Global Tropospheric Experiment Research Articles

Ozone budget over the Amazon: Regional effects from biomass‐burning emissions

A one‐dimensional, time‐dependent, photochemical model is used in conjunction with data obtained during the dry‐season portion of NASA's Global Tropospheric Experiment and Brazil's Instituto Nacional de Pesquisas Espaciais (INPE) (National Institute for Space Research) Amazon Boundary Layer Experiment (ABLE 2A) to simulate the chemistry of the dry‐season Amazon troposphere. The background atmosphere, unperturbed by the presence of emissions from biomass burning, is simulated with inputs of surface sources and deposition of various species measured during ABLE 2A. The presence of haze layers over a region is simulated by the imposition of profiles of species characteristic of haze within the model for 12 hours. The inclusion of hydrocarbons within the modeled haze is found to approximately double the calculated in situ ozone production rate. The difference between the calculated total column ozone production rates in the haze simulation and the background simulation is the model‐predicted enhancement of the in situ ozone production due to regionally transported haze layers (up to 1000 km transport distance). The predicted enhancement of ozone is between 0.3 and 2.9 × 1011molecules O3 cm−2 s−1, near the range of observed rates of ozone increase over the Amazon Basin during the dry season. This suggests that the regional transport of haze during the southern tropical burning season is an important factor in explaining the increase of ozone observed annually during this period.

Rainwater and throughfall chemistry in a “terra firme” rain forest: Central Amazonia

During the Global Tropospheric Experiment (GTE)‐Amazon Boundary Layer Experiment (ABLE) 2B campaign in the Amazon basin, samples of rainwater and throughfall were obtained in a “terra firme” (nonflooded forest) rain forest at the Ducke Reserve (2°57'S, 59°58'W). The samples were collected during one wet period (April 1 to May 13, 1987) and one dry period (August 1 to October 1, 1987). All samples were analyzed for Na+, K+, Mg2+, Ca2+, NH4+, Cl− and SO42−, and pH. The rainwater was acidic, with a volume‐weighted mean pH of 4.6 for the two periods. Rainwater input from the dry period was 2 times greater for Na+, Mg2+, NH4+ and SO42− and about 4 times greater for K− than from the wet period. The ionic concentrations in throughfall were higher than those in rainwater, except for NH4+ during the dry period. This enrichment of throughfall is attributed to the interaction of precipitation with the forest canopy.

Aerosol characteristics and sources for the Amazon Basin during the wet season

As a part of the NASA Global Tropospheric Experiment (GTE), aerosols were sampled in the tropical rain forest of the Amazon Basin during the Amazon Boundary Layer Experiment (ABLE 2B) in April and May 1987, in the wet season, when no forest burning occurs. Fine (dp < 2.0 μm) and coarse (2.0 < dp < 15 μm) aerosol fractions were collected using stacked filter units, at three sites under the forest canopy and at three levels of a tower inside the jungle. Particle‐induced X ray emission (PIXE) was used to measure concentrations of 22 elements (Na, Mg, Al, Si, P, S, Cl, K, Ca, Ti, V, Cr, Mn, Fe, Ni, Cu, Zn, Br, Rb, Sr, Zr, and Pb). Morphological and trace element measurements of individual particles were carried out by automated electron probe X ray microanalysis. Gravimetric analysis was performed to obtain the fine and coarse aerosol mass concentration. Absolute factor analysis was used to interpret the large data set of the trace element concentrations and to obtain elemental source profiles. Hierarchical cluster analysis was used to derive groups of individual particles. The concentrations of soil dust related elements (Al, Si, Ti, Fe, Mn) were 5 times larger in the wet season compared to the 1985 ABLE 2A dry season experiment. Biogenic aerosol related elements in the fine fraction showed lower concentrations in the wet season. Fine aerosol mass concentration averaged only 2.1±0.7 μg m−3, while the average coarse mass concentration was 6.1±1.8 μg m −3. Sulphur concentrations averaged 76±14 ng m −3 in the fine fraction and 37±9 ng m −3 in the coarse fraction. Biogenic aerosol‐related elements were dominant under the forest canopy, while soil dust dominated at the top of the forest canopy. Only two factors explained about 90% of the data variability for the fine and coarse aerosol fractions. These were soil dust (represented mainly by Al, Si, Ti, Mn, and Fe) and biogenic aerosol (represented by K, P, Cl, S, Zn, and the aerosol mass concentration). Source profiles showed a homogeneous aerosol distribution with similar elemental compositions at the different sampling sites. Enrichment factor calculations revealed a soil dust elemental profile similar to the average bulk soil composition, and a biogenic component similar to the plant bulk elemental composition. Total aerosol mass source apportionment showed that biogenic particles account for 55–95% of the airborne concentrations. The analysis of individual aerosol particles showed that the biogenic particles consist of leaf fragments, pollen grains, fungi, algae, and other types of particles. Several groups of particles with K, Cl, P, S, and Ca as minor elements could easily be identified as biogenic particles on the basis of their morphology. Considering the vast area of tropical rain forests and the concentrations measured in this work, it is possible that biogenic particles can play an important role in the global aerosol budget and in the global biogeochemical cycles of various elements.

