CO2 Mixing Ratios Research Articles

Seven years of observational atmospheric CO2 at a maritime site in northernmost Japan and its implications

Surface atmospheric CO2 mixing ratio reflects both natural fluctuation of the carbon cycle and the effect of anthropogenic activities. Long-term observation of atmospheric CO2 forms the basis for model simulations of the carbon cycle both in the straightforward and the inversion ways. Atmospheric CO2 has been measured on Rishiri Island (45.1°N, 141.2°E) in the western North Pacific since May 2006. We report the first 7-year temporal CO2 variations from diurnal to inter-annual scales and the implications on the vegetation phenology. Diurnally, an obvious cycle appeared as a minimum in the afternoon and maximum at midnight in the summer months, caused by local vegetation. Seasonally, the maximum CO2 concentration appeared around the beginning of April, while the minimum appeared around the middle of August. This seasonal variation implied the natural cycle of terrestrial biological activities of the boreal forest, mostly in the east Eurasia. A mean growing season length of ~126days was estimated. In the period from 2007 to 2012, the peak-to-peak amplitude increased until 2009 and decreased thereafter, with a mean value of 19.7ppm. Inter-annually, atmospheric CO2 is increasing by a mean growth rate of 2.1ppmyear−1. The study provides invaluable dataset and useful information to better understand the carbon cycle and its interaction with climate change.

Variations of carbon monoxide in the martian lower atmosphere

Our observations of variations of CO on Mars by means of the ground-based spatially-resolved high-resolution spectroscopy (Krasnopolsky, V.A. [2003]. J. Geophys. Res. 108(E2), 5010; Krasnopolsky, V.A. [2007]. Icarus 190, 93–102) have been significantly improved using the 13CO lines near 4148cm−1 and the CO2 lines near 4570cm−1. These lines are of optimal strength, of low sensitivity to variations of temperature, and covered by the ATMOS solar spectrum that makes it possible to use the synthetic spectra technique for retrieval of CO and CO2 to get CO mixing ratios. The CO2 line strengths from Toth et al. (2008) were also essential to improve accuracy of the results.The 13CO/CO ratio of 1.023 times the terrestrial carbon isotope ratio was calculated using the known 13CO2/CO2=1.046 in the martian atmosphere (Webster, C.R., et al. [2013]. Science 341, 260–263), the photo-induced isotope fractionation (Miller, C.E., Yung, Y.L. [2000]. J. Geophys. Res. 105(D23), 29039–29051) in the CO2 photolysis, and isotope fractionation in the reaction between CO and OH (Feilberg, K.L., Johnson, M.S., Nielsen, C.J. [2005]. Phys. Chem. Chem. Phys. 7, 2318–2323).The observations were conducted at LS=60°, 89°, 110°, and 145° and extend over the maximum of CO in the southern hemisphere during the northern summer. The CO mixing ratio was observed to be constant over the 55°S–90°N latitudinal range to within 7%, for each observed LS period. Therefore our observations show that the enrichment of incondensable gases by condensation of CO2 in the southern polar regions does not significantly extend to the middle and low latitudes. This behavior agrees with the Mars Climate Database (Lefevre, F., Forget, F. [2009]. Nature 460, 720–722), whereas most other observations exhibit much larger latitudinal gradients and seasonal variations. Our measurements do not show the CO depletion at high northern latitudes predicted by MCD of ∼20% at LS≈60–150° and observed as much stronger by MRO/CRISM (Toigo, A.D., et al. [2013]. J. Geophys. Res. 118E, 89–104).The retrieved global and annually mean CO abundance is equal to 700ppm on Mars, which is also smaller than many recent results by a factor of ∼1.4.

Low-power, open-path mobile sensing platform for high-resolution measurements of greenhouse gases and air pollutants

A low-power mobile sensing platform has been developed with multiple open-path gas sensors to measure the ambient concentrations of greenhouse gases and air pollutants with high temporal and spatial resolutions over extensive spatial domains. The sensing system consists of four trace gas sensors including two custom quantum cascade laser-based open-path sensors and two LICOR open-path sensors to measure CO2, CO, CH4, N2O, NH3, and H2O mixing ratios simultaneously at 10 Hz. In addition, sensors for meteorological and geolocation data are incorporated into the system. The system is powered by car batteries with a low total power consumption (~200 W) and is easily transportable due to its low total mass (35 kg). Multiple measures have been taken to ensure robust performance of the custom, open-path sensors located on top of the vehicle where the optics are exposed to the harsh on-road environment. The mobile sensing system has been integrated and installed on top of common passenger vehicles and participated in extensive field campaigns (>400 h on-road time with >18,000 km total distance) in both the USA and China. The simultaneous detection of multiple trace gas species makes the mobile sensing platform a unique and powerful tool to identify and quantify different emission sources through mobile mapping.

