soviet-American Gases and Aerosols (SAGA 3) experiment was to study trace gases and aerosols in the remote marine boundary layer. SAGA 3/leg 1 took place from February 13 to March 13, 1990, aboard the former Soviet R/V Akademik Korolev and consisted of five equatorial transects (designated transects 1 through 5) between 15°N and 10°S on a cruise track from HiIo, Hawaii, to Pago-Pago, American Samoa. Specific objectives were to study (1) the oceanic distribution and air-sea exchange of biogenic trace gases; (2) photochemical cycles of C-, S-, and N-containing gases in the marine boundary layer; (3) the distribution of aerosol particles in the marine boundary layer and their physical and chemical properties; (4) interhemispheric gradients and latitudinal mixing of trace gases and aerosols; and (5) stratospheric aerosol layers. SAGA 3/leg 2 continued from March 17 to April 7, 1990, with one more equatorial transect between American Samoa and the northern coast of the Philippines (transect 6) followed by a final transect to Singapore (transect 7). During leg 2, most former Soviet measurements continued, but with the exception of measurements of nitrous oxide (N2O) and selected halocarbons in the air and surface waters all American measurements ceased. This paper briefly summarizes the chemical measurements made by SAGA 3 investigators and presents in some detail the meteorological and hydrological characteristics encountered during SAGA 3. The meteorological analysis is based on atmospheric soundings of temperature, humidity, winds, sea surface temperature, postcruise back trajectories of winds, and satellite imagery. In general, the meteorology during SAGA 3 was typical of the location and time of year. Exceptions to this include an incipient El Niño that never developed fully, a poorly defined ITCZ on 4 of 6 equator crossings, wind speeds that were 20% greater than the decadal mean, a convective event that brought midtropospheric air to the surface (on Julian day 59), and transport of northern hemispheric air to 18°S during a synoptic scale tropical disturbance.

Abstract

A significant negative correlation exists between June-August sea surface temperatures (SSTs) in the eastern equatorial Pacific and 15-31 October total ozone values at South Pole, Antarctica. SSTs in the eastern equatorial Pacific were anomalously warmer by 0.67-degrees-C during 1976-1987 compared with 1962-1975. Quasi-biennial oscillation (QBO) easterly winds in the equatorial Pacific stratosphere were generally stronger after 1975 than they were before that time. Prior to the early-to-mid 1970s the trend in global ozone was generally upward, but then turned downward. Total ozone at Hawaii and Samoa, which had been decreasing at a rate of about 0.35% yr-1 during 1976-1987, showed recovery to mid-1970s values in 1988-1989 following a drop in SSTs in the eastern equatorial Pacific to low values last observed there prior to 1976. During 15-31 October 1988, total ozone at South Pole, which had decreased from about 280 Dobson units (DU) prior to 1980 to 140 DU in 1987, suddenly recovered to 250 DU, though substantial ozone depletion by heterogeneous photochemical processes involving polar stratospheric clouds was still evident in the South Pole ozone vertical profiles. These observations suggest that the downward trend in ozone observed over the globe in recent years may have been at least partially meteorologically induced, possibly through modulation by the warmer tropical Pacific ocean waters of QBO easterly winds at the equator, of planetary waves in the extratropics, of the interaction of QBO winds and planetary waves, and of Hadley Cell circulation. A cursory analysis of geostrophic wind flow around the Baffin Island low suggests a meteorological influence on the observed downward trend in ozone over North America during the past decade. Because ozone has a lifetime that varies from minutes to hours in the primary ozone production region at high altitudes in the tropical stratosphere to months and years in the low stratosphere, changes in atmospheric dynamics have the potential for not only redistributing ozone over the globe, but also changing global ozone abundance.

Abstract

An air sampling apparatus is described which standardizes sampling height at a field station at 10 m or more above ground level and which minimizes loss of particles and destruction and contamination of sampled trace atmospheric gases as air is conducted through the apparatus to various monitoring instruments. Basic design features render the apparatus useful for air sampling under widely varying climate conditions, and at station altitudes ranging from sea level to more than 4 km. Four systems have been built, and have been used sucessfully since 1977 at the NOAA Geophysical Monitoring for Climatic Change program baseline stations at Point Barrow, Alaska; Mauna Loa, Hawaii; American Samoa, South Pacific; and South Pole, Antarctica.

