Climate Monitoring And Diagnostics Laboratory Research Articles

Carbon dioxide content in the atmospheric thickness over central Eurasia (Issyk Kul Monitoring Station)

The refined data obtained from the spectroscopic measurements of carbon dioxide in the column of the continental atmosphere over the Issyk Kul Monitoring Station during the period 1980–2006 and the results of their comparison with the data obtained from the measurements of carbon dioxide in air samples and with the mean zonal empirical model of the Climate Monitoring and Diagnostics Laboratory (CMDL) are given. Seasonal variations and a long-term trend of carbon dioxide concentration in the atmospheric thickness over a 25-year period of measurements are analyzed. The monthly mean concentration of CO2 is increased by ∼40.5 ppm, and the linear-trend index is 1.62 ppm per year. The results of the aircraft measurements of CO2 concentration in air samples are, on the average, in agreement with the data obtained from the spectroscopic measurements of carbon dioxide concentration in the atmospheric column. The CO2 concentration in the surface air varies from day to day, and only its minimum values coincide with the CO2 concentration in the atmospheric thickness. The results of measurements of CO2 concentration in the atmospheric thickness and in the atmospheric surface layer over the KZD and KZM stations nearest to each other are, on the whole, in disagreement; moreover, the KZD and KZM data are inconsistent. The CO2 concentration in the atmospheric thickness is, on the average, 1–2% higher than that obtained with the CMDL model for 42.6° N latitude. The coefficient of correlation between the measurement results and model data is high (r= 0.95).

Estimating uncertainty of the WMO mole fraction scale for carbon dioxide in air

The current WMO CO2Mole Fraction Scale consists of a set of 15 CO2‐in‐air primary standard calibration gases ranging in CO2mole fraction from 250 to 520 μmol mol−1. Since the WMO CO2Expert Group transferred responsibility for maintaining the WMO Scale from the Scripps Institution of Oceanography (SIO) to the Climate Monitoring and Diagnostics Laboratory (CMDL) in 1995, the 15 WMO primary standards have been calibrated, first at SIO and then at regular intervals, between 1 and 2 years, by the CMDL manometric system. The uncertainty of the 15 primary standards was estimated to be 0.069 μmol mol−1(one‐sigma) in the absolute sense. Manometric calibrations results indicate that there is no evidence of overall drift of the Primaries from 1996 to 2004. In order to lengthen the useful life of the Primary standards, CMDL has always transferred the scale via NDIR analyzers to the secondary standards. The uncertainties arising from the analyzer random error and the propagation error due to the uncertainty of the reference gas mole fraction are discussed. Precision of NDIR transfer calibrations was about 0.014 μmol mol−1from 1979 to present. Propagation of the uncertainty was calculated theoretically. In the case of interpolation the propagation error was estimated to be between 0.06 and 0.07 μmol mol−1when the Primaries were used as the reference gases via NDIR transfer calibrations. The CMDL secondary standard calibrations are transferred via NDIR analyzers to the working standards, which are used routinely for measuring atmospheric CO2mole fraction in the WMO Global Atmosphere Watch monitoring program. The uncertainty of the working standards was estimated to be 0.071 μmol mol−1in the one‐sigma absolute scale. Consistency among the working standards is determined by the random errors of downward transfer calibrations at each level and is about 0.02 μmol mol−1. For comparison with an independent absolute scale, the five gravimetric standards from the National Institute for the Environmental Studies (NIES) in Tsukuba, Japan, ranging in CO2mole fraction from 350 to 390 μmol mol−1have been calibrated relative to the CMDL secondary standards. The average and standard deviation of the differences between the NIES gravimetric and CMDL analyzed CO2mole fraction are 0.004 ± 0.03 μmol mol−1.

