Variations In Atmospheric Composition Research Articles

Seasonal Variation of Biogenic and Anthropogenic VOCs in a Semi-Urban Area Near Sydney, Australia

Volatile organic compounds (VOCs) play a key role in the formation of ozone and secondary organic aerosol, the two most important air pollutants in Sydney, Australia. Despite their importance, there are few available VOC measurements in the area. In this paper, we discuss continuous GC-MS measurements of 10 selected VOCs between February (summer in the southern hemisphere) and June (winter in the southern hemisphere) of 2019 in a semi-urban area between natural eucalypt forest and the Sydney metropolitan fringe. Combined, isoprene, methacrolein, methyl-vinyl-ketone, α-pinene, p-cymene, eucalyptol, benzene, toluene xylene and tri-methylbenzene provide a reasonable representation of variability in the total biogenic VOC (BVOC) and anthropogenic VOC (AVOC) loading in the area. Seasonal changes in environmental conditions were reflected in observed BVOC concentrations, with a summer peak of 8 ppb, dropping to approximately 0.1 ppb in winter. Isoprene, and its immediate oxidation products methacrolein (MACR) and methyl-vinyl-ketone (MVK), dominated BVOC concentrations during summer and early autumn, while monoterpenes comprised the larger fraction during winter. Temperature and solar radiation drive most of the seasonal variation observed in BVOCs. Observed levels of isoprene, MACR and MVK in the atmosphere are closely related with variations in temperature and photosynthetically active radiation (PAR), but chemistry and meteorology may play a more important role for the monoterpenes. Using a nonlinear model, temperature explains 51% and PAR 38% of the isoprene, MACR and MVK variation. Eucalyptol dominated the observed monoterpene fraction (contributing ~75%), with p-cymene (20%) and α-pinene (5%) also present. AVOCs maintain an average concentration of ~0.4 ppb, with a slight decrease during autumn–winter. The low AVOC concentrations observed indicate a relatively small anthropogenic influence, generally occurring when (rare) northerly winds transport Sydney emissions to the measurement site. The site is influenced by domestic, commercial and vehicle AVOC emissions. Our observed AVOC concentrations can be explained by the seasonal changes in meteorology and the emissions in the area as listed in the NSW emissions inventory and thereby act as an independent validation of this inventory. We conclude that the variations in atmospheric composition observed during the seasons are an important variable to consider when formulating air pollution control policies over Sydney given the influence of biogenic sources during summer, autumn and winter.

Updated tropospheric chemistry reanalysis and emission estimates, TCR-2, for 2005–2018

Abstract. This study presents the results from the Tropospheric Chemistry Reanalysis version 2 (TCR-2) for the period 2005–2018 at 1.1∘ horizontal resolution obtained from the assimilation of multiple updated satellite measurements of ozone, CO, NO2, HNO3, and SO2 from the OMI, SCIAMACHY, GOME-2, TES, MLS, and MOPITT satellite instruments. The reanalysis calculation was conducted using a global chemical transport model MIROC-CHASER and an ensemble Kalman filter technique that optimizes both chemical concentrations of various species and emissions of several precursors, which was efficient for the correction of the entire tropospheric profile of various species and its year-to-year variations. Comparisons against independent aircraft, satellite, and ozonesonde observations demonstrate the quality of the reanalysis fields for numerous key species on regional and global scales, as well as for seasonal, yearly, and decadal scales, from the surface to the lower stratosphere. The multi-constituent data assimilation brought the model vertical profiles and interhemispheric gradient of OH closer to observational estimates, which was important in improving the description of the oxidation capacity of the atmosphere and thus vertical profiles of various species. The evaluation results demonstrate the capability of the chemical reanalysis to improve understanding of the processes controlling variations in atmospheric composition, including long-term changes in near-surface air quality and emissions. The estimated emissions can be employed for the elucidation of detailed distributions of the anthropogenic and biomass burning emissions of co-emitted species (NOx, CO, SO2) in all major regions, as well as their seasonal and decadal variabilities. The data sets are available at https://doi.org/10.25966/9qgv-fe81 (Miyazaki et al., 2019a).

