bluuebunny/crossref_metadata_2025 huggingface dataset:
Impact of vegetation properties on U.S. summer weather prediction
Authors: Xue Yongkang , Fennessy Michael J. , Sellers Piers J.
Published: February 2004

Systematic biases in U.S. summer integrations with the Center for Ocean‐Land‐Atmosphere Studies (COLA) atmospheric general circulation model (GCM) have been identified and analyzed. Positive surface air temperature biases of 2°–4°K occurred over the central United States. The temperature biases were coincident with the agricultural region of the central United States, where negative precipitation biases also occurred. The biases developed in June and became very significant during July and August. The impact of the crop area vegetation and soil properties on the biases was investigated in a series of numerical experiments. The biases were largely caused by the erroneous prescription of crop vegetation phenology in the surface model of the GCM. The prescribed crop soil properties also contributed to the biases. On the basis of these results the crop model has been improved and the systematic errors in the U.S. summer simulations have been reduced. The numerical experiments also revealed that land surface effects on the atmospheric variables at and near the surface during the North American summer are very pronounced and persistent but are largely limited to the area of the anomalous land surface forcing. In this regard, the midlatitude land surface effects described here are similar to those previously found for tropical regions.
Comparison of hydroperoxide measurements made during the Mauna Loa Observatory Photochemistry Experiment 2
Authors: Staffelbach Thomas A. , Kok Gregory L. , Heikes Brian G. , McCully Brian , Mackay Gervase I. , Karecki David R. , Schiff Harold I.
Published: February 2004

From the fall of 1991 through the summer of 1992 the Mauna Loa Observatory Photochemistry Experiment 2 (MLOPEX 2) took place in Hawaii. The experiment consisted of four intensive research periods, each approximately 1 month in duration. We report a comparison of measurements of atmospheric hydroperoxide and methylhydroperoxide as measured during MLOPEX 2a (September 16 to October 23, 1991) and MLOPEX 2b (January 15 to February 15, 1992). The analytical techniques used for measuring hydroperoxides included tunable diode laser infrared absorption (TDLAS) and fluorescence from an enzymatically produced dimer. The TDLAS technique measured hydrogen peroxide (H2O2) only. Three different procedures were utilized to distinguish between H2O2 and organic hydroperoxides in the fluorescence analytical techniques. These were high performance liquid chromatographic (HPLC) separation, enzymatic discrimination, and differential aqueous solubility. The measured concentrations ranged from 0 to 2 parts per billion by volume (ppbv) for H2O2 and 0 to ppbv for methylhydroperoxide (CH3OOH). Depending on the time period of measurement, the agreement varied between 20% and a factor of 2 or more for the measurement of H2O2. The discrepancy for the CH3OOH data was larger.
Issues in aerosol measurement for optics assessments
Authors: McMurry Peter H. , Zhang Xinqiu , Lee Chung‐Te
Published: February 2004

Size‐resolved composition, water content, and mixing characteristics of fine (<2μm) particles were measured during intensive field studies in Los Angeles (Southern California Air Quality Study (SCAQS)(1987)) and at the Grand Canyon (winter 1990, summer 1992). Aerosol optical properties were calculated from these measurements using Mie theory. Calculated scattering coefficients are in reasonable agreement with directly measured values for internal and external mixing models as well as for a hybrid model based on measured mixing characteristics. Calculated dry sulfate mass scattering efficiencies cover the range reported in previous studies based on multiple linear regression analysis (MLR) (∼3 to 7 m2/g) but increase systematically with size and are sensitive to assumptions regarding the chemical mechanism of secondary aerosol formation. Calculated organic carbon (1.4*mass of carbon associated with particulate organics) scattering efficiencies (∼3 to 7 m2/g ) show no systematic dependence on median size but are somewhat higher than previously published estimates based largely on MLR. Organic carbon and sulfates were the dominant contributors to fine particle scattering in both Grand Canyon studies (50 and 38% during the 1990 Navajo Generating Station (NGS) study, respectively, and 48 and 40% at Meadview). However, large discrepancies are found for organic carbon concentrations measured with different samplers, especially in the desert Southwest where concentrations are low. These observations underline the need for improved sampling and characterizing methodologies for carbon‐containing particulate species.
Vertical profiles of N2O5 along with CH4, N2O, and H2O in the late Arctic winter retrieved from MIPAS‐B infrared limb emission measurements
Authors: Wetzel G. , von Clarmann T. , Oelhaf H. , Fischer H.
Published: February 2004