Conversion of NOAA atmospheric dry air CH4 mole fractions to a gravimetrically prepared standard scale

Sixteen mixtures of methane (CH4) in dry air were prepared using a gravimetric technique to define a CH4 standard gas scale covering the nominal range 300–2600 nmol mol−1. It is designed to be suitable for measurements of methane in air ranging from those extracted from glacial ice to contemporary background atmospheric conditions. All standards were prepared in passivated, 5.9 L high‐pressure aluminum cylinders. Methane dry air mole fractions were determined by gas chromatography with flame ionization detection, where the repeatability of the measurement is typically better than 0.1% (≤1.5 nmol mol−1) for ambient CH4 levels. Once a correction was made for 5 nmol mol−1 CH4 in the diluent air, the scale was used to verify the linearity of our analytical system over the nominal range 300–2600 nmol mol−1. The gravimetrically prepared standards were analyzed against CH4 in air standards that define the Climate Monitoring and Diagnostics Laboratory (CMDL) CMDL83 CH4 in air scale, showing that CH4 mole fractions in the new scale are a factor of (1.0124 ± 0.0007) greater than those expressed in the CMDL83 scale. All CMDL measurements of atmospheric CH4 have been adjusted to this new scale, which has also been accepted as the World Meteorological Organization (WMO) CH4 standard scale; all laboratories participating in the WMO Global Atmosphere Watch program should report atmospheric CH4 measurements to the world data center on this scale.

Long-term trend of [formula omitted] at northern mid-latitudes: Comparison between ground-based infrared solar and surface sampling measurements

We report average tropospheric CH 4 volume mixing ratios retrieved from a 27 year time series of high spectral resolution infrared solar absorption measurements recorded between May 1977 and July 2004 at the US National Solar Observatory station on Kitt Peak ( 31 . 9 ∘ N , 111 . 6 ∘ W , 2.09 km altitude) and their comparison with surface in situ sampling measurements recorded between 1983 and 2004 at the Climate Monitoring and Diagnostics Laboratory (CMDL) station at Niwot Ridge, Colorado ( 40 . 0 ∘ N , 105 . 5 ∘ W , 3013 m altitude). The two measurement sets therefore overlap for the 1983–2004 time period. An average tropospheric volume mixing ratios of 1814 ± 48 ppbv ( 1 ppbv = 10 - 9 per unit volume) has been derived from the solar absorption time series with a best-fit increase rate trend equal to 8.26 ± 2.20 ppbv yr - 1 in 1983 decreasing to 1.94 ± 3.69 ppbv yr - 1 in 2003. The CMDL measurements also show a continuous long-term CH 4 volume mixing ratio rise, with subsequent slowing down. A mean ratio of the retrieved average tropospheric volume mixing ratio to the CMDL volume mixing ratio for the overlapping time period of 1.038 ± 0.034 indicates agreement between both data sets within the quantified experimental errors.

Boreal forest fires in 1997 and 1998: a seasonal comparison using transport model simulations and measurement data

Abstract. Forest fire emissions have a strong impact on the concentrations of trace gases and aerosols in the atmosphere. In order to quantify the influence of boreal forest fire emissions on the atmospheric composition, the fire seasons of 1997 and 1998 are compared in this paper. Fire activity in 1998 was very strong, especially over Canada and Eastern Siberia, whereas it was much weaker in 1997. According to burned area estimates the burning in 1998 was more than six times as intense as in 1997. Based on hot spot locations derived from ATSR (Along Track Scanning Radiometer) data and official burned area data, fire emissions were estimated and their transport was simulated with a Lagrangian tracer transport model. Siberian and Canadian forest fire tracers were distinguished to investigate the transport of both separately. The fire emissions were transported even over intercontinental distances. Due to the El Niño induced meteorological situation, transport from Siberia to Canada was enhanced in 1998. Siberian fire emissions were transported towards Canada and contributed concentrations more than twice as high as those due to Canada's own CO emissions by fires. In 1998 both tracers arrive at higher latitudes over Europe, which is due to a higher North Atlantic Oscillation (NAO) index in 1998. The simulated emission plumes are compared to CMDL (Climate Monitoring and Diagnostics Laboratory) CO2 and CO data, Total Ozone Mapping Spectrometer (TOMS) aerosol index (AI) data and Global Ozone Monitoring Experiment (GOME) tropospheric NO2 and HCHO columns. All the data show clearly enhanced signals during the burning season of 1998 compared to 1997. The results of the model simulation are in good agreement with ground-based as well as satellite-based measurements.