Ozone and aerosol distributions over the Amazon Basin during the wet season

Measurements of ozone (O3) and aerosols were made over the tropical rain forest of Brazil during the wet season in April–May 1987 as part of the NASA Global Tropospheric Experiment to study the Amazon boundary layer. Remote and in situ measurements of O3 and aerosols were made from aircraft on flights over Brazil in the vicinity of Manaus and between Manaus and Belem. Ozonesonde data were also obtained near Manaus. Ozone mixing ratios of <12 ppbv were found in the mixed layer during the wet season with no significant evidence of O3 produced from biomass burning or photochemistry. These values are lower than those found during the 1985 dry season by 6–8 ppbv. These low O3 mixing ratios indicate a strong removal process near the surface during the wet season. The region from the mixed layer top to 3 km in altitude had a slowly increasing O3 profile from 12 to 20 ppbv. On long‐range flights between Manaus and Belem, no significant difference was found in the distribution of O3 above the mixed layer between the inland tropical rain forest and the marine conditions near the coast. Within the mixed layer, there was a definite trend to lower O3 levels above the forest compared to over the ocean. This reflects the marked difference in the sinks for O3 over these two regions. The rate of growth of the mixed layer over the rain forest in the wet season was found to be ∼9 cm s−1, which is within the 7–10 cm s−1 range found for the dry season. There was no evidence of the trade wind inversion that was seen during the dry season, and due to frequent precipitation, the background aerosol loading was lower in the wet season than in the dry season.

An intercomparison of airborne nitric acid measurements

Results from an airborne intercomparison of techniques to measure tropospheric levels of nitric acid are discussed. The intercomparison was part of the National Aeronautics and Space Administration's Global Tropospheric Experiment and was conducted during the summer of 1986. Instruments intercompared included a denuder tube collection system (DENUDER) with chemiluminescent detection, a niylon filter collection system (FILTER) with ion chromatography detection, and a tunable diode laser (TDLAS) multipath absorption system. Intercomparison of investigators' calibration standards were also performed as part of the test protocol. While results were somewhat “soft” and data sparse, these tests suggested that the TDLAS measurements might be high compared to the other techniques. Airborne intercomparisons were conducted predominately in the free troposphere and included encounters with marine and continental air masses. While the intercomparisons included mixing ratios to 1000 parts per trillion by volume (pptv), the majority of the results were for mixing ratios of <300 pptv. The TDLAS participated in an intercomparison of NO2 instruments (major focus) that was also conducted during the same flights. As a result the TDLAS data set is limited. Further, a significant fraction of the nitric acid measurements were below the TDLAS detection limit (75 pptv as configured for these tests). While the lack of simultaneous measurements from the three instruments limits the conclusions that can be drawn, it is clear that there can be substantial disagreement among the three techniques, even at mixing ratios above their respective detection limits. Equally clear is that at mixing ratios below 150 pptv there is very little correlation between their results. Based on these observations, an overall conclusion from the intercomparison is that none of the HNO3 techniques can be identified to unambiguously (e.g., 20% accuracy) provide measurements of HNO3 at levels often encountered in the free troposphere (e.g., 100 pptv). However, at the more elevated levels of HNO3 (e.g., >150 pptv), both the FILTER and DENUDER techniques reported the same levels of nitric acid, while as suggested by the results from the standards intercomparison, the TDLAS reported higher nitric acid values than the other two techniques.