Abstract

Ozone trends, derived from 1979-1996 Dobson spectrophotometer total ozone data obtained at five U.S. mainland midlatitude stations, averaged -3.4, -4.9, -2.6, -1.9, and -3.3%/decade for winter, spring, summer, and autumn months, and on an annual basis, respectively. At the lower latitude stations of Mauna Loa and Samoa, corresponding-period annual ozone trends were -0.4 and -1.3%/decade, respectively, while at Huancayo, Peru, the 1979-1991 annual trend was -0.9%/decade. A linear trend approximation to ozone changes that occurred since 1978 during austral daylight times at Amundsen-Scott (South Pole) station, Antarctica, yielded a value of -12%/decade. By combining 1979-1996 annual trend data for three U.S. mainland stations with trends for the sites derived from 1963-1978 data, it is estimated that the ozone decrease at U.S. midlatitudes through 1996, relative to ozone present in the mid-1960s, was -6.7%. Similar analyses incorporating South Pole data obtained since 1963 yielded an ozone change at South Pole (daylight observations) through 1996 of approximately -25%. South Pole October total ozone values in 1996 were lower than mid-1960s October ozone values by a factor of two. Trend data are also presented for several shorter record period stations, including the foreign cooperative stations of Haute Provence, France; Lauder, New Zealand; and Perth, Australia.

Abstract

We present carbon dioxide (CO2) estimates from the Tropospheric Emission Spectrometer (TES) on the EOS-Aura satellite launched in 2004. For observations between 40° S and 45° N, we find about 1 degree of freedom with peak sensitivity at 511 hPa. The estimated error is ~10 ppm for a single target and 1.3–2.3 ppm for monthly averages on spatial scales of 20°×30°. Monthly spatially-averaged TES data from 2005–2008 processed with a uniform initial guess and prior are compared to CONTRAIL aircraft data over the Pacific ocean, aircraft data at the Southern Great Plains (SGP) ARM site in the southern US, and the Mauna Loa and Samoa surface stations. Comparisons to Mauna Loa data show a correlation of 0.92, a standard deviation of 1.3 ppm, a predicted error of 1.2 ppm, and a ~2% low bias, which is subsequently corrected. Comparisons to SGP aircraft data over land show a correlation of 0.67 and a standard deviation of 2.3 ppm. TES data between 40° S and 45° N for 2006–2007 are compared to surface flask data, GLOBALVIEW, the Atmospheric Infrared Sounder (AIRS), and CarbonTracker. Comparison to GLOBALVIEW-CO2 ocean surface sites shows a correlation of 0.60 which drops when TES is offset in latitude, longitude, or time. At these same locations, TES shows a 0.62 and 0.67 correlation to CarbonTracker at the surface and 5 km, respectively. We also conducted an observing system simulation experiment to assess the potential utility of the TES data for inverse modeling of CO2 fluxes. We find that if biases in the data and model are well characterized, the averaged data have the potential to provide sufficient information to significantly reduce uncertainty on annual estimates of regional CO2 sources and sinks. Averaged pseudo-data at 10°×10° reduced uncertainty in flux estimates by as much as 70% for some tropical regions.

Abstract

We describe the development of an automated gas chromatography-isotope ratio mass spectrometry (GC-IRMS) system capable of measuring the carbon isotopic composition of atmospheric methane (?13CH4) with a precision of better than 0.1‰. The system requires 200 mL of air and completes a single analysis in 15 min. The combination of small sample size, fast analysis time, and high precision has allowed us to measure background variations in atmospheric ?13CH4 through the NOAA Climate Monitoring and Diagnostics Laboratory Cooperative Air Sampling Network. We then present a record of ?13CH4 obtained from six surface sites of the network between January 1998 and December 1999. The sites are Barrow, Alaska (71°N); Niwot Ridge, Colorado (40°N); Mauna Loa, Hawaii (20°N); American Samoa (14°S); Cape Grim, Tasmania (41°S); and the South Pole (90°S). For the years 1998 and 1999, the globally averaged surface ?13C value was ?47.1‰, and the average difference between Barrow and the South Pole was 0.6‰. Consistent seasonal variations were seen only in the Northern Hemisphere, especially at Barrow, where the average amplitude was 0.5‰. Seasonal variations in 1998, however, were evident at all sites, the cause of which is unknown. We also use a two-box model to examine the extent to which annual average ?13C and CH4 mole fraction measurements can constrain broad categories of source emissions. We find that the biggest sources of error are not the atmospheric ?13C measurements but instead the radiocarbon-derived fossil fuel emission estimates, rate coefficients for methane destruction, and isotopic ratios of source emissions.