Long-term evolution in the tropospheric concentration of chlorofluorocarbon 12 (CCl 2F 2) derived from high-spectral resolution infrared solar absorption spectra: retrieval and comparison with in situ surface measurements

The average tropospheric volume mixing ratios of chlorofluorocarbon 12 (CCl 2F 2) have been retrieved from high-spectral resolution ground-based infrared solar-absorption spectra recorded from March 1982 to October 2003 with the McMath Fourier transform spectrometer at the US National Solar Observatory facility on Kitt Peak in southern Arizona (31.9°N, 111.6°W, 2.09 km altitude). The retrievals are based on fits to the unresolved ν 8 band Q-branches near 922 cm - 1 using the SFIT2 retrieval algorithm. The annual increase rate was equal to ( 16.88 ± 1.37 ) parts per trillion ( 10 - 12 ) by volume at the beginning of the time series, March 1982, or ( 4.77 ± 0.04 ) % , 1 sigma, declining progressively to ( 2.49 ± 1.24 ) parts per trillion, by volume at the end, October 2003, or ( 0.46 ± 0.24 ) % , 1 sigma. Average tropospheric mixing ratios from the solar spectra have been compared with average surface flask and in situ sampling measurements from the Climate Monitoring and Diagnostics Laboratory (CMDL) station at Niwot Ridge, CO, (USA) (40.0°N, 105.5°W, 3013 m altitude). The average ratio and standard deviation of the monthly means of the retrieved tropospheric mixing ratios relative to the CMDL surface mixing ratios is ( 1.01 ± 0.03 ) for the overlapping time period. Both datasets demonstrate the progressive impact of the Montreal protocol and its strengthening amendments on the trend of CCl 2F 2, though a tropospheric decrease has yet to be observed.

Constraints on Asian and European sources of methane from CH4‐C2H6‐CO correlations in Asian outflow

Aircraft observations of Asian outflow from the Transport and Chemical Evolution Over the Pacific (TRACE‐P) aircraft mission over the NW Pacific (March and April 2001) show large CH4 enhancements relative to background, as well as strong CH4‐C2H6‐CO correlations that provide signatures of regional sources. We apply a global chemical transport model simulation of the CH4‐C2H6‐CO system for the TRACE‐P period to interpret these observations in terms of CH4 sources and to explore in particular the unique constraints from the CH4‐C2H6‐CO correlations. We use as a priori a global CH4 source inventory constrained with National Oceanic and Atmospheric Administration (NOAA) Climate Monitoring and Diagnostics Laboratory (CMDL) surface observations [Wang et al., 2004]. We find that the observed CH4 concentration enhancements and CH4‐C2H6‐CO correlations in Asian outflow in TRACE‐P are determined mainly by anthropogenic emissions from China and Eurasia (defined here as Europe and eastern Russia), with only little contribution from tropical sources (wetlands and biomass burning). The a priori inventory overestimates the observed CH4 enhancements and shows regionally variable biases for the CH4/C2H6 slope. The CH4/CO slopes are simulated without significant bias. Matching both the observed CH4 enhancements and the CH4‐C2H6‐CO slopes in Asian outflow requires increasing the east Asian anthropogenic source of CH4, and decreasing the Eurasian anthropogenic source, by at least 30% for both. The need to increase the east Asian source is driven by the underestimate of the CH4/C2H6 slope in boundary layer Chinese outflow. The Streets et al. [2003] anthropogenic emission inventory for east Asia fits this constraint by increasing CH4 emissions from that region by 40% relative to the a priori, largely because of higher livestock and landfill source estimates. Eurasian sources (mostly European) then need to be reduced by 30–50% from the a priori value of 68 Tg yr−1. The decrease of European sources could result in part from recent mitigation of emissions from coal mining and landfills.

