Showing papers by "Climate Monitoring and Diagnostics Laboratory published in 2002"

A 3‐year record of simultaneously measured aerosol chemical and optical properties at Barrow, Alaska

Abstract: [1] Results are presented from 3 years of simultaneous measurements of aerosol chemical composition and light scattering and absorption at Barrow, Alaska. All results are reported at the measurement relative humidity of ≤ 40%. Reported are the annual cycles of the concentration of aerosol mass, sea salt, non-sea-salt (nss) sulfate, methanesulfonate or MSA−, NH4+, and nss K+, Mg+2, and Ca+2 for the submicron and supermicron size ranges. Submicron nss SO4=, NH4+, and nss K+, Mg+2, and Ca+2 peak in winter and early spring corresponding to the arrival and persistence of Arctic Haze. Submicron sea salt displays a similar annual cycle presumably due to long-range transport from the northern Pacific Ocean. Supermicron sea salt peaks in summer corresponding to a decrease in sea ice extent. Submicron and supermicron MSA− peak in the summer due to a seasonal increase in the flux of dimethylsulfide from the ocean to the atmosphere. A correlation of MSA− and particle number concentrations suggests that summertime particle production is associated with this biogenic sulfur. Mass fractions of the dominant chemical species were calculated from the concentrations of aerosol mass and chemical species. For the submicron size range the ionic mass and associated water make up 80 to 90% of the aerosol mass from November to May. Of this ionic mass, sea salt and nss SO4= are the dominant species. The residual mass fraction, or fraction of mass that is chemically unanalyzed, is equivalent to the ionic mass fraction in June through October. For the supermicron size range the ionic mass and associated water make up 60 to 80% of the aerosol mass throughout the year with sea salt being the dominant species. Also reported for the submicron size range are the annual cycles of aerosol light scattering and absorption at 550 nm, Angstrom exponent for the 450 and 700 nm wavelength pair, and single scattering albedo at 550 nm. On the basis of linear regressions between the concentrations of sea salt and nss SO4= and the light scattering coefficient, sea salt has a dominant role in controlling light scattering during the winter, nss SO4= is dominant in the spring, and both components contribute to scattering in the summer. Submicron mass scattering efficiencies of the dominant aerosol chemical components (nss SO4=, sea salt, and residual mass) were calculated from a multiple linear regression of the measured light scattering versus the component concentrations. Submicron nss SO4= mass scattering efficiencies were relatively constant throughout the year with seasonal averages ranging from 4.1 ± 2.9 to 5.8 ± 1.0 m2 g−1. Seasonal averages for submicron sea salt ranged from 1.8 ± 0.37 to 5.1 ± 0.97 m2 g−1 and for the residual mass ranged from 0.21 ± 0.31 to 1.5 ± 1.0 m2 g−1. Finally, concentrations of nss SO4= measured at Barrow were compared to those measured at Poker Flat Rocket Range, Denali National Park, and Homer for the 1997/1998 and 1998/1999 Arctic Haze seasons. Concentrations were highest at Barrow and decreased with latitude from Poker Flat to Denali to Homer revealing a north to south gradient in the extent of the haze.

Variability of Aerosol Optical Properties at Four North American Surface Monitoring Sites

Abstract: Aerosol optical properties measured over several years at surface monitoring stations located at Bondville, Illinois (BND); Lamont, Oklahoma (SGP); Sable Island, Nova Scotia (WSA); and Barrow, Alaska (BRW), have been analyzed to determine the importance of the variability in aerosol optical properties to direct aerosol radiative forcing calculations. The amount of aerosol present is of primary importance and the aerosol optical properties are of secondary importance to direct aerosol radiative forcing calculations. The mean aerosol light absorption coefficient (σap) is 10 times larger and the mean aerosol scattering coefficient (σsp) is 5 times larger at the anthropogenically influenced site at BND than at BRW. The aerosol optical properties of single scattering albedo (ωo) and hemispheric backscatter fraction (b) have variability of approximately ± 3% and ± 8%, respectively, in mean values among the four stations. To assess the importance of the variability in ωo and b on top of the atmosphere a...