Abstract

Carbon monoxide (CO) mixing ratios were measured in air samples collected weekly at eight locations. The air was collected as part of the CMDL/NOAA cooperative flask sampling program (Climate Monitoring and Diagnostics Laboratory, formerly Geophysical Monitoring for Climatic Change, Air Resources Laboratory/National Oceanic and Atmospheric Administration) at Point Barrow, Alaska (71°N), Niwot Ridge, Colorado (40°N), Mauna Loa and Cape Kumakahi, Hawaii (19°N), Guam, Marianas Islands (13°N), Christmas Island (2°N), Ascension Island (8°S) and American Samoa (14°S). Half-liter or 3-L glass flasks fitted with glass piston stopcocks holding teflon O rings were used for sample collection. CO levels were determined within several weeks of collection using gas chromatography followed by mercuric oxide reduction detection, and mixing ratios were referenced against the CMDL/NOAA carbon monoxide standard scale. During the period of study (mid-1988 through December 1990) CO levels were greatest in the high latitudes of the northern hemisphere (mean mixing ratio from January 1989 to December 1990 at Point Barrow was approximately 154 ppb) and decreased towards the south (mean mixing ratio at Samoa over a similar period was 65 ppb). Mixing ratios varied seasonally, the amplitude of the seasonal cycle was greatest in the north and decreased to the south. Carbon monoxide levels were affected by both local and regional scale processes. The difference in CO levels between northern and southern latitudes also varied seasonally. The greatest difference in CO mixing ratios between Barrow and Samoa was observed during the northern winter (about 150 ppb). The smallest difference, 40 ppb, occurred during the austral winter. The annually averaged CO difference between 71°N and 14°S was approximately 90 ppb in both 1989 and 1990; the annually averaged interhemispheric gradient from 71°N to 41°S is estimated as approximately 95 ppb.

Abstract

Surface ozone measurements at the four baseline U.S. geophysical monitoring for climatic change observatories provide a glimpse of tropospheric ozone behavior at locations generally isolated from local anthropogenic contamination. Variations on time scales from hours to years are considered. Observations in tropical and polar regions suggest weak coupling between tropospheric and stratospheric ozone in these regions. At subtropical and mid-latitude stations, on the other hand, there appears to be stronger coupling between tropospheric and stratospheric ozone. A small diurnal variation in surface ozone at Samoa may indicate photochemical influence on the ozone budget there. Some of the year-to-year differences in surface ozone at the four stations indicate possible global influences on the tropospheric ozone budget. No significant long-term trends are apparent in the data, however.

Abstract

Ozone vertical profile measurements obtained from ozonesondes flown at Fiji, Samoa, Tahiti, and the Galapagos are used to characterize ozone in the troposphere over the tropical Pacific. There is a significant seasonal variation at each of these sites. At sites in both the eastern and western Pacific, ozone mixing ratios are greatest at almost all levels in the troposphere during the September-November season and smallest during March–May. The vertical profile has a relative maximum at all of the sites in the midtroposphere throughout the year (the largest amounts are usually found near the tropopause). This maximum is particularly pronounced during the September–November season. On average, throughout the troposphere, the Galapagos has larger ozone amounts than the western Pacific sites. A trajectory climatology is used to identify the major flow regimes that are associated with the characteristic ozone behavior at various altitudes and seasons. The enhanced ozone seen in the midtroposphere during September-November is associated with flow from the continents. In the western Pacific this flow is usually from southern Africa (although 10-day trajectories do not always reach the continent) but also may come from Australia and Indonesia. In the Galapagos the ozone peak in the midtroposphere is seen in flow from the South American continent and particularly from northern Brazil. High ozone concentrations within potential source regions and flow characteristics associated with the ozone mixing ratio peaks seen in both the western and eastern Pacific suggest that these enhanced ozone mixing ratios result from biomass burning. In the upper troposphere, low ozone amounts are seen with flow that originates in the convective western Pacific.