Validation of Parameterized Algorithms Used to Derive TRMM–CERES Surface Radiative Fluxes

Abstract Parameterized shortwave and longwave algorithms developed at the Langley Research Center have been used to derive surface radiative fluxes in the processing of the Clouds and the Earth's Radiant Energy System (CERES) data obtained from flight aboard the Tropical Rainfall Measuring Mission (TRMM) satellite. Retrieved fluxes were validated on an instantaneous–footprint basis using coincident surface measurements obtained from the Atmospheric Radiation Measurement (ARM) program's Southern Great Plains (SGP) central facility, the ARM/SGP network of extended facilities, and a number of surface sites of the Baseline Surface Radiation Network (BSRN) and the Climate Monitoring and Diagnostics Laboratory (CMDL). Validation was carried out separately for clear-sky and all-sky conditions. For the shortwave, systematic errors varied from −12 to 10 W m−2 for clear skies and from −5 to 35 W m−2 for all-sky conditions. Random errors varied from 20 to 40 W m−2 for clear skies but were much larger (45–85 W m−2) f...

A new 147–56 hPa water vapor product from the UARS Microwave Limb Sounder

Measurements of H2O in the tropopause region have been obtained by production of a new data set from the Microwave Limb Sounder (MLS) on the Upper Atmosphere Research Satellite (UARS). A modified version of the retrieval scheme used to produce upper tropospheric humidity (UTH) from the MLS 203 GHz radiometer was applied to the MLS 183 GHz radiometer measurements to produce useful H2O data at 147, 121, 100, 83, 68, and 56 hPa. These new data, for the first 18 months of the UARS mission when the MLS 183 GHz radiometer was operational, fill an important “gap” around 100 hPa where previous MLS H2O data were generally not useful. Characteristics of the new data set are discussed and compared with National Oceanic and Atmospheric Administration (NOAA), Climate Monitoring and Diagnostics Laboratory (CMDL) frost‐point hygrometer, and UARS Halogen Occultation Experiment (HALOE) measurements.

Calculation of total column ozone from global UV spectra at high latitudes

A new algorithm to retrieve total column ozone from global spectral UV irradiance measurements is presented, and its accuracy is assessed. The expanded uncertainty (coverage factor 2) of the resulting ozone values varies between 2% and 3.5% for solar zenith angles (SZA) smaller than 75° and clear skies. For larger SZA the uncertainty becomes dominated by the sensitivity of the method to the atmospheric ozone distribution. Using this algorithm, ozone values were calculated from UV spectra measured by the National Science Foundation's SUV‐100 spectroradiometer at Barrow, Alaska, between 1996 and 2001. Special attention was given to March–April 2001, the period when the campaign “Total Ozone Measurements by Satellites, Sondes, and Spectrometers at Fairbanks” (TOMS3F) took place. The data set was compared with observations by NASA's Earth Probe Total Ozone Mapping Spectrometer (TOMS) and a Dobson spectrophotometer operated by NOAA's Climate Monitoring and Diagnostics Laboratory (CMDL) at Barrow. On average, the new algorithm generates ozone values in spring 2.2% lower than TOMS observations and 1.8% higher than Dobson measurements. From the uncertainty budget and the comparison with TOMS and Dobson it can be concluded that ozone values retrieved from global UV spectra have a similar accuracy as observations with standard instrumentation used for ozone monitoring. The new data set can therefore be used for validation of other ozone data.