An intercomparison of airborne PAN measurements

As part of the NASA Tropospheric Chemistry Program a series of field intercomparisons have been initiated to evaluate state‐of‐the‐art capability for measuring key tropospheric species. These intercomparisons, designated as Chemical Instrumentation Test and Evaluation (CITE), are conducted as part of NASA's Global Tropospheric Experiment. The objectives of the second series of instrument tests, CITE 2, were to evaluate instrumentation for measuring NO2, HNO3, and peroxyacetyl nitrate (PAN) and to determine for various tropospheric environments the relative abundances and partitioning among the major nitrogen species. This paper summarizes the results from the PAN instrument intercomparisons. Other results are addressed in companion papers. Both PAN instruments use the same detection principle of electron capture gas chromatography of a cryogenically enriched sample of ambient air. NASA Ames Research Center and the National Center for Atmospheric Research were responsible for the respective instruments. The intercomparisons included three exchanges of standards and 13 intercomparison flights in which a variety of types of air masses were sampled. Nine flights were based from Ames Research Center, California, and the remaining four were ferry flights between Ames and Wallops Flight Center, Virginia (aircraft home base). Flight altitudes ranged from 150 to 5000 m above ground level. All flights but one were during daylight hours. PAN mixing ratios during the flight intercomparison periods were generally <300 parts per trillion by volume (pptv), and about 40% of the results for mixing ratios were <100 pptv. At mixing ratios of <100 pptv the two instruments agreed on the average to about 17 pptv with a 95% confidence interval of ±9 pptv. Instrument agreement at PAN levels of 100–300 pptv was of the order of 25% with a confidence interval of ±6%. These levels of agreement are within expected limits based on the stated accuracy and precision of the two instruments. However, it is noted that for some of the individual intercomparison data periods, agreement was outside expected levels.

An intercomparison of airborne nitrogen dioxide instruments

Results from an airborne intercomparison of techniques to measure tropospheric levels of nitrogen dioxide (NO2) are discussed. The intercomparison was part of the National Aeronautics and Space Administration's Global Tropospheric Experiment and was conducted during the summer of 1986. Instruments intercompared included a two‐photon nitric oxide (NO) laser‐induced fluorescence system with laser photolysis of NO2 to NO, an NO/O3 chemiluminescence detector using FeSO4 for conversion of NO2 to NO, an NO/O3 chemiluminescence detector with arc lamp photolysis of NO2 to NO, and a tunable diode laser multipath absorption system. All intercomparisons were for NO2 mixing ratios of <200 pptv with most at mixing ratios of <100 pptv. The FeSO4 converter was found to convert peroxyacetyl nitrate (PAN) to NO, resulting in NO2 values a factor of 2–3 higher than reported by the other techniques. Thus the FeSO4 converter data are excluded from the analyses. Intercomparison data were analyzed in various mixing ratio ranges. Good correlation was observed between the remaining three instruments for those data sets which included mixing ratios to 100 or 200 pptv, showing on the average a 30–40% level of agreement among the techniques. However, when the data were restricted to mixing ratios of <50 pptv, little correlation among the measurements was observed. Even though correlations were poor at mixing ratios of <50 pptv, the tunable diode laser system tended to be high compared to data reported by the two‐photon laser and arc lamp chemiluminescence systems, and agreement between the latter two instruments was generally better than 20 pptv with an equal tendency for one to be high relative to the other.