Differential absorption lidar for volcanic CO(2) sensing tested in an unstable atmosphere.

Motivated by the need for an extremely durable and portable instrument to quantify volcanic CO(2) we have produced a corresponding differential absorption lidar (DIAL). It was tested on a volcano (Vulcano, Italy), sensing a non-uniform volcanic CO(2) signal under turbulent atmospheric conditions. The measured CO(2) mixing ratio trend agrees qualitatively well but quantitatively poorly with a reference CO(2) measurement. The disagreement is not in line with the precision of the DIAL determined under conditions that largely exclude atmospheric effects. We show evidence that the disagreement is mainly due to atmospheric turbulence. We conclude that excluding noise associated with atmospheric turbulence, as commonly done in precision analysis of DIAL instruments, may largely underestimate the error of measured CO(2) concentrations in turbulent atmospheric conditions. Implications for volcanic CO(2) sensing with DIAL are outlined.

An estimation of the <sup>18</sup>O / <sup>16</sup>O ratio of UT/LMS ozone based on artefact CO in air sampled during CARIBIC flights

Abstract. An issue of O3-driven artefact production of O3 in the upper troposphere/lowermost stratosphere (UT/LMS) air analysed in the CARIBIC-1 project is being discussed. By confronting the CO mixing and isotope ratios obtained from different analytical instrumentation, we (i) reject natural/artificial sampling and mixing effects as possible culprits of the problem, (ii) ascertain the chemical nature and quantify the strength of the contamination, and (iii) demonstrate successful application of the isotope mass-balance calculations for inferring the isotope composition of the contamination source. The δ18O values of the latter indicate that the oxygen is very likely being inherited from O3. The δ13C values hint at reactions of trace amounts of organics with stratospheric O3 that could have yielded the artificial CO. While the exact contamination mechanism is not known, it is clear that the issue pertains only to the earlier (first) phase of the CARIBIC (Civil Aircraft for the Regular Investigation of the atmosphere Based on an Instrument Container) project. Finally, estimated UT/LMS ozone δ18O values are lower than those observed in the stratosphere within the same temperature range, suggesting that higher pressures (240–270 hPa) imply lower isotope fractionation controlling the local δ18O(O3) value.

Characteristics of Black Carbon Aerosol during the Chinese Lunar Year and Weekdays in Xi’an, China

Black carbon (BC) aerosol plays an important role in climate forcing. The net radiative effect is strongly dependent on the physical properties of BC particles. A single particle soot photometer and a carbon monoxide analyser were deployed during the Chinese Lunar Year (CLY) and on weekdays at Xi’an, China, to investigate the characteristics of refractory black carbon aerosol (rBC). The rBC mass on weekdays (8.4 μg·m−3) exceeds that during the CLY (1.9 μg·m−3), presumably due to the lower anthropogenic emissions during the latter. The mass size distribution of rBC shows a primary mode peak at ~205 nm and a small secondary mode peak at ~102-nm volume-equivalent diameter assuming 2 g·cm−3 in void-free density in both sets of samples. More than half of the rBC cores are thickly coated during the CLY (fBC = 57.5%); the percentage is slightly lower (fBC = 48.3%) on weekdays. Diurnal patterns in rBC mass and mixing state differ for the two sampling periods, which are attributed to the distinct anthropogenic activities. The rBC mass and CO mixing ratios are strongly correlated with slopes of 0.0070 and 0.0016 μg·m−3·ppbv−1 for weekdays and the CLY, respectively.