Emissions of carbon dioxide, carbon monoxide, and methane from boreal forest fires in 1998

Abstract: The global boreal forest region experienced some 17.9 million ha of fire in 1998, which could be the highest level of the decade. Through the analysis of fire statistics from North America and satellite data from Russia, semimonthly estimates of area burned for five different regions in the boreal forest were generated and used to estimate total carbon release and CO 2 , CO, and CH 4 emissions. Different levels of biomass, as well as different biomass categories, were considered for each of the five different regions (including peatlands in the Russian Far East and steppes in Siberia), as were different levels of fraction of biomass (carbon) consumed during fires. Finally, two levels of flaming versus smoldering combustion were considered in the model. Boreal forest fire emissions for 1998 were estimated to be 290-383 Tg of total carbon, 828-1103 Tg of CO 2 , 88-128 Tg of CO, and 2.9-4.7 Tg of CH 4 . The higher estimate represents 8.9% of total global carbon emissions from biomass burning, 13.8% of global fire CO emissions, and 12.4% of global fire CH4 emissions. Russian fires accounted for 71% of the total emissions, with the remainder (29%) from fires in North America. Assumptions regarding the level of smoldering versus flaming generally resulted in small (<4%) variations into the emissions estimates, although in two cases, these variations were higher (6% and 12%). We. estimated that peatland fires in the Russian Far East contributed up to 40 Tg of carbon to the atmosphere in the fall of 1998. The combined seasonal CO emissions from forest and peatland fires in Russia are consistent with anomalously high atmospheric CO measurements collected at Point Barrow, Alaska.

Carbonaceous aerosols over the Indian Ocean during the Indian Ocean Experiment (INDOEX): Chemical characterization, optical properties, and probable sources

Abstract: components) of fine-mode particles in these layers was 153 ± 79 m gm � 3 The major components were particulate organic matter (POM, 35%), SO4� (34%), black carbon (BC, 14%), and NH4 + (11%) The main difference between the composition of the marine boundary layer (MBL, 0 to � 12 km), and the overlying residual continental boundary layer (12 to � 32 km) was a higher abundance of SO4 2� relative to POM in the MBL, probably due to a faster conversion of SO2 into SO4 2� in the MBL Our results show that carbon is a major, and sometimes dominant, contributor to the aerosol mass and that its contribution increases with altitude Low variability was observed in the optical properties of the aerosol in the two layers Regression analysis of the absorption coefficient at 565 nm on BC mass (BC < 40 m gCm � 3 ) yielded a specific absorption cross section of 81 ± 07 m 2 g � 1 for the whole period The unusually high fraction of BC and the good correlation between the absorption coefficient and BC suggest that BC was responsible for the strong light absorption observed for the polluted layers during INDOEX High correlation between BC and total carbon (TC) (r 2 = 086) suggest that TC is predominantly of primary origin Good correlations were also found between the scattering coefficient at 550 nm and the estimated aerosol mass for the fine fraction These yielded a specific scattering cross section of 49 ± 04 m 2 g � 1 The observed BC/TC, BC/OC, SO4� /BC, and K + /BC ratios were fairly constant throughout the period These ratios suggest that between 60 and 80% of the aerosol in the polluted layers during INDOEX originated from fossil fuel and between 20 and 40% from biofuel combustion INDEX TERMS: 0305 Atmospheric Composition and Structure: Aerosols and particles (0345, 4801); 0322 Atmospheric Composition and Structure: Constituent sources and sinks; 0345 Atmospheric Composition and Structure: Pollution—urban and regional (0305); 0365 Atmospheric Composition and Structure: Troposphere—composition and chemistry; 4801 Oceanography: Biological and Chemical: Aerosols (0305); KEYWORDS: carbonaceous aerosols; INDOEX; chemical characterization; optical properties; sources; aerosols

Aerosol optical properties during INDOEX 1999: Means, variability, and controlling factors