Seasonal Variations in Atmospheric Composition as Measured in Gale Crater, Mars

AbstractThe Sample Analysis at Mars (SAM) instrument onboard the Mars Science Laboratory Curiosity rover measures the chemical composition of major atmospheric species (CO2, N2, 40Ar, O2, and CO) through a dedicated atmospheric inlet. We report here measurements of volume mixing ratios in Gale Crater using the SAM quadrupole mass spectrometer, obtained over a period of nearly 5 years (3 Mars years) from landing. The observation period spans the northern summer of MY 31 and solar longitude (LS) of 175° through spring of MY 34, LS = 12°. This work expands upon prior reports of the mixing ratios measured by SAM QMS in the first 105 sols of the mission. The SAM QMS atmospheric measurements were taken periodically, with a cumulative coverage of four or five experiments per season on Mars. Major observations include the seasonal cycle of CO2, N2, and Ar, which lags approximately 20–40° of LS behind the pressure cycle driven by CO2 condensation and sublimation from the winter poles. This seasonal cycle indicates that transport occurs on faster timescales than mixing. The mixing ratio of O2 shows significant seasonal and interannual variability, suggesting an unknown atmospheric or surface process at work. The O2 measurements are compared to several parameters, including dust optical depth and trace CH4 measurements by Curiosity. We derive annual mean volume mixing ratios for the atmosphere in Gale Crater: CO2 = 0.951 (±0.003), N2 = 0.0259 (±0.0006), 40Ar = 0.0194 (±0.0004), O2 = 1.61 (±0.09) x 10‐3, and CO = 5.8 (±0.8) x 10‐4.

Variations in atmospheric composition over Northern Eurasia regions under weather and climate anomalies associated with atmospheric blocking events

Changes in the composition of the atmosphere associated with the atmospheric blocking events were analyzed using the measurements of ozone, water vapor, methane, formaldehyde, carbon monoxide, nitrogen dioxide, as well as aerosol optical characteristics from the satellite instruments OMI, MLS, AIRS, MODIS and MOPITT as well as ground-based, balloon and NCEP/NCAR reanalysis data. The changes in atmospheric composition associated with pyrogenic, biogenic and soil emissions of aerosol and gas constituents as well as the changes due to the regional peculiarities of the large-scale atmospheric dynamics are discussed.

Thermospheric Expansion Associated With Dust Increase in the Lower Atmosphere on Mars Observed by MAVEN/NGIMS

AbstractWe present for the first time the dramatic variations in atmospheric composition and density at high altitudes from 170 to 220 km in Mars' neutral thermosphere in response to dust increases in the lower atmosphere, observed by the in situ Neutral Gas Ion Mass Spectrometer onboard the Mars Atmosphere and Volatile EvolutioN satellite. The observations reveal that CO2, Ar, N2, CO, and O densities all increase up to ~200% compared to the longer‐term running median densities. The density increases are seen throughout this altitude region, and the relative variations are seen to be stronger at higher altitudes. Density increases indicating the solar extreme ultraviolet influence are also seen. This study is consistent with that during increased dust load, the whole atmosphere expands and rises, and other processes may also be involved. The results agree with the general circulation model predictions, providing observational evidence for how dust increases affect different atmospheric species in the thermosphere.

Tracking elevated pollution layers with a newly developed hyperspectral Sun/Sky spectrometer (4STAR): Results from the TCAP 2012 and 2013 campaigns

AbstractTotal columnar water vapor (CWV), nitrogen dioxide (NO2), and ozone (O3) are derived from a newly developed, hyperspectral airborne Sun‐sky spectrometer (4STAR) for the first time during the two intensive phases of the Two‐Column Aerosol Project (TCAP) in summer 2012 and winter 2013 aboard the DOE G‐1 aircraft. We compare results with coincident measurements. We find 0.045 g/cm2 (4.2%) negative bias and 0.28 g/cm2 (26.3%) root‐mean‐square difference (RMSD) in water vapor layer comparison with an in situ hygrometer and an overall RMSD of 1.28 g/m3 (38%) water vapor amount in profile by profile comparisons, with differences distributed evenly around zero. RMSD for O3 columns average to 3%, with a 1% negative bias for 4STAR compared with the Ozone Measuring Instrument along aircraft flight tracks for 14 flights during both TCAP phases. Ground‐based comparisons with Pandora spectrometers at the Goddard Space Flight Center, Greenbelt, Maryland, showed excellent agreement between the instruments for both O3 (1% RMSD and 0.1% bias) and NO2 (17.5% RMSD and −8% bias). We apply clustering analysis of the retrieved products as a case study during the TCAP summer campaign to identify variations in atmospheric composition of elevated pollution layers and demonstrate that combined total column measurements of trace gas and aerosols can be used to define different pollution layer sources, by comparing our results with trajectory analysis and in situ airborne miniSPLAT (single‐particle mass spectrometer) measurements. Our analysis represents a first step in linking sparse but intense in situ measurements from suborbital campaigns with total column observations from space.