Vertical profiles of N2O5, CH4, N2O, and H2O inside the arctic vortex were retrieved from nighttime infrared limb emission spectra obtained during a flight of the Michelson interferometer for passive atmospheric sounding, balloonborne version (MIPAS‐B) Fourier spectrometer from Kiruna (Sweden, 68°N) on March 14/15, 1992, as part of the European Arctic Stratospheric Ozone Experiment. Spectra were analyzed by a nonlinear multiparameter least squares fitting procedure in combination with an onion‐peeling retrieval algorithm. The N2O5 results were derived from the intensity of the v12 band near 8 μm. These data represent the first ever reported N2O5 profile inside the polar vortex. Between 21.5 and 31.7 km altitude, N2O5 mixing ratios from 0.38 to 0.74 parts per billion by volume (ppbv) were inferred. Below 21.5 km there is a steep decrease in the mixing ratio toward values lower than 0.07 ppbv at 18.9 and 16.1 km. This discontinuity in the vertical profile correlates in altitude with the bulk of the Pinatubo aerosol layer inside the arctic vortex. N2O5 concentrations are calculated as a function of time since local sunset by using initial NO2 concentrations, O3 concentrations, aerosol surface area densities, and reaction rate coefficients, as found in the literature; calculated N2O5 concentrations are consistent with the MIPAS results. These suggest efficient heterogeneous hydrolysis of N2O5 having taken place on sulphate aerosol particles. Retrieved CH4 and N2O profiles reflect the subsided polar vortex air.
Ozone over southern Africa during SAFARI‐92/TRACE A
Authors: Thompson A. M. , Diab R. D. , Bodeker G. E. , Zunckel M. , Coetzee G. J. R. , Archer C. B. , McNamara D. P. , Pickering K. E. , Combrink J. , Fishman J. , Nganga D.
Published: February 2004

Characteristics of total O3 in southern Africa and over the adjacent Atlantic during the IGAC/STARE/SAFARI‐92/TRACE A (International Global Atmospheric Chemistry/South Tropical Atlantic Regional Experiment/Southern African Fire Atmospheric Research Initiative/Transport and Atmospheric Chemistry near the Equator‐Atlantic) field experiments are described. Most of the analysis is based on data from the Nimbus 7/total ozone mapping spectrometer (TOMS) gridded O3 data archive (version 6.0), which is used to examine O3 in terms of seasonal and interannual variability. Total O3 column variability is compared to the tropospheric O3 column derived from balloonborne ozonesondes at four fixed SAFARI‐92/TRACE A sites (Ascension Island, Brazzaville, Okaukuejo, and Irene) from September 1 to October 23, 1992. All of these sites except Okaukuejo had regular ozonesonde launches from 1990 to 1992. Total O3 and integrated tropospheric O3 at the sounding sites showed the expected September–October maxima over southern Africa and the adjacent Atlantic Ocean. Statistical analysis of the TOMS record for 1979–1992 allows disaggregation of components contributing to total O3 variability: Signals due to semiannual and annual cycles and the quasi‐biennial oscillation are identified at the sounding sites. The tropospheric O3 column estimated from integrated sondes (to ∼16 km) at the four sites ranged from 24 to 62 Dobson units (DU) (mean, 45 DU) and averaged 15% of total O3 at Irene (14 launches) and 19% of total O3 at Ascension (20 launches). Tropospheric O3 was higher at Ascension and Brazzaville than at the sites south of 15°S because transport from biomass burning regions was more direct at these sites. This transport is seen in Hovmöller (time‐longitude) plots of total O3. A comparison of 1990–1992 integrated tropospheric O3 amounts with the annual total ozone cycle shows that tropospheric ozone variations may account for all of the annual signal at Ascension (8°S) and Brazzaville (4°S) but only 30–40% of the seasonal total O3 variation at Irene (26°S). Hovmöller plots of daily TOMS O3 over southern Africa and the Atlantic show easterly flow of local O3 maxima at 0°–10°S and westerly movement from 30°–40°S. At 0°–10°S the continent‐ocean total O3 gradient and Ascension and Brazzaville O3 soundings are used to estimate a photochemical O3 formation rate of 1–2 ppbv O3/d over the Atlantic. This agrees with model calculations of moderately aged biomass burning emissions from SAFARI‐92/TRACE A [Jacob et al., this issue; Thompson et al., 1996, this issue].
Gas phase atmospheric bromine photochemistry
Authors: Lary D. J.
Published: February 2004

This paper reviews the current knowledge of gas phase bromine photochemistry and presents a budget study of atmospheric bromine species. The effectiveness of the ozone catalytic loss cycles involving bromine is quantified by considering their chain length and effectiveness. The chain effectiveness is a new variable defined as the chain length multiplied by the rate of the cycle's rate‐limiting step. The chain effectiveness enables a fair comparison of different catalytic cycles involving species which have very different concentrations. This analysis clearly shows that below 25 km the BrO/ClO and BrO/HO2 cycles are among the most important ozone destruction cycles.
Airborne nitrous oxide observations over the western Pacific Ocean: September–October 1991
Authors: Collins James E. , Sachse Glen W. , Anderson Bruce E. , Harriss Robert C. , Bartlett Karen B. , Sandholm Scott , Wade Larry O. , Burney Lewis G. , Hill Gerald F.
Published: February 2004

The Langley tunable diode laser instrument package incorporated an additional channel to measure nitrous oxide (N2O) during the Pacific Exploratory Mission (PEM) West A. These measurements represent the first airborne, fast response (5‐s) N2O data set obtained within the troposphere. Most data were recorded over the western Pacific between 0°N and 45°N latitude, 110°E and 180°E longitude, and 0.3 to 12 km altitude. Important observations include a decreasing N2O latitude gradient of approximately 0.4 parts per billion volume (ppbv) from northern midlatitudes to the equator, a decreasing N2O longitude gradient of 0.4 ppbv from the western Pacific to the central Pacific at northern midlatitudes, and an enhancement of 0.2 ppbv in the boundary layer (altitudes below 0.5 km) relative to the rest of the tropospheric vertical profile. Other observations include increased N2O mixing ratios within both urban and biogenic affected air masses and reduced N2O mixing ratios in stratospheric intrusions. These relationships with air mass source characteristics are exhibited in the large‐scale correlations between N2O and CO, CH4, and CO2 in the free troposphere. Atmospheric inputs of N2O are examined and the relative strengths of continental biogenic and anthropogenic/industrial sources are estimated. The data set is also examined for evidence of an oceanic source of N2O.
Intercomparing the Twomey method with a multimodal lognormal approach to retrieve the aerosol size distribution
Authors: Amato U. , Di Bello D. , Esposito F. , Serio C. , Pavese G. , Romano F.
Published: February 2004