Abstract: [1] As part of the Indian Ocean Experiment (INDOEX) 1999 Intensive Field Phase, measurements of aerosol properties were made on board the R/V Ronald H. Brown in the Indian Ocean north and south of the Intertropical Convergence Zone (ITCZ) in the Arabian Sea and in the Bay of Bengal. On the basis of air mass trajectories, eight air mass source regions were identified including the southern hemisphere Atlantic; southern hemisphere Indian Ocean; northern hemisphere Indian Ocean; east Indian subcontinent where trajectories came from near Calcutta, through the southern portion of India, and then to the ship; Indian subcontinent where trajectories came from across central India to the ship; Arabia; Arabia/Indian subcontinent, a mixed region where lower-level trajectories came from Arabia and upper-level trajectories came from India; and Arabian Sea/coastal India where trajectories came from along the coast of India to the ship. Properties of the aerosol measured in the marine boundary layer included chemical composition, number size distribution, and scattering and absorption coefficients. In addition, vertical profiles of aerosol backscatter and optical depth were measured. Presented here as a function of air mass source region are the concentrations and mass fractions of the dominant aerosol chemical components, the fraction of the extinction measured at the surface due to each component, mass extinction efficiencies of the individual components, aerosol scattering and absorption coefficients, single scattering albedo, Angstrom exponent, and optical depth. All results except aerosol optical depth are reported at the measurement relative humidity of 55 ± 5%. For air masses that originated from the two southern hemisphere marine regions (southern hemisphere Atlantic and Indian Ocean), sea salt dominated the extinction by sub-1 μm and sub-10 μm aerosol particles. The ratios of sub-1μm to sub-10 μm extinction were the lowest measured of all air mass source regions (mean values of 28 and 40%) due to the dominance of the aerosol mass by supermicron sea salt. In addition, aerosol optical depths were the lowest measured averaging 0.06 ± 0.03. Non-sea-salt (nss) sulfate aerosol concentrations in air masses from the northern hemisphere Indian Ocean were a factor of 6 higher than those in southern hemisphere air masses, while submicron sea-salt concentrations were comparable. Sulfate aerosol made up 40% of the sub-1μm extinction, while sea salt dominated the sub-10 μm extinction. Aerosol optical depths for this source region averaged 0.10 ± 0.03. A mean single scattering albedo near 0.89 and detectable black carbon (BC) concentrations (0.14 ± 0.05 μg m−3) indicated the transport of continentally derived aerosol to the ITCZ. The two regions influenced by low-level (500 m) airflow from Arabia had higher concentrations of submicron nss sulfate, particulate organic matter (POM), and inorganic oxidized material (IOM) than were observed in the marine regions. Concentrations of supermicron IOM were comparable to supermicron sea-salt concentrations. Nss sulfate aerosol dominated the sub-1 μm extinction and made significant contributions to the sub-10 μm extinction. Sea salt dominated the supermicron extinction. Mean BC contributions to submicron extinction were 8 and 12%. Single scattering albedo values averaged 0.93 ± 0.02 and 0.89 ± 0.02 for these two source regions. Aerosol optical depths averaged 0.19 ± 0.12 and 0.38 ± 0.07 with the higher value due to upper-level (2500 m) flow from India. Regions influenced by low-level airflow from the Indian subcontinent had the highest submicron nss sulfate, POM, BC, and IOM concentrations measured during the experiment. Supermicron sea-salt concentrations were lower than or comparable to supermicron nitrate concentrations. Sub-1 μm and sub-10 μm extinction were dominated by nss sulfate aerosol although a burning component consisting of BC, KNO3, and K2SO4 made a nearly equivalent contribution. These regions had a mean single scattering albedo of 0.85 ± 0.01, the lowest measured for any region. Mean aerosol optical depths were highest (0.3 to 0.4) for regions with low-level or upper-level airflow from the Indian subcontinent.

Methyl iodide: Atmospheric budget and use as a tracer of marine convection in global models

Abstract: biomass burning are also included in the model. The model captures 40% of the variance in the observed seawater CH3I(aq) concentrations. Simulated concentrations at midlatitudes in summer are too high, perhaps because of a missing biological sink of CH3I(aq). We define a marine convection index (MCI) as the ratio of upper tropospheric (8–12 km) to lower tropospheric (0–2.5 km) CH3I concentrations averaged over coherent oceanic regions. The MCI in the observations ranges from 0.11 over strongly subsiding regions (southeastern subtropical Pacific) to 0.40 over strongly upwelling regions (western equatorial Pacific). The model reproduces the observed MCI with no significant global bias (offset of only +11%) but accounts for only 15% of its spatial and seasonal variance. The MCI can be used to test marine convection in global models, complementing the use of radon-222 as a test of continental convection. INDEX TERMS: 0312 Atmospheric Composition and Structure: Air/sea constituent fluxes (3339, 4504); 0322 Atmospheric Composition and Structure: Constituent sources and sinks; 0368 Atmospheric Composition and Structure: Troposphere—constituent transport and chemistry; KEYWORDS: methyl iodide, marine convection, atmospheric tracer, global budget of methyl iodide

Sources of tropospheric ozone along the Asian Pacific Rim: An analysis of ozonesonde observations

Abstract: The sources contributing to tropospheric ozone over the Asian Pacific Rim in different seasons are quantified by analysis of Hong Kong and Japanese ozonesonde observations with a global three-dimensional (3-D) chemical transport model (GEOS-CHEM) driven by assimilated meteorological observations. Particular focus is placed on the extensive observations available from Hong Kong in 1996. In the middle-upper troposphere (MT- UT), maximum Asian pollution influence along the Pacific Rim occurs in summer, reflecting rapid convective transport of surface pollution. In the lower troposphere (LT) the season of maximum Asian pollution influence shifts to summer at midlatitudes from fall at low latitudes due to monsoonal influence. The UT ozone minimum and high variability observed over Hong Kong in winter reflects frequent tropical intrusions alternating with stratospheric intrusions. Asian biomass burning makes a major contribution to ozone at less than 32 deg.N in spring. Maximum European pollution influence (less than 5 ppbv) occurs in spring in the LT. North American pollution influence exceeds European influence in the UT-MT, reflecting the uplift from convection and the warm conveyor belts over the eastern seaboard of North America. African outflow makes a major contribution to ozone in the low-latitude MT-UT over the Pacific Rim during November- April. Lightning influence over the Pacific Rim is minimum in summer due to westward UT transport at low latitudes associated with the Tibetan anticyclone. The Asian outflow flux of ozone to the Pacific is maximum in spring and fall and includes a major contribution from Asian anthropogenic sources year-round.