Rainfall measurement from the opportunistic use of an Earth–space link in the Ku band

Abstract. The present study deals with the development of a low-cost microwave device devoted to the measurement of average rain rates observed along Earth–satellite links, the latter being characterized by a tropospheric path length of a few kilometres. The ground-based power measurements, which are made using the Ku-band television transmissions from several different geostationary satellites, are based on the principle that the atmospheric attenuation produced by rain encountered along each transmission path can be used to determine the path-averaged rain rate. This kind of device could be very useful in hilly areas where radar data are not available or in urban areas where such devices could be directly placed in homes by using residential TV antenna. The major difficulty encountered with this technique is that of retrieving rainfall characteristics in the presence of many other causes of received signal fluctuation, produced by atmospheric scintillation, variations in atmospheric composition (water vapour concentration, cloud water content) or satellite transmission parameters (variations in emitted power, satellite pointing). In order to conduct a feasibility study with such a device, a measurement campaign was carried out over a period of five months close to Paris. The present paper proposes an algorithm based on an artificial neural network, used to identify dry and rainy periods and to model received signal variability resulting from effects not related to rain. When the altitude of the rain layer is taken into account, the rain attenuation can be inverted to obtain the path-averaged rain rate. The rainfall rates obtained from this process are compared with co-located rain gauges and radar measurements taken throughout the full duration of the campaign, and the most significant rainfall events are analysed.

Mapping the Instability Domains of GW Vir Stars in the Effective Temperature–Surface Gravity Diagram

We present the results of a detailed stability study of models of GW Vir pulsators. These are extremely hot, evolved, and compact stars that are on their way to the white dwarf cooling phase and that show multiperiodic luminosity variations due to gravity-mode pulsational instabilities. Our nonadiabatic survey confirms that cyclic ionization of carbon and oxygen is at the origin of the GW Vir phenomenon. We find that the extent of the instability domain in the log g-Teff plane is a strong function of the C and O content in the envelopes of these stars. Given that GW Vir stars show important variations in atmospheric composition from one object to another, this implies that the notion of a blue edge for the GW Vir instability domain is necessarily a fuzzy concept. We investigate the effects of varying the total mass, of adding hydrogen, and of changing the metallicity. We summarize our results in the form of extensive stability maps in the log g-Teff diagram and produce tables and graphs showing the expected ranges of excited periods under various conditions.

Utilizing stable isotope abundances of lichens to monitor environmental change

Reported field observations, laboratory studies and transplant experiments confirm that lichens are affected by pollutants. The ubiquitous nature of lichens and their susceptibility to the environment suggest that their response to variations in atmospheric composition might provide a useful means for monitoring environmental quality. Through such monitoring, the detection of abnormal levels of defined pollutants in the atmosphere would be an indicator of the need for remedial action before dramatic evidence of environmental damage becomes apparent. An additional advantage would be that previously unrecognized pollution sources affecting lichens and the wider environment might be detected. As lichens have important ecological and economic roles in our society, recognition of lichen communities at risk would be an associated benefit.The stable isotope abundance of carbon in the lichen Cladia aggregata has been investigated in a study relating these values with known levels of selected pollutants in the region within a 200-km radius of Sydney, Australia. A total of 129 samples of the sterile and fertile forms of the lichen was obtained from 36 different sites. There was an 8‰ range in the δ13C values of these samples of whole lichen. Small effects on δ13C values in the lichen, of less than ±1‰, were found to be associated with distance from pollution source, slope of the substrate site, humidity, altitude and number of rain days at the sampling site. The effects of the natural parameters tend to cancel out. A statistically significant negative correlation between δ13C values in the whole lichen and atmospheric sulphur dioxide concentrations was found. This is consistent with the known destructive effect of SO2 on lichens. δ13C values in lichens in wet environments, in the presence of high SO2 concentrations, were more negative than in samples from drier sites. The direction of this relationship is contrary to that observed in laboratory studies by other workers. An explanation of this effect may relate to an increase in carboxylation resistance resulting from damage to chlorophyll and cell structure by SO2, which over-rides an inverse effect of CO2 resistance that increases with wetting of the lichens. The predictive reliability of the graphical tool formulated from these data requires the accumulation of data for atmospheric SO2 concentrations localized to sampling sites, followed by further testing.