An intercomparison of airborne nitric oxide measurements: A second opportunity

Results from an airborne intercomparison of techniques to measure tropospheric levels of NO are discussed. The intercomparison was part of the National Aeronautics and Space Administration's Global Tropospheric Experiment and was conducted during the summer of 1986. Instruments intercompared included a two‐photon laser‐induced fluorescence system and two NO/O3 chemiluminescence detectors. These three instruments also participated in the NO intercomparisons conducted during the Chemical Instrumentation Test and Evaluation (CITE) 1 mission in 1983–1984, and therefore the current results are a revisit to the question of how well NO can be measured from an aircraft in remote tropospheric environments. The intercomparisons were weighed to mixing ratios less than 20 pptv. Results from CITE 2 were similar to those of CITE 1. The most noteworthy observation common to both campaigns is that at these low mixing ratios, agreement among the three instruments is almost always within about 15 or 20 pptv for sampling periods of 1–6 min. Analyses of multipoint data sets suggest that on the average the difference between data from any pair of the instruments at the low mixing ratios is about 5–7 pptv. Since this agreement was obtained among instruments using fundamentally different detection principles (chemiluminescent and laser) and the data suggested that all provided equally valid measurements of NO, the observed level of agreement perhaps represents the uncertainity in the current measurement of low mixing ratio ambient NO. The major question which must be addressed by the scientific community is the influence of, for example, a 5‐pptv uncertainty in NO at 10 pptv in photochemistry studies, nitrogen budget studies, and so on, in the “clean” remote troposphere.

Trace element concentrations and size distribution of biogenic aerosols from the amazon basin during the wet season

Atmospheric aerosols were sampled in the tropical rain forest of the Amazon Basin during April and May, 1987 (wet season) as part of the NASA Global Tropospheric Experiment (GTE), during the Amazon Boundary Layer Experiment (ABLE-2B). A special fine particle aerosol sampler and 6-stage single orifice cascade impactors were used for the aerosol collections. The samples were analyzed for 24 elements (Na, Mg, Al, Si, P, S, Cl, K, Ca, Ti, V, Cr, Mn, Fe, Ni, Cu, Zn, Ga, Se, Br, Rb, Sr, Zr, and Pb) by particle-induced X-ray emission (PIXE). Absolute principal factor analysis was used to interpret the fine particle aerosol elemental concentrations, and to obtain elemental source profiles. The concentrations of the fine mode soil dust related elements (Al, Ti, Mn, and Fe) were more than 10 times larger in the wet season than in the dry season. The biogenic aerosol related elements (e.g. P, S, K, and Zn) in the fine mode showed strongly reduced concentrations in the wet season. Sulphur concentrations averaged 92 ± 54 ng m 3 in the fine mode aerosol. The concentrations of soil dust related elements were 80% higher during daytime than during night, whereas the biogenic related elements showed much lower levels during day than during night. Two factors explained more than 92% of the data variability for the day and night fine particle samples. These factors were soil dust (represented mainly by Al. Si, Ti, Mn. and Fe) and biogenic related aerosol (with K, P, S, and Zn). Source profiles were obtained for the fine mode aerosol, and the soil dust factor had a similar elemental composition as average crustal rock. The size distributions of the soil dust related elements, as measured at three different levels (ground level, 28 and 45 m), were very similar, whereas for the biogenic related elements some differences as a function of height were observed. The sulphur size distribution was clearly bimodal, but the fine mode was significantly reduced at ground level. Considering the concentrations measured in this work and the large area of the tropical rain forests, biogenic aerosol particles can play an important role in the global aerosol budget and in the global biogeochemical cycles of various elements.

Ozone precursors and ozone photochemistry over eastern North Pacific during the spring of 1984 based on the NASA GTE/CITE 1 airborne observations

Simultaneous, high‐resolution measurements of O3, NO, CO, dew point temperature, and UV flux obtained during the NASA Global Tropospheric Experiment Chemical Instrumentation Test and Evaluation (GTE/CITE 1) spring 1984 airborne field exercise over the eastern North Pacific Ocean are analyzed. Mid‐tropospheric CO, O3, and NO mixing ratios averaged about 120 parts per billion by volume (ppbv), 50 ppbv, and 10 parts per trillion by volume (pptv), respectively. Statistical analysis of the high‐resolution data indicates the existence of two ozone sources: one related to the downward transport of ozone‐rich air from the upper troposphere and stratosphere and the other to the transport of ozone‐rich air from the continents. Modeling calculations based on these average levels imply that from the surface to about 8 km, photochemical reactions probably supplied a net sink of ozone to the region overlying the eastern North Pacific Ocean during the sampling period. However, because the NO levels measured during the flights were frequently at or near the detection limit of the instruments and because our results are very sensitive to the absolute NO levels and their temporal variability, our conclusion must be considered provisional.