In situ measurements of atmospheric methane at GAGE/AGAGE sites during 1985–2000 and resulting source inferences

Continuous measurements of methane since 1986 at the Global Atmospherics Gases Experiment/Advanced Global Atmospherics Gases Experiment (GAGE/AGAGE) surface sites are described. The precisions range from approximately 10 ppb at Mace Head, Ireland, during GAGE to better than 2 ppb at Cape Grim, Tasmania, during AGAGE (i.e., since 1993). The measurements exhibit good agreement with coincident measurements of air samples from the same locations analyzed by Climate Monitoring and Diagnostics Laboratory (CMDL) except for differences of approximately 5 ppb before 1989 (GAGE lower) and about 4 ppb from 1991 to 1995 (GAGE higher). These results are obtained before applying a factor of 1.0119 to the GAGE/AGAGE values to place them on the Tohoku University scale. The measurements combined with a 12‐box atmospheric model and an assumed atmospheric lifetime of 9.1 years indicates net annual emissions (emissions minus soil sinks) of 545 Tg CH4 with a variability of only ±20 Tg from 1985 to 1997 but an increase in the emissions in 1998 of 37 ± 10 Tg. The effect of OH changes inferred by Prinn et al. [2001] is to increase the estimated methane emissions by approximately 20 Tg in the mid‐1980s and to reduce them by 20 Tg in 1997 and by more thereafter. Using a two‐dimensional (2‐D), 12‐box model with transport constrained by the GAGE/AGAGE chlorofluorocarbon measurements, we calculate that the proportion of the emissions coming from the Northern Hemisphere is between 73 and 81%, depending on the OH distribution used. However, this result includes an adjustment of 5% derived from a simulation of the 2‐D estimation procedure using the 3‐D MOZART model. This adjustment is needed because of the very different spatial emission distributions of the chlorofluorocarbons and methane which makes chlorofluorocarbons derived transport rates inaccurate for the 2‐D simulation of methane. The 2‐D model combined with the annual cycle in OH from Spivakovsky et al. [2000] provide an acceptable fit to the observed 12‐month cycles in methane. The trend in the amplitude of the annual cycle of methane at Cape Grim is used to infer a trend in OH in 30°–90°S of 0 ± 5% per decade from 1985 to 2000, in qualitative agreement with Prinn et al. [2001] for the Southern Hemisphere.

Assimilation of carbon monoxide measured from satellite in a three‐dimensional chemistry‐transport model

Carbon monoxide measurements are obtained from the analysis of the spectra provided by the Interferometric Monitor for Greenhouse Gases (IMG) instrument, which flew on board the Japanese ADEOS satellite. The averaging kernel function of the instrument, which provides the sensitivity of retrieved CO to the vertical atmospheric layers, is calculated. A sequential assimilation approach is used to incorporate this CO data set, along with a detailed associated error budget, into a global three‐dimensional chemistry‐transport model (MOZART version 2). We show how data assimilation allows one to highlight the differences between modeled and observed CO global distribution. Surface CO mixing ratios computed after assimilation of total columns provided by the IMG instrument are compared with the National Oceanic and Atmospheric Administration (NOAA) ‐ Climate Monitoring and Diagnostics Laboratory (CMDL) in situ measurements, and a good agreement is found between the two data sets.

Is the biomass burning source of CO decreasing?

To investigate secular changes in CO and CH4, we examined monthly means of tropospheric measurements made from samples collected at 19 fixed sites in the National Oceanic and Atmospheric Administration (NOAA) Climate Monitoring and Diagnostics Laboratory (CMDL) global cooperative flask sampling network. The CH4 data are available for the period 1984–1995. A somewhat shorter time series is available for CO (1989–1995). The data were analyzed to extract a consistent pattern of change in time and in latitude. The most important preliminary finding is that the patterns of CO and CH4 change appear to resemble that of biomass burning. That is, there is maximum change during local spring in both northern and southern hemispheres. If we attribute a significant part of the change in CH4 trend (3–6 ppb/yr) to biomass burning, the corresponding change in CO is approximately 2–5 ppb/yr. This would explain the bulk of the observed change in CO (4–7 ppb/yr).