Narrowband-to-broadband albedo conversion for glacier ice and snow: equations based on modeling and ranges of validity of the equations

In this paper, we propose equations for narrowband-to-broadband (NTB) albedo conversion for glacier ice and snow for four types of satellite sensors: thematic mapper (TM), advanced very high resolution radiometer (AVHRR), moderate resolution imaging spectroradiometer (MODIS), and multi-angle imaging spectroradiometer (MISR). We do this on the basis of spectral albedos and incident spectral irradiances generated with radiative-transfer models of the (sub-)surface (a two-stream model) and the atmosphere, respectively. First, we establish equations for reference values of atmospheric components and the surface elevation. These equations describe measurements with root-mean-square differences of ∼0.016. We then show that the “reference equations” also perform well when total ozone and aerosol optical depth are changed with respect to the reference. The negative effect of humidity and elevation variations on the performance of the equations can be eliminated by adding a correction term. We argue that narrowband albedos are much less sensitive to variations in the incident spectral irradiance than broadband albedos. Hence, our conclusions about the effects of variations in atmospheric composition and elevation are also valid for equations for NTB conversion proposed in other papers.

Cd/Ca in Planktonic Foraminifera of the Glacial Southern Ocean

Since the industrial revolution, 200 years ago, atmospheric carbon dioxide levels have risen by 90 ppmV, an amount equalling the natural variation between the last glacial maximum and pre-industrial values. To predict the fate and influence of anthropogenic carbon dioxide, it is vital to understand the natural controls on the glacial-interglacial variations in atmospheric composition. The biological pump is known to be an important draw-down of carbon dioxide today due to the complete removal of nutrients from the euphotic zone of most surface waters and regeneration at depth. An exception exists in the Southern Ocean today, where the surface waters have high phosphate concentrations indicating incomplete removal of the nutrients either due to very rapid upwelling rates or iron limitation. There is huge potential for glacial carbon dioxide draw-down if the efficiency of the biological pump had been enhanced in the glacial Southern Ocean. Particle proxies suggest that export productivity increased in the glacial subantarctic Southern Ocean (1) but there has been no clear evidence of a lowering of the glacial surface-water nutrients (2). fil3c in planktonic foraminifera has been found to be unreliable as a nutrient tracer in surface waters due to a number of factors such as susceptibility to isotopic fractionation during air-sea exchange (3). Cd/Ca in foraminifera, a reliable deep-water nutrient tracer, has been uncalibrated for surface waters and is often present at levels too low for determination by existing methods. We have developed a new isotope dilution, mass-spectrometric method for low-level determination of Cd/Ca in foraminifera which has allowed reliable and accurate planktonic analyses to be made. We have investigated the application of Cd/ Ca in planktonic foraminifera for the reconstruction of past surface water phosphate levels. Down-core records of Cd/Ca in G.Bulloides covering the last complete glacial cycle have been obtained from a latitudinal transect of cores spanning the present day Subtropical Convergence Zone (SCZ), at approximately 40~ and the Antarctic Polar Front (APF), at approximately 50~ in the Indian Ocean sector of the Southern Ocean. In each core there is a striking correlation between the Cd/Ca and the 5180 of G.Bulloides over the last glacial cycle indicating low surface water nutrient levels during the glacials and high nutrient levels during the interglacials. The greatest reduction in nutrient levels occurs in the subantarctic zone of the Southern Ocean, with little change south of the APF, consistent with the export productivity conclusions. There are two possible explanations for this glacial lowering of surface water nutrients. Firstly the rate of upwelling remains constant but the efficiency of nutrient removal is increased, possibly by iron fertilization due to an increased atmospheric dust fallout in glacial times. Secondly, the glacial Southern Ocean water column became stratified with a stable thermocline altowing the surface water productivity to deplete the nutrients without constant replenishment from upwelling. It is important to distinguish between these two mechanisms as each has a differing potential for glacial draw-down of atmospheric carbon dioxide. A simple box-model following some of the concepts in (4) has been run to resolve which of these two mechanisms is more consistent with the new surface water nutrient data and the existing export productivity conclusions.