NO and NO2 in the troposphere: Technique and measurements in regions of a folded tropopause

During the 1984 spring program of the NASA Global Tropospheric Experiment, measurements of NO, NO2, O3, and CO were made during two aircraft flights that encountered tropopause fold events. The technique used to measure NOx (NO + NO2) is described. In the neighborhood of both tropopause fold events, CO and O3 were strongly anticorrelated [Danielsen et al., 1987; Hipskind et al., 1987]. In one fold, encountered over the eastern Pacific Ocean at night, NOx was positively correlated with O3, negatively correlated with the dew point, and negatively correlated with CO, consistent with the stratospheric origin of the air mass. In this fold at altitudes between 5.5 and 6.0 km, NOx reached mixing ratios near 150 parts per trillion by volume (pptv), considerably larger than the levels of 10–50 pptv in the air external to the fold. In contrast, in a daytime encounter with a fold over the southwestern United States at altitudes of 6.7–8.8 km, NOx did not correlate well with CO, O3, or dew point, but remained roughly constant at levels of 100–200 pptv. Outside of the fold, in a region of strong convective activity, NOx peaked to just over 500 pptv. It appears that mixing of tropospheric air containing elevated NOx weakened the expected trends for the fold over the continent compared to the fold over the ocean, and therefore NOx may not always be a good tracer of air of recent stratospheric origin. However, the observations emphasize that the stratospheric source of NOx acts to introduce NOx over a short period and through a large vertical region of the troposphere, not just near the tropopause, as is assumed in many tropospheric models.

Tropospheric nitric oxide measurements over the Amazon Basin

Horizontal and vertical distributions of nitric oxide (NO) were measured over the Amazon Basin during NASA's Global Tropospheric Experiment (GTE) Amazon Boundary Layer Experiment (ABLE 2A) mission in July–August 1985. During transit flights between the Virginia coast and Manaus, Brazil, NO mixing ratios were 12–15 parts per trillion by volume (pptv) at 5 km altitude. Values up to 200 pptv were observed in electrically active clouds. During longitudinal surveys over the Amazon region, NO mixing ratios in the lower planetary boundary layer decreased from 25–60 pptv over the central basin to 10–12 pptv in coastal regions. In the convective cloud layer or free troposphere, NO mixing ratios averaged 13 pptv in regions not influenced by biomass burning. No longitudinal trend above the mixed layer could be detected. A steep negative gradient with increasing altitude was noted within the mixed layer before midday. Mixing ratios decreased from 60 pptv at 0.2 km to about 15 pptv at the top of the mixed layer (1 km). No further change in mixing ratio with altitude through the convective cloud layer and lower edge of the free troposphere could be detected at this time. By midday, growth of the mixed layer height and enhanced mixing reduced the gradient, and evidence for mixing of NO into the convective cloud layer was noted.

Boundary layer ozone: An airborne survey above the Amazon Basin

This paper discusses ozone data obtained in the Amazon Basin during July and August 1985 as part of NASA's Global Tropospheric Experiment (GTE) Amazon Boundary Layer Experiment (ABLE 2A). ABLE 2A, based at Manaus, Brazil, was a concentrated site study over the Amazon Basin to investigate source/sink relationships between the tropical forest and the troposphere during non‐biomass‐burning conditions. Ozone data obtained in the mixed layer above the forest canopy (100–2000 m altitude) in the Manaus area are discussed. In addition, profiles obtained during Amazon Basin flights from Belem (50°W) to Tabatinga (70°W), Brazil, are analyzed to determine any cross‐basin effects. The ozone discussions are primarily centered on the mixed layer. Companion papers discuss ozone behavior in the forest canopy and cross‐basin observations above the mixed layer. The data clearly show the tropical forest to be a strong ozone sink. Within the mixed layer, ozone gradients are observed with ozone values, during daylight, in the range of 10–20 ppbv. Amazon cross‐basin (70°–50°W) ozone observations are similar to those over the forest at Manaus (60°W). Near the Atlantic coast a forest‐to‐marine transition zone is noted within the mixed layer. Using a box model calculation for the mixed layer and for midmorning times, ozone loss rates are calculated to be as large as 5×1012 molecules s−1 cm−2, with a midmorning average of 1.6×1012 molecules s−1 cm−2.