Abstract

From a network of sites, primarily in the Atlantic and Pacific Ocean regions, measurements of the surface ozone concentration yield information on the seasonal, synoptic, and diurnal patterns. These sites, generally removed from the effects of local pollution sources, show characteristics that typify broad geographical regions. At Barrow, AK; Mauna Loa, HI; American Samoa; and South Pole, data records of 15–20 years show trends that in all cases are a function of season. This dependence on season is important in understanding the causes of the long-term changes. At Barrow, the summer (July, August, September) increase of 1.7% per year is probably indicative of photochemical production. At South Pole, on the other hand, the summer (December, January, February) decrease is related to photochemical losses and enhanced transport from the coast of Antarctica. At all the sites there is a pronounced seasonal variation. In the Southern Hemisphere (SH), all locations which run from 14 to 90°S show a winter (July– August) maximum and summer minimum. In the Northern Hemisphere (NH) most of the sites show a spring maximum and autumn minimum. At Barrow (70°N) and Barbados (14°), however, the maxima occur during the winter, but for very different reasons. At many of the sites, the transport changes associated with synoptic scale weather patterns dominate the day-to-day variability. This is particularly pronounced at Bermuda and the more tropical sites. In the tropics, there is a very regular diurnal surface ozone cycle with minimum values in the afternoon maxima early in the morning. This appears to result from photochemical destruction during the day in regions with very low concentrations of nitrogen oxides. At Niwot Ridge, CO, and Mace Head, Ireland, there is clear evidence of photochemical ozone production in the summer during transport from known regional pollution sources.

Abstract

THE possible impact of pollution from North America and Europe on tropospheric ozone throughout the Northern Hemisphere is a major environmental concern1–4. We report here continuous measurements of ozone from Bermuda (32° N, 65° W) and Barbados (13° N, 60° W), which suggest that despite their proximity to the eastern US seaboard, natural processes rather than pollution control surface ozone in these regions. Although springtime daily average ozone concentrations at Bermuda are greater than 70 parts per billion (109) by volume (p.p.b.v.) and hourly values in 1989 sometimes exceeded the Canadian Air Quality limit of 80 p.p.b.v., trajectory analyses indicate that these high levels of ozone are transported from the unpolluted upper troposphere >5 km above the northern United States and Canada5. During the summer, when surface ozone concentrations over the eastern United States can exceed 70 p.p.b.v. owing to pollution6, typical values at Ber-muda are between 15 and 25 p.p.b.v. At Barbados, both the seasonal and diurnal variations in surface ozone are nearly identical to those at Samoa in the tropical South Pacific, where the isolation from anthropogenic sources7 and low levels of NOX (ref. 8) ensure that natural processes control surface ozone9–11.

Abstract

Measurements of the 13C/12C, D/H and 14C composition of atmospheric methane (CH4) between 1988 and 1995 are presented. The 13C/12C measurements represent the first global data set with time series records presented for Point Barrow, Alaska (71°N), Olympic Peninsula, Washington (48°N), Mauna Loa, Hawaii (20°N), American Samoa (14°S), Cape Grim, Australia (41°S), and Baring Head, New Zealand (41°S). North-south trends of the 13C/12C and D/H of atmospheric CH4 from air samples collected during oceanographic research cruises in the Pacific Ocean are also presented. The mean annual ?13C increased southward from about ?47.7 ‰ at 71°N to ?41.2 ‰ at 41°S. The amplitude of the seasonal cycle in ?13C ranged from about 0.4 ‰ at 71°N to 0.1 ‰ at 14°S. The seasonal ?13C cycle at sites in tropical latitudes could be explained by CH4 loss via reaction with OH radical, whereas at temperate and polar latitudes in the northern hemisphere seasonal changes in the ?13C of the CH4 source were needed to explain the seasonal cycle. The higher ?13C value in the southern (?47.2 ‰) versus northern (?47.4 ‰) hemisphere was a result of interhemispheric transport of CH4. A slight interannual ?13C increase of 0.02±0.005 ‰ yr?1 was measured at all sites between 1990 and 1995. The mean ?D of atmospheric CH4 was ?86±3 ‰ between 1989 and 1995 with a 10 ‰ depletion in the northern versus southern hemisphere. The 14C content of CH4 measured at 48°N increased from 122 to 128 percent modern between 1987 and 1995. The proportion of CH4 released from fossil sources was 18±9% in the early 1990s as derived from the 14C content of CH4.