This paper concentrates on intercomparing an objective algorithm to estimate the columnar aerosol size distribution from aerosol spectral extinction and a widespread robust nonparametric inversion approach. The nonparametric approach which has been considered is the Phillips‐Twomey second‐derivative regularization method. The parametric approach assumes that the size distribution is the linear combination of a set of lognormal functions (typically, from 10 to 30 distributions are considered) which have suitable mode radii and standard deviations. Intercomparisons have been performed on the basis of aerosol optical thicknesses derived by high‐resolution solar radiation absorption spectra in the spectral region 0.40 − 1.1 μm. Absorption spectra were recorded by a grating spectrometer with a resolution of 0.5 nm. Each inversion, either parametric or nonparametric, was obtained by using more than 450 data points at a time which, from a statistical point of view, allowed us to obtain high‐quality results. For the cases presented here, we found that the two approaches agree fairly well in indicating the most significant characteristics of the aerosol size distribution.
Airborne studies of emissions from savanna fires in southern Africa: 1. Aerosol emissions measured with a laser optical particle counter
Authors: Le Canut P. , Andreae M. O. , Harris G. W. , Wienhold F. G. , Zenker T.
Published: February 2004

During the SAFARI‐92 experiment (Southern Africa Fire Atmosphere Research Initiative, September–October 1992), we flew an instrumented DC‐3 aircraft through plumes from fires in various southern African savanna ecosystems. Some fires had been managed purposely for scientific study (e.g., those in Kruger National Park, South Africa), while the others were “fires of opportunity” which are abundant during the burning season in southern Africa. We obtained the aerosol (0.1–3.0 μm diameter) number and mass emission ratios relative to carbon monoxide and carbon dioxide from 21 individual fires. The average particle number emission ratio ΔN/ΔCO (Δ: concentrations in plume minus background concentrations) varied between 14 ± 2 cm−3ppb−1for grasslands and 23 ± 7 cm−3ppb−1for savannas. An exceptionally high value of 43 ± 4 cm−3ppb−1was measured for a sugarcane fire. Similarly, the mass emission ratio ΔM/ΔCO varied from 36 ± 6 ng m−3ppb−1to 83 ± 45 ng m−3ppb−1, respectively, with again an exceptionally high value of 124 ± 14 ng m−3ppb−1for the sugarcane fire. The number and mass emission ratios relative to CO depended strongly upon the fire intensity. Whereas the emission ratios varied greatly from one fire to the other, the aerosol number and volume distributions as a function of particle size were very consistent. The average background aerosol size distribution was characterized by three mass modes (0.2–0.4 μm, ≈1.0 μm, and ≈2.0 μm diameter). On the other hand, the aerosol size distribution in the smoke plumes showed only two mass modes, one centered in the interval 0.2–0.3 μm and the other above 2 μm diameter. From our mean emission factor (4 ± 1 g kg−1dm) we estimate that savanna fires release some 11–18 Tg aerosol particles in the size range 0.1–3.0 μm annually, a somewhat lower amount than emitted from tropical forest fires. Worldwide, savanna fires emit some 3–8 × 1027particles (in the same size range) annually, which is expected to make a substantial contribution to the cloud condensation nuclei population in the tropics.
First‐order sensitivity and uncertainty analysis for a regional‐scale gas‐phase chemical mechanism
Authors: Gao Dongfen , Stockwell William R. , Milford Jana B.
Published: February 2004

First‐order sensitivity and uncertainty analysis methods have been applied to the RADM2 mechanism, the second generation gas‐phase chemical mechanism included in the Regional Acid Deposition Model. The direct decoupled method (DDM) was used to evaluate the local sensitivity of product concentrations of O3, HCHO, H2O2, PAN, and HNO3 to values of 157 rate constants and 126 stoichiometric coefficients. The sensitivity analysis results were combined with estimates of the uncertainty in each parameter in the mechanism to produce a local measure of its contribution to the uncertainty in the outputs. Several different sets of simulation conditions were used, representing summertime surface conditions for urban and nonurban areas. The analysis identified the most influential rate parameters to be those for PAN chemistry, formation of HNO3, and photolysis of HCHO, NO2, O3, and the unknown product (DCB) of aromatics oxidation. Rate parameters for the conversion of NO to NO2, such as O3 + NO, HO2 + NO and organic radical + NO, and the product yields of organic peroxy radical (XYLP) in the reaction of XYL + HO (XYL represents xylene and more reactive aromatics) and DCB in the reaction XYLP + NO are also relatively influential.
Nocturnal observations of the semidiurnal tide at a midlatitude site
Authors: Niciejewski R. J. , Killeen T. L.
Published: February 2004