Development of analytical methods and measurements of 13C/12C in atmospheric CH4 from the NOAA Climate Monitoring and Diagnostics Laboratory Global Air Sampling Network

Abstract: [1] 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 (δ13CH4) 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 δ13CH4 through the NOAA Climate Monitoring and Diagnostics Laboratory Cooperative Air Sampling Network. We then present a record of δ13CH4 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 δ13C 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 δ13C and CH4 mole fraction measurements can constrain broad categories of source emissions. We find that the biggest sources of error are not the atmospheric δ13C measurements but instead the radiocarbon-derived fossil fuel emission estimates, rate coefficients for methane destruction, and isotopic ratios of source emissions.

Top-down estimate of a large source of atmospheric carbon monoxide associated with fuel combustion in Asia

Abstract: [1] Deriving robust regional estimates of the sources of chemically and radiatively important gases and aerosols to the atmosphere is challenging. Here, we focus on carbon monoxide. Using an inverse modeling methodology, we find that the source of carbon monoxide from fossil-fuel and biofuel combustion in Asia during 1994 was 350–380 Tg yr−1, which is 110–140 Tg yr−1 higher than bottom-up estimates derived using traditional inventory-based approaches. This discrepancy points to an important gap in our understanding of the human impact on atmospheric chemical composition.

Balloon-borne observations of water vapor and ozone in the tropical upper troposphere and lower stratosphere

Abstract: [1] Balloon-borne observations of frost-point temperature and ozone in the equatorial western, central and eastern Pacific as well as over equatorial eastern Brazil provide a highly accurate data set of water vapor across the tropical tropopause. Data were obtained at San Cristobal, Galapagos, Ecuador (0.9°S, 89.6°W), during the late northern winter and the late northern summer in 1998 and 1999 and at Juazeiro do Norte, Brazil (7.2°S, 39.3°W), in February and November 1997. Earlier data in the western Pacific region in March 1993 were reanalyzed to extend the scope of the observations. The data show three different circumstances in which saturation or supersaturation occurs and imply different mechanisms for dehydration at the tropical tropopause: (1) convective dehydration, (2) slow-ascent dehydration, and (3) large-scale wave-driven dehydration. Furthermore, air that crosses the tropical tropopause in the late northern summer may be dehydrated further during late northern fall, as the average tropical tropopause rises and cools. Not all soundings show dehydration, and there are clear differences in the frequency and depth of saturation in different regions and seasons. The tropopause transition region can be identified in accurate measurements of relative humidity, even under conditions where ozone observations are ambiguous. Deep convection plays an important role in setting up this transition region, which is then subject to large-scale wave activity and wave breaking at the tropopause or midlatitude intrusions. High relative humidities over regions of strong subsidence show that descending motion in the troposphere is limited to levels below the transition region.

Carbon isotope discrimination of arctic and boreal biomes inferred from remote atmospheric measurements and a biosphere-atmosphere model

Abstract: Estimating discrimination against ^(13)C during photosynthesis at landscape, regional, and biome scales is difficult because of large-scale variability in plant stress, vegetation composition, and photosynthetic pathway. Here we present estimates of ^(13)C discrimination for northern biomes based on a biosphere-atmosphere model and on National Oceanic and Atmospheric Administration Climate Monitoring and Diagnostics Laboratory and Institute of Arctic and Alpine Research remote flask measurements. With our inversion approach, we solved for three ecophysiological parameters of the northern biosphere (^(13)C discrimination, a net primary production light use efficiency, and a temperature sensitivity of heterotrophic respiration (a Q10 factor)) that provided a best fit between modeled and observed δ^(13)C and CO_2. In our analysis we attempted to explicitly correct for fossil fuel emissions, remote C4 ecosystem fluxes, ocean exchange, and isotopic disequilibria of terrestrial heterotrophic respiration caused by the Suess effect. We obtained a photosynthetic discrimination for arctic and boreal biomes between 19.0 and 19.6‰. Our inversion analysis suggests that Q10 and light use efficiency values that minimize the cost function covary. The optimal light use efficiency was 0.47 gC MJ^(−1) photosynthetically active radiation, and the optimal Q10 value was 1.52. Fossil fuel and ocean exchange contributed proportionally more to month-to-month changes in the atmospheric growth rate of δ^(13)C and CO_2 during winter months, suggesting that remote atmospheric observations during the summer may yield more precise estimates of the isotopic composition of the biosphere.