Abstract

The exchange of CO2 between the atmosphere and tropical forest ecosystem of American Samoa was continuously monitored for 3 days in December 1988. The island was modeled as a simple wind-ventilated respiration chamber with CO2 input concentration, CO2 output concentration, and residence time as measured variables. Net ecosystem production rates were calculated by incorporating Gaussian vertical diffusion into the model. Nighttime respiration averaged 0.34 (±0.06) g C m?2 h?1; peak midday uptake was 0.85 (±0.23) g C m?2 h?1 . Thirty-nine percent (±30%) more carbon was assimilated by the ecosystem during the day than was released at night. The diurnal net ecosystem production averaged 1.5 g C m?2 d?1. The daytime CO2 exchange rate varied as the logarithm of incident solar radiation over a range of 30 W/m2 to 900 W/m2, with r2 = 0.87. Total ecosystem respiration equaled photosynthesis at a radiation intensity of 72 (±14) W/m2. The saturation intensity was 600 W/m2.

Abstract

We present a comprehensive estimate of nitrous oxide (N₂O) emissions using observations and models from 1995 to 2008. High-frequency records of tropospheric N₂O are available from measurements at Cape Grim, Tasmania; Cape Matatula, American Samoa; Ragged Point, Barbados; Mace Head, Ireland; and at Trinidad Head, California using the Advanced Global Atmospheric Gases Experiment (AGAGE) instrumentation and calibrations. The Global Monitoring Division of the National Oceanic and Atmospheric Administration/Earth System Research Laboratory (NOAA/ESRL) has also collected discrete air samples in flasks and in situ measurements from remote sites across the globe and analyzed them for a suite of species including N₂O. In addition to these major networks, we include in situ and aircraft measurements from the National Institute of Environmental Studies (NIES) and flask measurements from the Tohoku University and Commonwealth Scientific and Industrial Research Organization (CSIRO) networks. All measurements show increasing atmospheric mole fractions of N₂O, with a varying growth rate of 0.1–0.7% per year, resulting in a 7.4% increase in the background atmospheric mole fraction between 1979 and 2011. Using existing emission inventories as well as bottom-up process modeling results, we first create globally gridded a priori N₂O emissions over the 37 years since 1975. We then use the three-dimensional chemical transport model, Model for Ozone and Related Chemical Tracers version 4 (MOZART v4), and a Bayesian inverse method to estimate global as well as regional annual emissions for five source sectors from 13 regions in the world. This is the first time that all of these measurements from multiple networks have been combined to determine emissions. Our inversion indicates that global and regional N₂O emissions have an increasing trend between 1995 and 2008. Despite large uncertainties, a significant increase is seen from the Asian agricultural sector in recent years, most likely due to an increase in the use of nitrogenous fertilizers, as has been suggested by previous studies.

Abstract

The precision and accuracy of trends and seasonal cycles of CO2, as determined from grab samples, was investigated. First, the statistical aspects of infrequent (weekly) sampling were studied by simulating, via a partially random procedure, parallel time series of CO2 flask samples. These simulated flask series were compared to the continuous analyzer records from which they had been derived. The second approach to studying the uncertainties of flask records was to compare real flask results with simultaneous hourly mean concentrations of the in situ analyzers at the Geophysical Monitoring for Climatic Change observatories at Point Barrow, Mauna Loa, Samoa, and the south pole. The latter comparisons emphasized experimental, rather than statistical, errors. The uncertainties and sampling biases depend on the site and on the period of averaging. For monthly means the uncertainty varies from 0.2 to 0.6 ppm (one standard deviation, parts per million by volume), being largest for Barrow. Sampling biases for monthly means at Barrow and Mauna Loa are significant, up to 0.5 ppm. Experimental errors are the dominant error source for annual averages, and spurious interannual variations can be up to 0.4 ppm.