Tunable diode laser measurements of hydrothermal/volcanic CO<sub>2</sub> and implications for the global CO<sub>2</sub> budget

Abstract. Quantifying the CO2 flux sustained by low-temperature fumarolic fields in hydrothermal/volcanic environments has remained a challenge, to date. Here, we explored the potential of a commercial infrared tunable laser unit for quantifying such fumarolic volcanic/hydrothermal CO2 fluxes. Our field tests were conducted between April 2013 and March 2014 at Nea Kameni (Santorini, Greece), Hekla and Krýsuvík (Iceland) and Vulcano (Aeolian Islands, Italy). At these sites, the tunable laser was used to measure the path-integrated CO2 mixing ratios along cross sections of the fumaroles' atmospheric plumes. By using a tomographic post-processing routine, we then obtained, for each manifestation, the contour maps of CO2 mixing ratios in the plumes and, from their integration, the CO2 fluxes. The calculated CO2 fluxes range from low (5.7 ± 0.9 t d−1; Krýsuvík) to moderate (524 ± 108 t d−1; La Fossa crater, Vulcano). Overall, we suggest that the cumulative CO2 contribution from weakly degassing volcanoes in the hydrothermal stage of activity may be significant at the global scale.

Evidence for a three-phase sequence during Heinrich Stadial 4 using a multiproxy approach based on Greenland ice core records

Abstract. Glacial climate was characterised by two types of abrupt events. Greenland ice cores record Dansgaard–Oeschger events, marked by abrupt warming in-between cold, stadial phases. Six of these stadials appear related to major Heinrich events (HEs), identified from ice-rafted debris (IRD) and large excursions in carbon- and oxygen-stable isotopic ratios in North Atlantic deep sea sediments, documenting major ice sheet collapse events. This finding has led to the paradigm that glacial cold events are induced by the response of the Atlantic Meridional Overturning Circulation to such massive freshwater inputs, supported by sensitivity studies conducted with climate models of various complexities. These models also simulate synchronous Greenland temperature and lower-latitude hydrological changes. To investigate the sequence of events between climate changes at low latitudes and in Greenland, we provide here the first 17O-excess record from a Greenland ice core during Dansgaard–Oeschger events 7 to 13, encompassing H4 and H5. Combined with other ice core proxy records, our new 17O-excess data set demonstrates that stadials are generally characterised by low 17O-excess levels compared to interstadials. This can be interpreted as synchronous change of high-latitude temperature and lower-latitude hydrological cycle (relative humidity at the oceanic source of evaporation or change in the water mass trajectory/recharge) and/or an influence of local temperature on 17O-excess through kinetic effect at snow formation. As an exception from this general pattern, stadial 9 consists of three phases, characterised first by Greenland cooling during 550 ± 60 years (as shown by markers of Greenland temperature δ18O and δ15N), followed by a specific lower-latitude fingerprint as identified from several proxy records (abrupt decrease in 17O-excess, increase in CO2 and methane mixing ratio, heavier δD-CH4 and δ18Oatm), lasting 740 ± 60 years, itself ending approximately 390 ± 50 years prior to abrupt Greenland warming. We hypothesise that this lower-latitude signal may be the fingerprint of Heinrich event 4 in Greenland ice cores. The proposed decoupling between stable cold Greenland temperature and low-latitude climate variability identified for stadial 9 provides new targets for benchmarking climate model simulations and testing mechanisms associated with millennial variability.

Chemistry–Climate Interactions of Stratospheric and Mesospheric Ozone in EMAC Long-Term Simulations with Different Boundary Conditions for CO2, CH4, N2O, and ODS