Simulation of ozone depletion in spring 2000 with the Chemical Lagrangian Model of the Stratosphere (CLaMS)

Abstract: [1] Simulations of the development of the chemical composition of the Arctic stratosphere for spring 2000 are made with the Chemical Lagrangian Model of the Stratosphere (CLaMS). The simulations are performed for the entire Northern Hemisphere on four isentropic levels (400–475 K). The initialization in early February is based on observations made from satellite, balloon and ER-2 aircraft platforms. Tracer-tracer correlations from balloon-borne cryosampler (Triple) and ER-2 measurements, as well as tracer-PV correlations, are used to derive a comprehensive hemispherical initialization of all relevant chemical trace species. Since significant denitrification has been observed on the ER-2 flights, a parameterization of the denitrification is derived from NOy and N2O observations on board the ER-2 aircraft and the temperature history of the air masses under consideration. Over the simulation period from 10 February to 20 March, a chemical ozone depletion of up to 60% was derived for 425–450 K potential temperature. Maximum vortex-averaged chemical ozone loss rates of 50 ppb d−1 or 4 ppb per sunlight hour were simulated in early March 2000 at the 425 and 450 K potential temperature levels. We show comparisons between the measurements and the simulations for the location of the ER-2 flight paths in late February and March and the location of the Triple balloon flight. The simulated tracer mixing ratios are in good agreement with the measurements. It was not possible to reproduce the exact details of the inorganic chlorine compounds. The simulation agrees with ClOx observations on the Triple balloon flight but overestimates for the ER-2 flights. The simulated ozone depletion agrees with estimates from other observations in the 425 and 450 K levels, but is underestimated on the 475 K level.

Lidar validation of SAGE II aerosol measurements after the 1991 Mount Pinatubo eruption

Abstract: [1] After the Mount Pinatubo volcanic eruption on 15 June 1991 the Stratospheric Aerosol and Gas Experiment (SAGE) II instrument made extensive aerosol extinction retrievals using the limb-viewing technique. In regions of high-aerosol loading, SAGE II was not able to make measurements, resulting in large information gaps both in latitudinal and in longitudinal coverage as well as in the vertical. Here we examine the possibility of filling the vertical gaps using lidar data. We compare every coincident backscattering measurement (at a wavelength of 0.694 μm) from two lidars, at Mauna Loa, Hawaii (19.5°N, 155.6°W), and at Hampton Virginia (37.1°N, 76.3°W), for the 2-year period after the Pinatubo eruption with the SAGE II version 6.0 extinctions at 0.525 and 1.02 μm wavelengths. This is the most comprehensive comparison ever of lidar data with satellite data for the Pinatubo period. We convert backscattering to extinction at the above wavelengths. At altitudes and times with coincident coverage, the SAGE II extinction measurements agree well with the lidar data but less so during the first six months after the eruption, due to the heterogeneity of the aerosol cloud. This shows that lidar data can be combined with satellite data to give an improved stratospheric aerosol data set.

Global tracer modeling during SOLVE: High‐latitude descent and mixing

Abstract: [1] We compare tracer observations made during the northern winter of 1999/2000 with the results of simulations with a three-dimensional chemical transport model, driven by assimilated winds. During the course of the winter, very low concentrations of tracers of tropospheric origin (such as N2O) descend into the lower stratosphere within the polar vortex. The altitude of origin of this air has been a matter of debate in the literature; by midwinter, both observations and model results indicate a significant fraction of mesospheric air in the lower stratosphere. Observations from aircraft and balloon flights reveal markers of mesospheric air within the Arctic vortex in the lower and middle stratosphere. An artificial tracer introduced into the model mesosphere at the start of winter descends (being diluted as it does so) all the way down to the 450 K potential temperature surface by March. Modeled tracer-tracer relationships evolve through the winter in a way similar to observations, but the separation between vortex and extravortex curves is exaggerated, suggesting that the model exhibits excessive horizontal mixing within and into the vortex. The tracer-tracer relationships are used to identify partly mixed air as lying, in tracer-tracer space, in a region intermediate between the characteristic vortex and midlatitude relationships. Air lying in a collar region just inside the vortex edge is thus identified as being mixed, and this indicates excessive horizontal mixing in the model across the vortex edge. INDEX TERMS: 0341 Atmospheric Composition and Structure: Middle atmosphere—constituent transport and chemistry (3334); 3334 Meteorology and Atmospheric Dynamics: Middle atmosphere dynamics (0341, 0342); KEYWORDS: stratosphere, polar vortex, tracer modeling, stratospheric tracers