In situ CO concentrations at the sites Zugspitze (47°N, 11°E) and Cape Point (34°S, 18°E) in April and October 1994

Continuous measurements of CO have been performed at the coastal site Cape Point (34°S, 18°E) and at the continental mountain site Zugspitze (47°N, 11°E) since 1978 and 1990, respectively. The CO concentrations observed at both stations in 1994 during the periods April 9–18, and September 30 to October 10 were studied in detail with the aim to supplement CO observations from space made by NASA during two shuttle flights (measurement of air pollution from satellites (MAPS) project). All CO values reported were adjusted to the NOAA Climate Monitoring and Diagnostics Laboratory (CMDL) calibration scale. CO mixing ratios at Cape Point comprised episodes of baseline CO levels in maritime air (average: 48.8 ppb (April); 69.4 ppb (September/October)) and of elevated levels related to continental air and regional pollution (average: 89.5 ppb (April); 102.1 ppb (September/‐October)). During the same periods the mean CO mixing ratio at the Zugspitze amounted to 220.1 ppb (range 150 ‐ 358 ppb) and 124.8 ppb (range 78–175 ppb), respectively. Due to the prevailing airflow, CO levels at the Zugspitze were unusually high compared to the long‐term average during the April mission (time of seasonal maximum). In contrast, they were close to the average during the October mission. Baseline concentrations at Cape Point were about 3–4 ppb above the long‐term average for both April (increasing side of seasonal cycle) and October (time of seasonal maximum), which is within the range of normal interannual variability. A preliminary comparison with the MAPS data for the respective geographic regions showed good agreement of the CO mixing ratios for clean air at Cape Point in April and at the Zugspitze in October. In addition, the CO levels observed in continental air at Cape Point in October agreed well with the MAPS data. Obvious differences in CO concentrations for other parts of the records mainly reflected uncomparable atmospheric conditions. In particular, they seemed to be related to either vertical gradients of CO or small‐scale differences in air mass composition as indicated by meteorological analyses.

Atmospheric methane measurements in central New England: An analysis of the long‐term trend and the seasonal and diurnal cycles

We have compiled a unique high‐resolution ambient‐air methane data set consisting of approximately 125,000 independently measured data points for the years 1991–1995 that have been collected at a site in the northeastern United States. The annual median mixing ratio of methane for all measurements was 1808 ppbv in 1992, increasing at a variable rate to 1837 ppbv in 1995. The lower 10–30% of the data from each month were defined as representative of background air and were compared with the global Climate Monitoring and Diagnostics Laboratory (CMDL) data set. The background data exhibit a variable upward trend of 5.5 ± 2 ppbv/yr during the 4‐year time period, with most of the increase observed during 1993 and 1994. The seasonal cycle for the background data set is similar to what is observed by CMDL stations and varies from 24 to 35 ppbv. The amplitude of the seasonal cycle for the full data set was larger, ranging from 35 to 44 ppbv. Differences between the full and background mixing ratios vary on a seasonal basis and are largest in the winter and smallest in the summer. These differences appear to be controlled by changes in atmospheric stability and changes in emissions from local and regional sources throughout the year. Diurnal cycles exist in the data, with the magnitude and timing of maximum and minimum values being controlled by inputs from local sources and atmospheric stability. Nearby wetlands contribute to an overnight buildup of methane in the late spring and summer. The magnitude of the daily cycle is largest in July and August (∼23 ppbv), when inputs from wetlands are large and wind speed is generally low. In April, the daily cycle is smallest (∼6 ppbv), when inputs from local sources are low and more vigorous atmospheric mixing limits pollution buildup.

Gravimetric preparation of gas phase working standards containing volatile halogenated compounds for oceanographic applications

Gas phase standards, containing CCl 3F (CFC-11), CCl 2F 2 (CFC-12), CCl 2FCClF 2 (CFC-113), CH 3CCl 3 and CCl 4 in the pmol mol −1 range, were prepared gravimetrically in dry N 2. The standards were prepared with the relative ratios of the various compounds close to those found in seawater, to facilitate calibration of oceanic halocarbon measurements. The standards made in this study were intercalibrated against an atmospheric-ratio-based standard that was analyzed at both Scripps Institution of Oceanography (SIO) and NOAA's Climate Monitoring and Diagnostics Laboratory (CMDL). A total of 21 standards was made, with the concentrations of the above halocarbons reported on both the CMDL and SIO 1993 scales. These standards are currently being used by ten different research groups making oceanic halocarbon measurements. The average systematic deviation of all compounds in our standards was generally ± 5% or less from the SIO 1993 and CMDL scales. Deviations for CH 3CCl 3 between our standards and the CMDL scale were slightly larger, with our standards, on average, approximately 10% lower.