Abstract

A network of 10 southern hemisphere tropical and subtropical stations, designated the Southern Hemisphere Additional Ozonesondes (SHADOZ) project and established from operational sites, provided over 1000 ozone profiles during the period 1998–2000. Balloon-borne electrochemical concentration cell (ECC) ozonesondes, combined with standard radiosondes for pressure, temperature, and relative humidity measurements, collected profiles in the troposphere and lower to midstratosphere at: Ascension Island; Nairobi, Kenya; Irene, South Africa; Réunion Island; Watukosek, Java; Fiji; Tahiti; American Samoa; San Cristóbal, Galapagos; and Natal, Brazil. The archived data are available at: ? http://croc.gsfc.nasa.gov/shadoz?. In this paper, uncertainties and accuracies within the SHADOZ ozone data set are evaluated by analyzing: (1) imprecisions in profiles and in methods of extrapolating ozone above balloon burst; (2) comparisons of column-integrated total ozone from sondes with total ozone from the Earth-Probe/Total Ozone Mapping Spectrometer (TOMS) satellite and ground-based instruments; and (3) possible biases from station to station due to variations in ozonesonde characteristics. The key results are the following: (1) Ozonesonde precision is 5%. (2) Integrated total ozone column amounts from the sondes are usually to within 5% of independent measurements from ground-based instruments at five SHADOZ sites and overpass measurements from the TOMS satellite (version 7 data). (3) Systematic variations in TOMS-sonde offsets and in ground-based-sonde offsets from station to station reflect biases in sonde technique as well as in satellite retrieval. Discrepancies are present in both stratospheric and tropospheric ozone. (4) There is evidence for a zonal wave-one pattern in total and tropospheric ozone, but not in stratospheric ozone.

Abstract

The first view of stratospheric and tropospheric ozone variability in the Southern Hemisphere tropics is provided by a 3-year record of ozone soundings from the Southern Hemisphere Additional Ozonesondes (SHADOZ) network ( http://croc.gsfc.nasa.gov/shadoz). Observations covering 1998–2000 were made over Ascension Island, Nairobi (Kenya), Irene (South Africa), Réunion Island, Watukosek (Java), Fiji, Tahiti, American Samoa, San Cristóbal (Galapagos), and Natal (Brazil). Total, stratospheric, and tropospheric column ozone amounts usually peak between August and November. Other features are a persistent zonal wave-one pattern in total column ozone and signatures of the quasi-biennial oscillation (QBO) in stratospheric ozone. The wave-one is due to a greater concentration of free tropospheric ozone over the tropical Atlantic than the Pacific and appears to be associated with tropical general circulation and seasonal pollution from biomass burning. Tropospheric ozone over the Indian and Pacific Oceans displays influences of the waning 1997–1998 El Niño, seasonal convection, and pollution transport from Africa. The most distinctive feature of SHADOZ tropospheric ozone is variability in the data, e.g., a factor of 3 in column amount at 8 of 10 stations. Seasonal and monthly means may not be robust quantities because statistics are frequently not Gaussian even at sites that are always in tropical air. Models and satellite retrievals should be evaluated on their capability for reproducing tropospheric variability and fine structure. A 1999–2000 ozone record from Paramaribo, Surinam (6°N, 55°W) (also in SHADOZ) shows a marked contrast to southern tropical ozone because Surinam is often north of the Intertropical Convergence Zone (ITCZ). A more representative tropospheric ozone climatology for models and satellite retrievals requires additional Northern Hemisphere tropical data.