An intercomparison of aerosol light extinction and 180° backscatter as derived using in situ instruments and Raman lidar during the INDOEX field campaign

Abstract: [1] Aircraft in situ and Raman lidar profiles of aerosol light extinction (ep) and 180 backscattering (p) are compared for 6 days during the Indian Ocean Experiment (INDOEX). The measurements of ep and p were made from the National Center for Atmospheric Research C-130 aircraft using two integrating nephelometers to measure light scattering and one Radiance Research Particle Soot Absorption Photometer to measure light absorption. Particulate 180 backscattering was measured in situ using a new instrument, the 180 backscatter nephelometer. The Institute for Tropospheric Research Raman lidar was located on the island of Hulule (4.18N, 73.53E), and all of the in situ profiles presented are from descents into the Hulule airport. Aerosol optical depth was also measured from Hulule using a Sun photometer, and these data are included in the intercomparison. On average, the lidar-derived values of ep and p are 30% larger than the in situ-derived values to a 95% confidence interval. Possible reasons for the overall discrepancy are (1) a low bias in the in situ measurements because of losses in the C-130 Community Aerosol Inlet; (2) underestimation of the humidification effect on light extinction in the in situ measurements; (3) overestimation of ep and p in the lidar because of subvisible cloud contamination; (4) errors in data processing that could be biasing either measurement, though the lidar retrievals are especially sensitive to this type of error. Temporal and spatial variability also appear to be the source of at least some of the discrepancy in two of the six cases, none of which are well collocated. INDEX TERMS: 0305 Atmospheric Composition and Structure: Aerosols and particles (0345, 4801); 0394 Atmospheric Composition and Structure: Instruments and techniques; 0360 Atmospheric Composition and Structure: Transmission and scattering of radiation; 0345 Atmospheric Composition and Structure: Pollutionurban and regional (0305); KEYWORDS: aersol, optical, lidar, in situ, comparison, INDOEX

Predicting oceanic methyl bromide saturation from SST

Abstract: [1] Data collected from the North Pacific Ocean during September and October 1999 were combined with data from other cruises to assess seasonal differences in the relationships between sea surface temperature (SST) and methyl bromide (CH3Br) saturation. We now are able to reproduce observed saturation anomalies substantially better with the revised, seasonal CH3Br-SST equations than with those that were independent of season. The effect is most noticeable in temperate waters where data combined on an annual basis proved insufficient. The estimated, net global air-sea flux of CH3Br remains negative at −10 to −18 Gg yr−1, which is consistent with extrapolations from observations.

Land use effects on atmospheric 13C imply a sizable terrestrial CO2 sink in tropical latitudes

Abstract: Records of atmospheric CO2 and 13-CO2, can be used to distinguish terrestrial vs. oceanic exchanges of CO2 with the atmosphere. However, this approach has proven difficult in the tropics, partly due to extensive land conversion from C-3 to C-4 vegetation. We estimated the effects of such conversion on biosphere-atmosphere C-13 exchange for 1991 through 1999, and then explored how this 'land-use disequilibrium' altered the partitioning of net atmospheric CO2 exchanges between ocean and land using NOAA-CMDL data and a 2D, zonally averaged atmospheric transport model. Our results show sizable CO2 uptake in C-3-dominated tropical regions in seven of the nine years; 1997 and 1998, which included a strong ENSO event, are near neutral. Since these fluxes include any deforestation source, our findings imply either that such sources are smaller than previously estimated, and/or the existence of a large terrestrial CO2 sink in equatorial latitudes.

Defining the polar vortex edge from an N2O:potential temperature correlation

Abstract: A prerequisite to studying phenomena in the winter stratospheric polar vortex is the separation of measurements inside and outside the dynamical barrier of the vortex edge. We describe a technique to accurately determine the inner edge of the vortex boundary region from measurements of potential temperature and a trace gas, such as N2O, and apply it to in situ aircraft and balloon measurements from the SOLVE/THESEO 2000 Arctic campaign. The method may be used to refine the Nash algorithm, which, due to the inherently coarser resolution of potential vorticity on which it is dependent, may misidentify the inner edge by more than 400 km and omit the identification of small, extravortex filaments within the vortex.

Aerosol optical properties during INDOEX based on measured aerosol particle size and composition

Abstract: The light scattering and light absorption as a function of wavelength and relative humidity due to aerosols measured at the Kaashidhoo Climate Observatory in the Republic of the Maldives during the INDOEX field campaign has been calculated. Using size-segregated measurements of aerosol chemical composition, calculated light scattering and absorption has been evaluated against measurements of light scattering and absorption. Light scattering coefficients are predicted to within a few percent over relative humidities of 20–90%. Single scattering albedos calculated from the measured elemental carbon size distributions and concentrations in conjunction with other aerosol species have a relative error of 4.0% when compared to measured values. The single scattering albedo for the aerosols measured during INDOEX is both predicted and observed to be about 0.86 at an ambient relative humidity of 80%. These results demonstrate that the light scattering, light absorption, and hence climate forcing due to aerosols over the Indian Ocean are consistent with the chemical and physical properties of the aerosol at that location.