Partial picture of methyl bromide demands more pieces

Consider the vast area and volume of the Earth's oceans as a large reservoir that produces, removes, and, to some degree, regulates gases—including some ozone‐eating chemicals released into the atmosphere by human activities. New modeling studies based on recent monitoring data suggest such a picture, with the oceans taking from the atmosphere more methyl bromide, a source of ozone‐destroying bromine, than previously thought. This rapid removal by the ocean shortens the average estimated lifetime of methyl bromide to just 0.7 of a year— much briefer than its former calculated lifetime of 2 years.“Measurements show that in most of the oceans, methyl bromide is undersaturated, which suggests that sinks outweigh sources in the water,” said James Butler, coauthor of the modeling study, which appeared in the May 15 issue of Geophysical Research Letters. Butler, of NOAA's Climate Monitoring and Diagnostics Laboratory (CMDL) in Boulder, and Shari Yvon‐Lewis, of the University of Colorado, used latitude‐dependent degradation rate constants based on monitoring data to model methyl bromide flux between the atmosphere and ocean. They found that the undersaturation of methyl bromide in the ocean requires a great deal more degradation than chemical reactions alone could accomplish.

Comparison of STOIC 1989 ground‐based lidar, microwave spectrometer, and Dobson spectrophotometer Umkehr ozone profiles with ozone profiles from balloon‐borne electrochemical concentration cell ozonesondes

Ground‐based measurements of stratospheric ozone using a Jet Propulsion Laboratory (JPL) lidar, a NASA Goddard Space Flight Center (GSFC) lidar, a Millitech Corporation/NASA Langley Research Center (Millitech/LaRC) microwave spectrometer, and a NOAA Dobson ozone spectrophotometer were compared with in situ measurements made quasi‐simultaneously with balloon‐borne electrochemical concentration cell (ECC) ozonesondes during 10 days of the Stratospheric Ozone Intercomparison Campaign (STOIC). The campaign was conducted at Table Mountain Observatory, California, during the summer of 1989. ECC ozonesondes were flown by NOAA Climate Monitoring and Diagnostics Laboratory (CMDL) personnel as well as by personnel from the NASA Wallops Island Flight Facility (WFF). Within the altitude range of 20–32 km, ozone measurement precisions were estimated to be ±0.6 to ±1.2% for the JPL lidar, ±0.7% for the GSFC lidar, ±4% for the microwave spectrometer, and ±3% for the NOAA ECC ozonesonde instruments. These precisions decreased in the 32 to 38.6‐km altitude range to ±1.3, ±1.5, and ±3% to ±10% for the JPL lidar, GSFC lidar, and the ECC sondes, respectively, but remained at ±4% for the microwave instrument. Ozone measurement accuracies in the 20 to 32 km altitude range were estimated to be ±1.2 to ±2.4% for the JPL lidar, ±1.4% for the GSFC lidar, ±6% for the microwave radiometer, and ±5% for the ECC ozonesondes. The accuracies decreased in the 32 to 38.6‐km altitude range to ±2.6, ±3.0, ±7, and 1 ± 4% to −4 ± 10% for the JPL lidar, the GSFC lidar, the microwave spectrometer, and the ECC ozonesondes, respectively. While accuracy estimates for the ECC sondes were obtained by combining random and estimated bias errors, the accuracies for the lidar instruments were obtained by doubling the measurement precision figures, with the assumption that such doubling accounts for systematic errors. Within the altitude range of 20–36 km the mean ozone profiles produced by the JPL, GSFC, and the Millitech/LaRC groups did not differ from the mean ECC sonde ozone profile by more than about 2, 4, and 5%, respectively. Six morning Dobson instrument Umkehr observations yielded mean ozone amounts in layers 3 and 5–7 that agreed with comparison ECC ozonesonde data to within ±4%. In layer 4 the difference was 7.8%. (Less favorable comparison data were obtained for six afternoon Umkehr observations made in highly polluted near‐surface air.) This good agreement in overall results obtained lends credence to the reliability of the ozone measurements made at Table Mountain Observatory during STOIC 1989.