Fabry‐Pérot interferometer observations of the mesospheric hydroxyl emission and the lower thermospheric O I (5577Å) emission have been conducted from an airglow observatory at a dark field site in southeastern Michigan for the past several years. The primary functions of the observatory are to provide a database for correlative observations with the UARS satellite and to provide a synoptic measurement program for the coupling energetics and dynamics of atmospheric regions effort. An intensive operational effort between May 1993 and July 1994 has resulted in a substantial data set from which neutral winds have been determined from the bifilter acquisition sequence. A “best fit” analysis in the least squares sense of the simultaneous measurements of the neutral winds to a 12‐hour periodicity has provided amplitude and phase parameters for the semidiurnal tide as well as a measure of the mean wind. The measured tidal amplitude is greater at the higher altitude, though the seasonal behavior at both altitudes is similar with greater amplitudes during August/September and April/May. Both meridional and zonal wind components are consistent with a semidiurnal tidal description during the entire observational sequence except for the May to July 1993 period. The mean winds show annual variation in the meridional flow, being equatorward from May to October and poleward during the winter. The zonal flow is primarily eastward during the entire observational window with higher speed flows during May/June at the higher altitude and June/July at the lower altitude. A comparison with a semidiurnal tidal model indicates that the measured tidal amplitudes are a factor of 2 times greater, while the phases show similar equinoctial transitions.
Scales of temporal and spatial variability of midlatitude soil moisture
Authors: Vinnikov Konstantin Y. , Robock Alan , Speranskaya Nina A. , Schlosser C. Adam
Published: February 2004

Soil moisture observations from direct gravimetric measurements in Russia are used to study the relationship between soil moisture, runoff, and water table depth for catchments with different vegetation types, and to estimate the spatial and temporal correlation functions of soil moisture for different soil layers. For three catchments at Valdai, Russia, one with a grassland, one with an old forest, and one with a growing forest, the interannual soil moisture variations are virtually the same for the 31‐year period, 1960–1990. The runoff is higher for the grassland than for the old forest, and the water table depth is not as deep. The runoff and water table for the growing forest vary from grassland‐like during the first decade, when the trees are small, to old forest‐like at the end of the period. The seasonal cycle of soil moisture is similar at all three catchments, but the snowmelt and summer drying begin a month earlier at the grassland than in the forests. A statistical model of both temporal and spatial variations in soil moisture is developed that partitions the variations into red noise and white noise components. For flat homogeneous plots, the white noise component is relatively small and represents solely random errors of measurement. For natural landscapes with variable vegetation and soil types, and complicated topography, this component is responsible for most of the temporal or spatial variance. The red noise component of temporal variability is in good agreement with theory. The timescale of this component is equal to the ratio of field capacity of soil to potential evapotranspiration, approximately 3 months. The red noise component of spatial variability reflects the statistical properties of the monthly averaged precipitation field. The scale of spatial correlation of this component is about 500 km. The estimates of scales of temporal and spatial correlation do not differ significantly for water content in the top 20‐cm and 1‐m layers of soil. These results have important implications for both remote sensing of soil moisture and soil moisture parameterization in climate models.
Diurnal variability of mesospheric ozone as measured by the UARS microwave limb sounder instrument: Theoretical and ground‐based validations
Authors: Ricaud P. , de La Noë J. , Connor B. J. , Froidevaux L. , Waters J. W. , Harwood R. S. , MacKenzie I. A. , Peckham G. E.
Published: February 2004

Diurnal variability of mesospheric ozone as measured by the 183‐GHz radiometer of the UARS microwave limb sounder (MLS) instrument for the northern midlatitudes in October 1991 and 1992 is compared with theoretical calculations of diurnal amplitudes produced by two photochemical models and with ground‐based microwave measurements made from Bordeaux (France, 45°N) in October 1988, 1989, and 1990 and the Table Mountain Facility (California, 35°N) in October 1990. Great care has been taken in comparing all the data sets within the same frame, i.e., interpolating onto the same vertical grid (pressure or altitude), using the same units (concentration or mixing ratio) and degrading the vertical resolution of some data or models (convolution of the vertical profiles with appropriate averaging kernels). MLS diurnal variability generally agrees to within 10% with ground‐based and model results at 0.5, 0.2, 0.1, and 0.05 hPa (approximately 55, 60, 65, and 70 km, respectively). Although modeled diurnal changes at 55 ± 8 km are closer to the ground‐based Bordeaux measurements than to the MLS data at 45°N, MLS results are closer to ground‐based Table Mountain Facility data at 35°N at 0.42 and 0.22 hPa (∼55 ± 8 and ∼60 ± 8 km, respectively) than to models. At 0.1 and 0.042 hPa, MLS diurnal changes are weaker than ground‐based and model variations, but daytime O3 mixing ratios are found to be in very good agreement for all data sets.
Comparison of free tropospheric western Pacific air mass classification schemes for the PEM‐West A experiment
Authors: Smyth S. , Bradshaw J. , Sandholm S. , Liu S. , McKeen S. , Gregory G. , Anderson B. , Talbot R. , Blake D. , Rowland S. , Browell E. , Fenn M. , Merrill J. , Bachmeier S. , Sachse G. , Collins J. , Thornton D. , Davis D. , Singh H.
Published: February 2004