Effects of Asian air pollution transport and photochemistry on carbon monoxide variability and ozone production in subtropical coastal south China

Abstract: [1] Surface ozone and carbon monoxide (CO) measured from a relatively remote coastal station in Hong Kong are analyzed to study the effects of pollutant transport and associated ozone production on CO and ozone variations in the subtropical south China region. CO and ozone concentrations show a common minimum in summer and in the maritime air masses from the South China Sea and Pacific Ocean. They have higher values in other seasons and in the continental air masses that have passed over mainland Asia and the East Asian coast. CO shows the maximum monthly median of 457–552 ppbv in winter while ozone shows a maximum of 40–50 ppbv in autumn and a distinct peak of 41–43 ppbv in spring. The CO concentrations especially in the continental air masses (median of 277 to 428 ppbv) are very high when compared with measurements in most parts of the world. This suggests that the south China region is under the strong influence of pollutant transport from the Asian continent and East Asian coast. Ozone and CO show strong positive correlations in the polluted maritime air masses and from late spring to early autumn (May–September) with the linear regression slopes of the ozone-CO plot from 0.08 to 0.22 (with respective standard errors from 0.01 to 0.03). The strong correlations and slopes plus the high CO levels indicate that there is substantial ozone production from pollution in the polluted maritime air masses and in the late spring to early autumn period.

Evidence for the widespread presence of liquid-phase particles during the 1999–2000 Arctic winter

Abstract: [1] In situ Multiangle Spectrometer Probe (MASP) particle measurements have been analyzed to determine the typical behavior of sulfate particles during the SAGE III Ozone Loss and Validation Experiment (SOLVE) campaign. The study has explored variations in the total particle concentration measured by MASP. A new analysis method has been developed in which increases of the MASP concentration can be interpreted as growth of small particles (those which are smaller than 0.2 μm in radius at midlatitudes). The method also allows all of the MASP measurements made during the SOLVE campaign to be incorporated in a single analysis. At all levels of the stratosphere, the total MASP concentration (and therefore aerosol growth) varies continuously with temperature. This behavior is well-reproduced by assuming that the sulfate aerosols are liquid solutions, but cannot be reproduced if the aerosol is assumed to be frozen. At sufficiently cold temperatures, larger increases in the MASP concentration are consistently seen; the observed onset temperature for this growth is in good agreement with model expectations for liquid ternary solutions. Liquid-like behavior is apparent for all measurements made in the Arctic during SOLVE, both inside and outside the vortex, and even at the coldest temperatures sampled during the campaign. At the levels with the coldest measured temperatures, which cause maximum particle sizes and thus the greatest total MASP concentrations, 90% of the particles grow as liquids. Therefore, the freezing that occurred during the 1999–2000 Arctic winter was selective, with most of the particles remaining liquid even in the presence of a small number of frozen particles.

Construction of a unified, high-resolution nitrous oxide data set for ER-2 flights during SOLVE

Abstract: [1] Four nitrous oxide (N2O) instruments were part of the NASA ER-2 aircraft payload during the 2000 SAGE-III Ozone Loss and Validation Experiment (SOLVE). Coincident data from the three in situ instruments and a whole air sampler are compared. Agreement between these instruments was typically good; however, there are several types of important differences between the data sets. These differences prompted a collaborative effort to combine data from the three in situ instruments, using an objective method, to produce a self-consistent, high-resolution, unified N2O data set for each SOLVE flight. The construction method developed by the four N2O instrument teams is described in detail. An important step in this method is the evaluation and reduction of bias in each of the in situ data sets before they are combined. The quality of unified N2O data is examined through its agreement with high-accuracy and high-precision N2O data from whole air samples collected from the ER-2 during SOLVE flights. Typical agreement between these two data sets is 2.9 ppb (1.5%), better than the typical agreement between any pair of N2O instruments.