Aerosol absorption measurements at Barrow, Mauna Loa and the south pole

Aerosol absorption (σap) has been measured continuously using aethalometers at Barrow, Alaska (1986 to present); Mauna Loa, Hawaii (1990 to present); and south pole, Antarctica (1987–1990). These three stations are part of a network of baseline monitoring stations operated by the Climate Monitoring and Diagnostics Laboratory (CMDL) of the National Oceanic and Atmospheric Administration (NOAA). Condensation nucleus (CN) concentration and multiwavelength aerosol scattering (σsp) have also been measured continuously for many years at these stations. Aethalometer measurements are usually reported in terms of atmospheric black carbon aerosol (BC) concentration using the calibration suggested by the manufacturer. Here we deduce the in situ σap(550 nm) from aethalometer measurements by assuming that the aerosol absorption on the aethalometer filter is enhanced by a factor of 1.9 over that in the atmosphere. This is consistent with using 19 m2 g−1 for the specific absorption of BC on the aethalometer filter and 10 m2 g−1 for the in situ specific absorption of BC in the atmosphere (the ratio of the two specific absorptions is 1.9). Although these values of specific absorption may vary significantly for different environments, the ratio might be expected to be relatively constant. The single‐scattering albedo, defined by ω = σsp/(σsp + σap), has been estimated from the simultaneous measurements of σap and σsp. Furthermore, assuming a 1/λ dependence for σap in the 450 to 700‐nm wavelength region, multiwavelength σsp measurements allow the estimation of the wavelength dependence of ω. Each station shows a considerable annual cycle in σap, σsp, and ω. The maximum in the Barrow annual cycle is caused primarily by the springtime Arctic haze phenomenon; the maximum in the Mauna Loa annual cycle is caused by the springtime Asian dust transport; and the maximum in the south pole annual cycle is caused by late winter transport from southern midlatitudes. It was found that annual mean values are σap = 4.1 × 10−7 m−1 (≈41 ng m−3 BC) and ω = 0.96 for Barrow; σap = 5.8 × 10−8 m−1 (≈5.8 ng m−3 BC) and ω = 0.97 for Mauna Loa; and σap = 6.5 × 10 −9 m−1 (≈0.65 ng m−3 BC) and ω = 0.97 for south pole. It was also found that the wavelength dependence of ω may be important at Barrow and south pole, but not important at Mauna Loa.

On the frequency of long-range transport events at point barrow, Alaska, 1983–1992

The Point Barrow, Alaska pollutant and meteorological data bases from the Climate Monitoring and Diagnostics Laboratory (CMDL) baseline station are evaluated for the first 120 days of each year between 1983 and 1992. The purpose of this study is to investigate whether a relationship between gaseous and aerosol pollutants during clean sector winds could be used to indicate periods of long-range transport of pollutants. Representative pollutant parameters used include carbon dioxide and aerosol light scattering ( σ sp), with methane, condensation nuclei, and black carbon used in support. Several interesting relationships emerge between the gases and σ sp during long-range transport events: (1) the frequency of clean sector winds for most months is greater than 70%, with the range 31.6–92.8%; (2) high correlations between CO 2 and σ sp do not necessarily occur during long-range transport events, and the relationship between the two parameters is weak and erratic; (3) a considerable majority of transport periods occur in January and March, with the highest frequency in the AGASP measurement years 1983 and 1986, in some contrast to previous analysis using only haze as the pollution indicator; (4) pollution reaching surface monitors at Point Barrow most often originates from pooled air in the Arctic Basin, with no clear definition of more distant source regions.