During September/October 1991, NASA's Global Tropospheric Experiment (GTE) conducted an airborne field measurement program (PEM‐West A) in the troposphere over the western Pacific Ocean. In this paper we describe and use the relative abundance of the combustion products C2H2 and CO to classify air masses encountered during PEM‐West A based on the degree that these tracers were processed by the combined effects of photochemical reactions and dynamical mixing (termed the degree of atmospheric processing). A large number of trace compounds (e.g., C2H6, C3H8, C6H6, NOy, and O3) are found to be well correlated with the degree of atmospheric processing that is reflected by changes in the ratio of C2H2/CO over the range of values from ∼0.3 to 2.0 (parts per trillion volume) C2H2/(parts per billion volume) CO. This C2H2/CO‐based classification scheme is compared to model simulations and to two independent classification schemes based on air mass back‐trajectory analyses and lidar profiles of O3 and aerosols. In general, these schemes agree well, and in combination they suggest that the functional dependence that other observed species exhibit with respect to the C2H2/CO atmospheric processing scale can be used to study the origin, sources, and sinks of trace species and to derive several important findings. First, the degree of atmospheric processing is found to be dominated by dilution associated with atmospheric mixing, which is found to primarily occur through the vertical mixing of relatively recent emissions of surface layer trace species. Photochemical reactions play their major role by influencing the background concentrations of trace species that are entrained during the mixing (i.e., dilution) process. Second, a significant noncontinental source(s) of NO (and NOx) in the free troposphere is evident. In particular, the enhanced NO mixing ratios that were observed in convected air masses are attributed to either emissions from lightning or the rapid recycling of NOy compounds. Third, nonsoluble trace species emitted in the continental boundary layer, such as CO and hydrocarbons, are vertically transported to the upper troposphere as efficiently as they are to the midtroposphere. In addition, the mixing ratios of CO and hydrocarbons in the upper troposphere over the western Pacific may reflect a significant contribution from northern hemisphere land areas other than Asia. Finally, we believe that these results can be valuable for the quantitative evaluation of the vertical transport processes that are usually parameterized in models.
Seasonal variations of methanesulfonate, non‐sea‐salt sulfate, and sulfur dioxide at three sites in Canada
Authors: Li Shao‐Meng , Barrie L. A. , Toom D.
Published: February 2004

Daily air measurements at one midcontinental and two coastal sites on the Atlantic Ocean and Pacific Ocean in Canada during April 1992 to June 1993 are used to show the seasonality of methanesulfonate (MSA), non‐sea‐salt (nss) SO4=, and SO2. At the Atlantic site, Kejimkujik National Park, Nova Scotia (44°22′N, 65°12′W), the concentration ranges were <0.002–0.13, 0.2–26, and <0.2–10 μg m−3 for MSA, nss SO4=, and SO2, respectively, and the annual means were 0.02, 2.2, and 1.3 μg m−3. MSA had a monthly median peak of 0.036 μg m−3 in June, versus an SO2 peak of 2.7 μg m−3 in February, and no discernible nss SO4= seasonal peak. The MSA/nss SO4= ratios were low compared to ratios in other parts of the world but exhibited a seasonality dominated by that in MSA. At the midcontinental site, Experimental Lake Area, Ontario (49°39′N, 93°43′W), the concentrations were usually lower than at the coastal sites. The ranges were <0.002–0.066, 0.04–12.5, and <0.16–16.6 μg m−3 for MSA, nss SO4=, and SO2, respectively, and the annual means were 0.01, 1.6, and 0.93 μg m−3. The monthly median seasonal peaks at this site were 0.01 μg m−3 for MSA in September, 2.1 μg m−3 for nss SO4= in March, and 2.8 μg m−3 for SO2 in January. The MSA/nss SO4= ratio at this site was similar to that found at Kejimkujik. At Saturna Island, British Columbia (48°47′N, 123°08′W), the ranges were 0.002–0.2, 0.14–6.4, and 0.12–21 μg m−3 for MSA, nss SO4=, and SO2, respectively, and the annual means were 0.06, 1.1, and 3.0 μg m−3. The monthly median peaks were 0.12 μg m−3 for MSA in August, 5 μg m−3 for SO2 in February, and a nominal peak of 1.5 μg m−3 for nss SO4= in August. The MSA/nss SO4= ratio had a seasonal pattern dominated by that of MSA with a peak of 0.1 in August. These data should enhance the existing databases for testing global sulfur models.
Tropospheric ozone during Mauna Loa Observatory Photochemistry Experiment 2 compared to long‐term measurements from surface and ozonesonde observations
Authors: Oltmans Samuel J. , Hofmann David J. , Lathrop Jeffrey A. , Harris Joyce M. , Komhyr Walter D. , Kuniyuki Darryl
Published: February 2004