Mixing events revealed by anomalous tracer relationships in the Arctic vortex during winter 1999/2000

Abstract: [1] During the 1999/2000 Arctic winter SAGE III–Ozone Loss and Validation Experiment (SOLVE) campaign, high-resolution, in situ tracer data measured aboard the NASA ER-2 high-altitude aircraft revealed anomalous mixing events within the polar vortex. From January to March 2000 in the 350–500 K potential temperature range, we found mixing events during 15% of the flight time on average with significant maxima at potential temperatures of 450, 410, and 380 K. The events were spread throughout the vortex but showed a distinct minimum at 73° N and a peak at 85°N equivalent latitude. About 60% of the observed mixing events were less than 13 km wide. Based on a case study of tracer-tracer relationships, an objective simple method is introduced to detect such events using the linear nitrous oxide (N2O):potential temperature relationship observed deep in the vortex. Rigorous analysis and supporting evidence from total water data corroborated the validity of the method. These results suggest mixing across the polar vortex edge occurred preferentially in layers at select altitudes in the Arctic winter 1999/2000.

Cloud liquid water and ice measurements from spectrally resolved near‐infrared observations: A new technique

Abstract: [1] A new technique is presented for the simultaneous measurement of water vapor, liquid water, and water ice in clouds using spectral observations of scattered sunlight between 0.865 and 1.065 μm. A nonlinear least squares approach is used to fit the measurements with the absorption spectral signatures of the vapor, liquid, and solid phases of water. This allows for the retrieval of the total path-integrated column abundances of vapor, liquid, and ice and directly yields the fractional absorption by all three phases of water within clouds at these wavelengths. Laboratory, ground-based, and aircraft-based observations are presented that illustrate the application of this technique and its comparison to other methods of measuring liquid water in widely varying conditions. The results suggest that the retrieval of liquid water is relatively insensitive to interference from other absorbers. The measurement of ice is less accurate and precise than that of liquid and is affected to some degree by the absorption of water vapor and liquid; uncertainty estimates are given. The method provides key information for radiative balance studies and has the potential to aid aviation safety. An extension of this technique to include scattered sunlight at longer wavelengths is likely to produce more accurate results and lower detection limits for both liquid and ice. Applying the technique to shorter wavelengths should allow for retrievals that are less sensitive to photon path distribution uncertainties.

Transport of ozone‐depleted air on the breakup of the stratospheric polar vortex in spring/summer 2000

Abstract: [1] A high-resolution three-dimensional off-line chemical transport simulation has been performed with the SLIMCAT model to examine transport and mixing of ozone depleted air in the lower stratosphere on breakup of the polar vortex in spring/summer 2000 The model included ozone, N2O, and F11 tracers and used simplified chemistry parameterizations The model was forced by T106 European Centre for Medium-Range Weather Forecasts analyses The model results show that, by the end of June, above 420 K, much of the ozone-depleted air is transported from polar regions to the subtropics In contrast, below 420 K, most of the ozone-depleted air remains poleward of approximately 55°N It is suggested that the influence of the upper extension of the tropospheric subtropical jet provides a transport barrier at lower levels, while strong stirring on breakup of the polar vortex is important at upper levels The mean meridional circulation modifies the distribution of ozone-depleted air by moving it up the subtropics and down in the extratropics The model simulation is validated by comparing vertical profiles of ozone loss against ozonesonde measurements The model results are consistent with many of the features present in the ozonesonde measurements F11-N2O correlation plots are examined in the model and they show distinct canonical correlation curves for the polar vortex, midlatitudes, and the tropics Comparison against balloon and aircraft measurements show that the model reproduces the separation between the vortex and midlatitude curves; however, the ratio of N2O to F11 lifetimes is somewhat too small in the model It is shown that anomalies from the midlatitude canonical correlation curve can be used to identify remnants of polar vortex air which has mixed with midlatitude air At the end of June there is excellent agreement in the position of air with anomalous F11-N2O tracer correlation and ozone-depleted air from the polar vortex

Broadband shortwave calibration results from the Atmospheric Radiation Measurement Enhanced Shortwave Experiment II

Abstract: [1] The second ARM (Atmospheric Radiation Measurement) Enhanced Shortwave Experiment (ARESE II) used a single aircraft flying above the north central Oklahoma Southern Great Plains ARM central facility to measure the atmospheric absorption in the column of air between the surface and the Twin Otter altitude ceiling around 7 km on both clear and overcast days. For this experiment, three types of broadband radiometers were used to measure upwelling and downwelling shortwave flux on the aircraft at 7 km. This provided redundancy that was lacking in the first ARESE. Further, all instruments used on the ground and on the aircraft were calibrated on the ground against the same radiation standard. Preflight and postflight comparisons of the broadband instruments used on the aircraft during the flight series with the standard, and comparisons of the ground instruments with the standard during the flights, suggest agreement much better than the target uncertainty of 20 W/m2 at the 95% confidence level. Comparisons of the standard and the aircraft instruments for low-altitude passes on clear days indicate more uncertainty as expected for a nonstationary platform. The estimated uncertainty in the measured column absorption based on the difference in measured net irradiances at the surface and near 7 km at the 95% confidence level is 20 W/m2.