Abstract

The U.S. National Oceanic and Atmospheric Administration (NOAA) has operated a program to continuously monitor atmospheric CO2 at Cape Matatula, American Samoa, since January 1976. This paper describes the basic operational program and reports the data through 1987. Data sets are derived from hourly means which have been selected to represent baseline conditions. All hourly mean CO2 values (with flags indicating data selection status) are archived at NO AA's Geophysical Monitoring for Climatic Change (GMCC) laboratory in Boulder, Colorado; at the Carbon Dioxide Information and Analysis Center in Oak Ridge, Tennessee; and in the microfiche version of this paper. The record from the in situ analyzer is compared with that of flask samples obtained in various Ways. The overall 12-year record shows an average increase of 1.44 parts per million by volume per year. This increase amounts to 61% of the carbon dioxide emitted into the atmosphere by fossil fuel combustion during this period. The record is also characterized by the lack of a prominent seasonal cycle. The CO2 concentrations for the first half of each year are always more variable than the second 6 months, when the wind flow is dominated by strong southeasterly trades. The interannual variability of the CO2 growth rate correlates very well with that observed at other GMCC sites.

Abstract

SF₆ total columns were successfully retrieved from FTIR (Fourier transform infrared) measurements (Saint Denis and Maïdo) on Reunion Island (21°â€¯S, 55°â€¯E) between 2004 and 2016 using the SFIT4 algorithm: the retrieval strategy and the error budget were presented. The FTIR SF₆ retrieval has independent information in only one individual layer, covering the whole of the troposphere and the lower stratosphere. The trend in SF₆ was analysed based on the FTIR-retrieved dry-air column-averaged mole fractions (X_SF6) on Reunion Island, the in situ measurements at America Samoa (SMO) and the collocated satellite measurements (Michelson Interferometer for Passive Atmospheric Sounding, MIPAS, and Atmospheric Chemistry Experiment Fourier Transform Spectrometer, ACE-FTS) in the southern tropics. The SF₆ annual growth rate from FTIR retrievals is 0.265 ±â€¯0.013 pptv year⁻¹ for 2004–2016, which is slightly weaker than that from the SMO in situ measurements (0.285 ±â€¯0.002 pptv year⁻¹) for the same time period. The SF₆ trend in the troposphere from MIPAS and ACE-FTS observations is also close to the ones from the FTIR retrievals and the SMO in situ measurements.

Abstract

Profiles of CFC-11 (CCl₃F), CFC-12 (CCl₂F₂) and HCFC-22 (CHF₂Cl) have been obtained from Fourier transform infrared (FTIR) solar absorption measurements above the Saint-Denis (St Denis) and Maïdo sites at Réunion Island (21°â€¯S, 55°â€¯E) with low vertical resolution. FTIR profile retrievals are performed by the well-established SFIT4 program and the detail retrieval strategies along with the systematic/random uncertainties of CFC-11, CFC-12 and HCFC-22 are discussed in this study. The FTIR data of all three species are sensitive to the whole troposphere and the lowermost stratosphere, with the peak sensitivity between 5 and 10 km.

The ground-based FTIR data have been compared with the collocated Michelson Interferometer for Passive Atmospheric Sounding (MIPAS/ENVISAT) data and found to be in good agreement: the observed mean relative biases and standard deviations of the differences between the smoothed MIPAS and FTIR partial columns (6–30 km) are (−4.3 and 4.4 %), (−2.9 and 4.6 %) and (−0.7 and 4.8 %) for CFC-11, CFC-12 and HCFC-22, respectively, which are within the combined error budgets from both measurements. The season cycles of CFC-11, CFC-12 and HCFC-22 from FTIR measurements and MIPAS data show a similar variation: concentration is highest in February–April and lowest in August–October.

The trends derived from the combined St Denis and Maïdo FTIR time series are −0.86 ±â€¯0.12 and 2.84 ±â€¯0.06 % year⁻¹ for CFC-11 and HCFC-22, respectively, for the period 2004 to 2016, and −0.76 ±â€¯0.05 % year⁻¹ for CFC-12 for 2009 to 2016. These measurements are consistent with the trends observed by the National Oceanic and Atmospheric Administration (NOAA) Global Monitoring Division's (GMD) Halocarbons & other Atmospheric Trace Species Group (HATS) measurements at Samoa (14.2°â€¯S, 170.5°â€¯W) for CFC-11 (−0.87 ±â€¯0.04 % year⁻¹), but slightly weaker for HCFC-22 (3.46 ±â€¯0.05 %) year⁻¹ and stronger for CFC-12 (−0.60 ±â€¯0.02 % year⁻¹).