Continuous surface ozone measurements have been made at Mauna Loa Observatory (MLO) for 20 years. In addition, weekly ozone profile measurements using balloonborne ozonesondes have been carried out from Hilo, Hawaii, since 1985. These long‐term records are compared with data obtained during the MLOPEX 2 period from September 1991 to August 1992. Ozone behavior at the observatory level (∼3.4 km) during autumn and winter of 1991–1992 was similar to that found during the period 1980–1990. In spring and summer 1992, however, there were several significant differences from the long‐term behavior. During March and April 1992, there was about 10% more ozone than the long‐term average, and the variability was less than half of what is seen normally. These characteristics are associated with strong flow from the north and west. Both June and July 1992 saw periods of elevated ozone with the June average 20% higher than normal. During the more limited sampling (weekly profiles) when ozonesonde measurements were made, the 1992 spring enhancement was particularly pronounced at 500 mbar (∼6 km), while during the summer the larger than normal concentrations were at 700 mbar (∼3.5 km). In the upper troposphere, on the other hand, spring ozone amounts in 1992 were much below normal with only about half the ozone usually seen in the 12‐ to 15‐km region. The ozone profiles are discussed in terms of the representativeness of the MLO surface measurements in characterizing the free troposphere ozone behavior at both the altitude of the observatory as well as other heights in the atmosphere. During the winter and spring, the MLO measurements are often representative of behavior over a broad depth of the troposphere (3–10 km). In the summer and autumn the MLO observations are more characteristic of free tropospheric conditions at or near the observatory level.
Iterative bulk exchange model for estimating air‐water transfer of HNO3
Authors: Valigura R. A.
Published: February 2004

Air‐water exchange rates have been estimated for most nitrogen species over open ocean; however, these rates may not apply to coastal areas due to different meteorological conditions. In coastal areas the primary obstacle to estimating the exchange rate has been the lack of near‐surface, over‐water meteorological data for mesoscale model input. To address this need, a network of buoys has been deployed in Chesapeake Bay. The two objectives of this project were (1) to develop and evaluate an iterative bulk exchange model to estimate air‐water exchange of heat, water, and momentum from buoy data and (2) to use the model outputs to estimate air‐water transfer rates of nitric acid (HNO3). In a previous study a similar approach to that used in this study was applied to sulfur dioxide (SO2). The analyses performed in this study demonstrate the need to determine if variability in HNO3 concentration is significantly correlated with the corresponding variability in transfer rate to Chesapeake Bay. The theoretical limitations associated with this approach were lack of homogeneous conditions in the coastal zone and the inadequacy of similarity theory to describe turbulent conditions measured. The approach used in this study should be applicable to other hygroscopic chemicals in addition to HNO3 and SO2 (e.g., ammonia).
Differences in the reactivity of type I polar stratospheric clouds depending on their phase
Authors: Ravishankara A. R. , Hanson D. R.
Published: February 2004

It has been suggested that some Type I polar stratospheric clouds (PSCs) are supercooled liquids containing sulfuric acid, water, and nitric acid. We show that the activation of chlorine over supercooled liquids is comparable to that over solid Type I PSCs at the same temperature. Furthermore, at temperatures within a few degrees of the frost point, the reactions of ClONO2 with HCl and H2O, that of HOCl with HCl, and the hydrolysis of N2O5 would be faster if Type I PSCs are liquid solutions rather than solids. Thus chlorine can be rapidly activated without the formation of solid Type I PSCs.
Photochemical evolution of ozone in the lower tropical stratosphere
Authors: Avallone L. M. , Prather M. J.
Published: February 2004

Rarely does the atmosphere allow direct observation of the photochemical evolution of ozone. In most of the troposphere and lower stratosphere this slow chemistry cannot be understood without including much larger changes caused by the circulation. Yet in the tropical stratosphere, where ozone‐poor air of tropospheric origin enters and rises slowly in near isolation, it can be demonstrated that O3 is created by dissociation of O2 at a rate consistent with current theory. The parallel photolytic destruction of the unreactive source gases (for example, N2O and CFCl3) and the consequent evolution of chemically active odd‐nitrogen (NOy) and chlorine (Cly) species, however, indicate a small amount of mixing of much older, photochemically aged air from the midlatitude stratosphere into this tropical plume.
Reaction kinetics of ozone at low concentrations with n‐hexane soot
Authors: Smith D. M. , Chughtai A. R.
Published: February 2004

The reaction of ozone in low concentrations (2.6–41.2 ppm) with n‐hexane soot has been studied by interfacing Fourier transform‐infrared spectroscopy with a long optical path cell and microgravimetry. The rates and rate laws for ozone loss, soot mass gain, and CO2 and H2O formation have been determined at 22°C. The rates and the rate laws associated with the increase of soot mass, due primarily to the formation of surface carboxylics, show differences between freshly‐prepared and aged soot. Part of this difference has its origin in the adsorption of molecular oxygen, which participates in the ozone‐soot reaction. Material balance calculations reveal that while O3 decomposition exceeds O‐containing product formation (CO2, H2O, carboxylics), one stage of the reaction shows excess product apparently due to the involvement of O2. A complex reaction sequence is seen to involve essentially three reaction stages: a rapid initial catalytic O3 decomposition, followed by rapid mass increase and CO2 and H2O evolution, continuing with a long period of oxidation during which the rate of ozone loss is second order in ozone. The latter observation implies the involvement of atomic oxygen in the oxidation process.
Temporal changes of Mount Pinatubo aerosol characteristics over northern midlatitudes derived from SAGE II extinction measurements
Authors: Anderson John , Saxena V. K.
Published: February 2004