Composition and sources of aerosols from the Amazon Basin

Aerosols were sampled in the Amazon Basin, as part of the Global Tropospheric Experiment (GTE), during the Amazon Boundary Layer Experiment (ABLE 2A) in July–August 1985. Fine‐ and coarse‐particle fractions were analyzed for 22 elements by particle‐induced X ray emission. Gravimetric mass, black carbon, sulfate, and nitrate concentrations were also determined. Morphological and trace element measurements of individual particles were carried out by automated electron probe X ray microanalysis. Various receptor models, including multivariate methods and a chemical mass balance model, were employed in the interpretation of the bulk trace element concentrations. Three factors explained over 85% of the variability of fine‐ and coarse‐mode variables. On the basis of the elemental composition of the factors, two could be identified as plant related, and the third was a soil dust component. Of the coarse‐mode aerosol mass concentration (of 7.6±1.6 μg/m3), 62% could be attributed to aerosols released by the vegetation and 11% to soil dust. In the fine mode, soil dust accounted for less than 10% of the measured mass concentration (of 6.8±3.9 μg/m3). The variables related to the plant component were K, P, S, Ca, Mg, Cl, Rb, and the gravimetric mass. The elemental profile of the plant component resembled the bulk plant composition. By single‐particle analysis coupled with hierarchical cluster analysis, six to nine different biogenic‐related particle groups could be identified in the fine‐ and coarse‐aerosol modes. Almost all particle types consisted predominantly of carbonaceous material, with trace amounts of K, S, Ca, P, Cl, and Na. Only one group, comprising less than 11% of the total number of particles, consisted of soil dust–related aerosol.

Tropospheric ozone and aerosol distributions across the Amazon Basin

Ozone and aerosol distributions were measured during July–August 1985 over the tropical rain forest of Brazil as part of the NASA Global Tropospheric Experiment to study the Amazon boundary layer. Remote and in situ measurements of O3 and aerosols were made from a NASA Electra aircraft on several long‐range flights spanning different areas between Tabatinga and Belem, Brazil. Continuous O3 distributions were obtained between the aircraft altitude and the ground with an airborne differential absorption lidar (DIAL) system. Aerosol distributions were also continuously measured above and below the aircraft with the DIAL system. In situ O3 measurements were made on the aircraft and from ground‐launched ozonesondes at Manaus and Natal. Large‐scale variations in the vertical and horizontal distributions of O3 and aerosols were observed on nearly all flights over the Amazon Basin, with O3 exceeding 50 parts per billion by volume (ppbv) in some regions. Both positive and negative correlations were observed between O3 mixing ratios and aerosol concentrations. In nearly all cases, when O3 and aerosols were negatively correlated, this represented clean midtropospheric air, and when they were positively correlated, the air mass had undergone photochemical O3 production as a result of biomass burning. A 59% increase in the planetary boundary layer (PBL) O3 level was observed between the initial Manaus‐Belem flights on July 23–24, 1985 and the later flights on August 8–9, 1985. This was attributed to the increase in biomass burning near the Rio Amazonas and its tributaries and in savannah regions south of the Amazon Basin. Flights to the west of Manaus measured enhanced O3 and aerosol levels near the Rio Solimões, while the area sampled upwind of the river exhibited lower O3 levels. This was explained by the increased incidence of biomass burning near the river. This paper also examines the variability of the trade wind inversion (TWI) height across the Amazon Basin and the influence of O3 levels above the TWI on the budget of O3 in the PBL. Measurements reported for the early dry season characterize the background distribution of O3 and aerosols in the PBL prior to the onset of extensive biomass burning. These data provide the basis for a basin‐scale estimate of photochemical O3 production from biomass‐burning emissions.