Electron auroral excitation efficiencies and intensity ratios

Ground‐based auroral observations with a meridian‐scanning photometer and all‐sky camera were made at Rabbit Lake, Saskatchewan, Canada, simultaneously with nearby HILAT satellite passes during six winter periods near new moon from 1984 to 1986. Eight passes were selected in which HILAT overflew auroras visible from Rabbit Lake. Auroral intensity measurements made at Rabbit Lake were corrected for proton aurora and nightglow and compared with HILAT electron flux measurements at 800 km. The excitation efficiency for the 4278‐Å auroral emission by electron precipitation was found to be (0.29±0.08) kR/(erg/cm² s). Excitation efficiencies for 5577‐Å emission of (1.73±0.51) kR/(erg/cm² s) and (1.23±0.44) kR/(erg/cm² s) were measured on different days in auroras excited by 1.8‐keV and 3.1‐keV Maxwellian precipitation during moderate geomagnetic disturbance. After small night‐to‐night variations in atmospheric composition indicated by the MSIS‐86 model atmosphere were accounted for, the magnetic zenith column intensity ratio 6300/4278 was found to depend on the electron characteristic energy Eo approximately as 6300/4278 ∼ 3.3 Eo−2.1 for characteristic energies of a few keV. The 5577/4278 ratio was found to decrease by about 40% from 1 to 5 keV characteristic energy. These Results pertain mostly to weak auroras (I(5577 Å) = 2–6 kR). Most of these new measurements agree fairly well with previous results of other workers, but the two 5577‐Å excitation efficiencies and the decreasing 5577/4278 intensity ratio show that the green line excitation efficiency varies appreciably even for small changes in the precipitating electron spectrum and atmospheric composition. Published calculations of the auroral 6300/4278 and 5577/4278 ratios versus characteristic energy are compared with our measurements. The magnitude and variation of the 5577/4278 ratios are consistent with roughly 60% of green line emission resulting from O(¹S) excitation by N2(A) energy transfer.

Photostimulated oxidation of magnetite: 1. Kinetics and alteration phase identification

It has been demonstrated that magnetite (Fe3O4) becomes oxidized upon exposure to ultraviolet and visible radiation in O2-bearing atmospheres. X ray diffraction and diffuse reflectance studies of the oxidation product indicate that hematite (α-Fe2O3) is the principal reaction phase, although some maghemite (γ-Fe2O3) may also be produced. A set of kinetic constraints on the photostimulated oxidation mechanism has been determined by measuring the response of the reaction rate to variations in atmospheric composition and pressure, incident spectral radiation intensity distribution, temperature, and the amounts and types of adsorbed species present. The reaction rate is proportional to (pO2)1/2, for O2 partial pressures between 1.0 × 10−4 torr and 1.0 × 102 torr; to (PT)−2 for total atmospheric pressures between 6 and 800 torr; to (Φ0.350)3/2 for the incident photon flux at λ = 0.350 μ ranging between 6.6 × 1014 and 2.8 × 1019 photons cm−2 sec−1 A−1; and the rate responds in a complex way to variations in the quantity of H2O adsorbed to the grain surfaces. The reaction rate is apparently not sensitive to variations in the partial pressures of CO2, CO, N2, Ar, or H2O, to the temperature, or to the amounts of Ar, N2, CO2, or CO adsorbed to the grain surfaces. An attempt to determine the effect of particle size on the reaction rate was unsuccessful. The results indicate that recent experimental evidence for ‘lunar bleaching’ may be spurious. Photostimulated oxidation may occur naturally on Mars, however.