The June 12–16, 1991, eruption of Mount Pinatubo in the Philippines injected an estimated 20 Mt of sulfur dioxide gas well into the stratosphere and is the largest volcanic event recorded in recent history. The Stratospheric Aerosol and Gas Experiment (SAGE) II satellite has provided unprecedented information on the evolution of the Pinatubo aerosol since its eruption. The Pinatubo aerosol size distributions are inferred from SAGE II extinction measurements using a randomized minimization search technique in the radii range of 0.1–0.8 μm in 0.1‐μm increments. The Pinatubo aerosol characteristics between 13 and 30 km and columnar characteristics in a unit column between 15 and 25 km are then derived. The latitudinal span is between 30° and 60°N from March 1991 to March 1994. During this period, the maximum surface area was observed to exceed 50 μm2 cm−3. The vertically averaged surface areas were of the order of 27.74 ± 12 μm2 cm−3 in March 1993 at a height of 14.5 km. The corresponding averaged mass loading was of the order of 4.23 ± 1.37 μg m−3. During March 1994, the peak surface areas and mass loading at 14.5 km were of the order of 9.85 ± 3.87 μm2 cm−3 and 1.02 ± 0.28 μg m−3, respectively, still larger with respect to the volcanically unperturbed values of 0.98 ± 0.54 μm2 cm−3 and 0.12 ± 0.04 μg m−3 observed during March 1991. Columnar mass loading, surface area, and number concentrations have approached preemption background levels, whereas the columnar mean effective radius is still 2–3 times greater as of March 1994.
Chemical and physical properties of plumes of anthropogenic pollutants transported over the North Atlantic during the North Atlantic Regional Experiment
Authors: Daum P. H. , Kleinman L. I. , Newman L. , Luke W. T. , Weinstein‐Lloyd J. , Berkowitz C. M. , Busness K. M.
Published: February 2004

Plumes of photochemical pollutants transported from the industrialized regions of the northeast United States and Canada were sampled over the North Atlantic Ocean at distances up to 1000 km from the coast. The plumes were found in well defined layers up to 1 km thick and were usually isolated from the surface by a low altitude inversion. Plume composition was consistent with the occurrence of extensive photochemical processing during transit from source regions as indicated by high O3 concentrations (O3 maximum ∼150 parts per billion by volume (ppbv)), generally high fractional conversion (>85%) of NOx to its oxidation products, and high peroxide concentrations (median 3.6 ppbv; maximum 11 ppbv). These observations are in accord with processing times estimated from back trajectory analysis. CO and O3 concentrations were well correlated (r2 = 0.64) with a slope (0.26) similar to previous measurements in photochemically aged air. Good correlations were also observed between CO and accumulation mode particle number densities (r2 = 0.64), and CO and NOy (r2 = 0.67). O3 was found to depend nonlinearly on the NOx oxidation product concentration. At low values of (NOy‐NOx), the slope (14) was within the range of values measured previously in photochemically aged air masses, at higher concentrations the slope was much lower (4.6). The low slope at high concentrations is attributed to minimization of losses of NOx oxidation products in spatially well‐defined plumes during transport. A strong linear correlation (r2 = 0.73) was found between O3, and the concentration of radical sink species as represented by the quantity ((NOy‐NOx) + 2H2O2).
A reevaluation of the open ocean source of methane to the atmosphere
Authors: Bates Timothy S. , Kelly Kimberly C. , Johnson James E. , Gammon Richard H.
Published: February 2004

Seawater and atmospheric methane (CH4) mixing ratios were measured on five cruises throughout the Pacific Ocean from 1987 to 1994 to assess the magnitude of the ocean‐atmosphere flux. The results showed consistent regional and seasonal variations with surface seawater concentrations ranging from 1.6 to 3.6 nM and saturation ratios ranging from 0.95 to 1.17. The equatorial Pacific Ocean was supersaturated with respect to atmospheric CH4 partial pressures, while areas outside the tropics often were undersaturated during fall and winter. Although atmospheric CH4 mixing ratios over the North Pacific during April increased 3.4% from 1988 to 1993, the saturation ratios remained constant. Based on the concentration fields, the data were divided into two seasons and 10 latitude zones from 75°S to 75°N. Using monthly Comprehensive Ocean‐Atmosphere Data Set (COADS) wind and surface seawater temperature data and the Wanninkhof [1992] wind speed/transfer velocity relationship, the calculated zonal average fluxes ranged from −0.1 to 0.4 μmol m−2 d−1. The combined seasonal and zonal fluxes result in a total global ocean‐to‐atmosphere flux of 25 Gmol yr−1 (0.4 Tg CH4 yr−1), which is an order of magnitude less than previous estimates [Intergovernmental Panel on Climate Change (IPCC), 1994]. The estimated uncertainty in this number is approximately a factor of 2.
Validation of O(1S) wind measurements by WINDII: the WIND Imaging Interferometer on UARS
Authors: Gault W. A. , Thuillier G. , Shepherd G. G. , Zhang S. P. , Wiens R. H. , Ward W. E. , Tai C. , Solheim B. H. , Rochon Y. J. , McLandress C. , Lathuillere C. , Fauliot V. , Hersé M. , Hersom C. H. , Gattinger R. , Bourg L. , Burrage M. D. , Franke S. J. , Hernandez G. , Manson A. , Niciejewski R. , Vincent R. A.
Published: February 2004