Fast‐response, high‐precision carbon monoxide sensor using a tunable diode laser absorption technique

A tunable diode laser instrument denoted as DACOM (Differential Absorption CO Measurement) has been developed to meet the fast‐response, high‐precision CO measurement needs of the GTE (Global Tropospheric Experiment) program. Under the GTE program, DACOM participated in the three field missions of CITE 1 (Chemical Instrumentation Test and Evaluation 1), a project involving the intercomparison of trace gas measurement techniques. DACOM performance, including analyses of measurement error sources, is discussed for the ground‐based mission at Wallops Island, Virginia (summer 1983), and two missions on the NASA CV‐990 (fall 1983 and spring 1984). Examples of fast‐response (≈1 s), high‐precision (±1 part per billion by volume, ±1.5% of reading) airborne data are included to illustrate the capability of this instrument.

Airborne intercomparison of carbon monoxide measurement techniques

Results from an airborne intercomparison of techniques to measure tropospheric levels of carbon monoxide (CO) are discussed. The intercomparison was conducted as part of the National Aeronautics and Space Administration's Global Tropospheric Experiment and included a laser differential absorption method and two grab sample/gas chromatograph methods. Measurements were obtained during approximately 90 flight hours, during which the CO mixing ratios ranged from about 60 to 140 ppbv. The level of agreement observed for the ensemble of measurements was well within the overall accuracy stated for each instrument. The correlation observed between the measurements from the respective pairs of instruments ranged from 0.85 to 0.98, with no evidence for the presence of either a constant or proportional bias between any of the instruments.

Measurements of nitric oxide in the boundary layer and free troposphere over the Pacific Ocean

Measurements of NO and O3 are presented from 13 aircraft flights made over the Pacific Ocean in the autumn of 1983 during one phase of the NASA Global Tropospheric Experiment (GTE). All of the flights were made between 15° and 42°N and from the coast of California to west of the Hawaiian Islands. Within the upper marine boundary layer the median daytime mixing ratio of NO was near 1 part per trillion by volume (pptv). As well, values of NO less than 10 pptv were often observed up to altitudes near 6 km. Thus for the location and season of the measurements, a net photochemical destruction of O3 would be anticipated for the boundary layer region and to altitudes of 2–3 km. At higher altitudes of 7–11 km in the free troposphere, larger mixing ratios and greater variability were usually observed for NO. Both features are consistent with observed examples of injection of NO and O3 from the lower stratosphere and with the injection of NO from towering, electrically active, cumulonimbus clouds.

Carbon monoxide measurements over the eastern Pacific during GTE/CITE 1

As part of the Global Tropospheric Experiment's Chemical Instrumentation Test and Evaluation (GTE/CITE 1) intercomparison, carbon monoxide (CO) measurements were made from the NASA CV‐990 aircraft during the fall of 1983 and again in the spring of 1984. The experimental measurements for CO obtained during those flight series over the eastern and mid‐Pacific are presented here. Data were acquired from 10° to 20°N latitude over the mid‐Pacific and from 30° to 37°N latitude over the eastern Pacific off the coast of California. A seasonal variation of approximately 34 parts per billion by volume was measured over the altitudes and latitudes sampled, and a small latitudinal variation was also noted. The data are discussed in terms of the meteorological context in which they were collected.

Air chemistry over the tropical forest of Guyana

The tropical forests of the world are hypothesized to be an important source and/or sink for a number of atmospheric gas and aerosol species. As part of the National Aeronautics and Space Administration's Global Tropospheric Experiment, an aircraft flight (June 27, 1984) was conducted over the wet tropical forest of Guyana for purposes of characterizing the forest boundary layer. Instrumentation onboard the NASA Electra aircraft included measurement systems for a variety of chemical species, including ozone, carbon monoxide, dimethylsulfide, nonmethane hydrocarbons, and aerosols. The data reported represent the first comprehensive characterization of the wet tropical forest boundary layer from an aircraft platform. The data indicate that the boundary layer is a source of carbon monoxide, isoprene, and dimethylsulfide as well as being a sink for ozone. Reported aerosol data, including number density, mass concentration, and composition, indicate an increased aerosol presence in the boundary layer relative to the overriding troposphere. From an analysis of the aerosol composition this increase is the result of direct emissions from the forest as well as from various photochemical processes. The data are discussed in terms of their significance in the understanding of the wet tropical forest boundary layer as a source or sink for various species important to tropospheric chemistry.