This paper describes the current state of the validation of wind measurements by the wind imaging interferometer (WINDII) in the O(1S) emission. Most data refer to the 90‐to‐110‐km region. Measurements from orbit are compared with winds derived from ground‐based observations using optical interferometers, MF radars and the European Incoherent‐Scatter radar (EISCAT) during overpasses of the WINDII fields of view. Although the data from individual passes do not always agree well, the averages indicate good agreement for the zero reference between the winds measured on the ground and those obtained from orbit. A comparison with winds measured by the high resolution Doppler imager (HRDI) instrument on UARS has also been made, with excellent results. With one exception the WINDII zero wind reference agrees with all external measurement methods to within 10 m s−1 at the present time. The exception is the MF radar winds, which show large station‐to‐station differences. The subject of WINDII comparisons with MF radar winds requires further study. The thermospheric O(1S) emission region is less amenable to validation, but comparisons with EISCAT radar data give excellent agreement at 170 km. A zero wind calibration has been obtained for the O(1D) emission by comparing its averaged phase with that for O(1S) on several days when alternating 1D/1S measurements were made. Several other aspects of the WINDII performance have been studied using data from on‐orbit measurements. These concern the instrument's phase stability, its pointing, its responsivity, the phase distribution in the fields of view, and the behavior of two of the interference filters. In some cases, small adjustments have been made to the characterization database used to analyze the atmospheric data. In general, the WINDII characteristics have remained very stable during the mission to date. A discussion of measurement errors is included in the paper. Further study of the instrument performance may bring improvement, but the utimate limitation for wind validation appears to be atmospheric variability and this needs to be better understood.
Measurement and speciation of gas and particulate phase organic acidity in an urban environment: 2. Speciation
Authors: Lawrence Joy , Koutrakis Petros
Published: February 2004

In the previous paper we discussed the sampling and analytical techniques used to measure the concentrations of gas and particulate phase organic acids. This paper presents the results of a field study conducted in Philadelphia, Pennsylvania, during the summer of 1992, to investigate the chemistry and origins of gas and particulate phase organic acids. The concentrations of formic acid and most of the particulate phase organic acids were found to be significantly higher during the day than at night. Organic acids constituted 5.5% of the particulate fine mass (PM2.5); sulfates, ammonium, and elemental carbon were larger components of particulate fine mass, constituting 40, 15, and 9%, respectively. Dicarboxylic acids and even‐carbon monocarboxylic acids were found to account for a large fraction of particulate weak acidity; odd‐carbon monocarboxylic acids accounted for a very small fraction. The pronounced even‐carbon preference of the monocarboxylic acid distribution suggests a biogenic origin. To investigate the origin of gas and particulate phase organic acids with regard to other species measured as part of the same field study, specific rotation factor analysis (SRFA) was applied to the daytime and nighttime concentrations of several species over the study period. During the daytime, four sources (transport, local combustion, biogenic, and photochemical) accounted for 92–99% of the particulate phase and 60–75% of the gas phase organic acids. At night, 68–87% of gas and particulate organic acids were contributed by four significant sources (transport, daytime concentration related, local combustion, and biogenic).
An atmospheric tape recorder: The imprint of tropical tropopause temperatures on stratospheric water vapor
Authors: Mote Philip W. , Rosenlof Karen H. , McIntyre Michael E. , Carr Ewan S. , Gille John C. , Holton James R. , Kinnersley Jonathan S. , Pumphrey Hugh C. , Russell James M. , Waters Joe W.
Published: February 2004

We describe observations of tropical stratospheric water vapor q that show clear evidence of large‐scale upward advection of the signal from annual fluctuations in the effective “entry mixing ratio” qE of air entering the tropical stratosphere. In other words, air is “marked,” on emergence above the highest cloud tops, like a signal recorded on an upward moving magnetic tape. We define qE as the mean water vapor mixing ratio, at the tropical tropopause, of air that will subsequently rise and enter the stratospheric “overworld” at about 400 K. The observations show a systematic phase lag, increasing with altitude, between the annual cycle in qE and the annual cycle in q at higher altitudes. The observed phase lag agrees with the phase lag calculated assuming advection by the transformed Eulerian‐mean vertical velocity of a qE crudely estimated from 100‐hPa temperatures, which we use as a convenient proxy for tropopause temperatures. The phase agreement confirms the overall robustness of the calculation and strongly supports the tape recorder hypothesis. Establishing a quantitative link between qE and observed tropopause temperatures, however, proves difficult because the process of marking the tape depends subtly on both small‐ and large‐scale processes. The tape speed, or large‐scale upward advection speed, has a substantial annual variation and a smaller variation due to the quasi‐biennial oscillation, which delays or accelerates the arrival of the signal by a month or two in the middle stratosphere. As the tape moves upward, the signal is attenuated with an e‐folding time of about 7 to 9 months between 100 and 50 hPa and about 15 to 18 months between 50 and 20 hPa, constraining possible orders of magnitude both of vertical diffusion Kz and of rates of mixing in from the extratropics. For instance, if there were no mixing in, then Kz would be in the range 0.03–0.09 m2 s−1; this is an upper bound on Kz.
An adjoint formulation of the radiative transfer method
Authors: Min Qilong , Harrison Lee C.
Published: February 2004

Radiative transfer problems may be solved “adjointly” from an observed excident radiance flux distribution backward to the incident fluxes. We describe an adjoint formulation based on the discrete ordinate radiative transfer method, with application to atmospheric radiative transfer, including effects of the surface albedo. We compare this adjoint approach with forward radiative transfer solutions for a set of synthetic cases and also with observed surface irradiance data from a multifilter rotating shadow band radiometer (MFRSR). We compute the irradiances and mean intensities at arbitrary altitudes for fixed sky conditions but varying solar zenith angles. For these cases the adjoint method is comparably accurate and markedly faster.