To evaluate future climate change in the middle atmosphere and the chemistry–climate interaction of stratospheric ozone, we performed a long-term simulation from 1960 to 2050 with boundary conditions from the Intergovernmental Panel on Climate Change A1B greenhouse gas scenario and the World Meteorological Organization Ab halogen scenario using the chemistry–climate model ECHAM5/MESSy Atmospheric Chemistry (EMAC). In addition to this standard simulation we performed five sensitivity simulations from 2000 to 2050 using the rerun files of the simulation mentioned above. For these sensitivity simulations we used the same model setup as in the standard simulation but changed the boundary conditions for carbon dioxide (CO2), methane (CH4), nitrous oxide (N2O), and ozone-depleting substances (ODS). In the first sensitivity simulation we fixed the mixing ratios of CO2, CH4, and N2O in the boundary conditions to the amounts for 2000. In each of the four other sensitivity simulations we fixed the boundary conditions of only one of CO2, CH4, N2O, or ODS to the year 2000.In our model simulations the future evolution of greenhouse gases leads to significant cooling in the stratosphere and mesosphere. Increasing CO2 mixing ratios make the largest contributions to this radiative cooling, followed by increasing stratospheric CH4, which also forms additional H2O in the upper stratosphere and mesosphere. Increasing N2O mixing ratios makes the smallest contributions to the cooling. The simulated ozone recovery leads to warming of the middle atmosphere.In the EMAC model the future development of ozone is influenced by several factors. 1) Cooler temperatures lead to an increase in ozone in the upper stratosphere. The strongest contribution to this ozone production is cooling due to increasing CO2 mixing ratios, followed by increasing CH4. 2) Decreasing ODS mixing ratios lead to ozone recovery, but the contribution to the total ozone increase in the upper stratosphere is only slightly higher than the contribution of the cooling by greenhouse gases. In the polar lower stratosphere a decrease in ODS is mainly responsible for ozone recovery. 3) Higher NOx and HOx mixing ratios due to increased N2O and CH4 lead to intensified ozone destruction, primarily in the middle and upper stratosphere, from additional NOx; in the mesosphere the intensified ozone destruction is caused by additional HOx. In comparison to the increase in ozone due to decreasing ODS, ozone destruction caused by increased NOx is of similar importance in some regions, especially in the middle stratosphere. 4) In the stratosphere the enhancement of the Brewer-Dobson circulation leads to a change in ozone transport. In the polar stratosphere increased downwelling leads to additional ozone in the future, especially at high northern latitudes. The dynamical impact on ozone development is higher at some altitudes in the polar stratosphere than the ozone increase due to cooler temperatures. In the tropical lower stratosphere increased residual vertical upward transport leads to a decrease in ozone.

High-precision dual-inlet IRMS measurements of the stable isotopes of CO<sub>2</sub> and the N<sub>2</sub>O / CO<sub>2</sub> ratio from polar ice core samples

Abstract. An important constraint on mechanisms of past carbon cycle variability is provided by the stable isotopic composition of carbon in atmospheric carbon dioxide (δ13C-CO2) trapped in polar ice cores, but obtaining very precise measurements has proven to be a significant analytical challenge. Here we describe a new technique to determine the δ13C of CO2 at very high precision, as well as measuring the CO2 and N2O mixing ratios. In this method, ancient air is extracted from relatively large ice samples (~400 g) with a dry-extraction "ice grater" device. The liberated air is cryogenically purified to a CO2 and N2O mixture and analyzed with a microvolume-equipped dual-inlet IRMS (Thermo MAT 253). The reproducibility of the method, based on replicate analysis of ice core samples, is 0.02‰ for δ13C-CO2 and 2 ppm and 4 ppb for the CO2 and N2O mixing ratios, respectively (1σ pooled standard deviation). Our experiments show that minimizing water vapor pressure in the extraction vessel by housing the grating apparatus in a ultralow-temperature freezer (−60 °C) improves the precision and decreases the experimental blank of the method to −0.07 ± 0.04‰. We describe techniques for accurate calibration of small samples and the application of a mass-spectrometric method based on source fragmentation for reconstructing the N2O history of the atmosphere. The oxygen isotopic composition of CO2 is also investigated, confirming previous observations of oxygen exchange between gaseous CO2 and solid H2O within the ice archive. These data offer a possible constraint on oxygen isotopic fractionation during H2O and CO2 exchange below the H2O bulk melting temperature.

Ground-based aerosol characterization during the South American Biomass Burning Analysis (SAMBBA) field experiment

Abstract. This paper investigates the physical and chemical characteristics of aerosols at ground level at a site heavily impacted by biomass burning. The site is located near Porto Velho, Rondônia, in the southwestern part of the Brazilian Amazon rainforest, and was selected for the deployment of a large suite of instruments, among them an Aerosol Chemical Speciation Monitor. Our measurements were made during the South American Biomass Burning Analysis (SAMBBA) field experiment, which consisted of a combination of aircraft and ground-based measurements over Brazil, aimed to investigate the impacts of biomass burning emissions on climate, air quality, and numerical weather prediction over South America. The campaign took place during the dry season and the transition to the wet season in September/October 2012. During most of the campaign, the site was impacted by regional biomass burning pollution (average CO mixing ratio of 0.6 ppm), occasionally superimposed by intense (up to 2 ppm of CO), freshly emitted biomass burning plumes. Aerosol number concentrations ranged from ~1000 cm−3 to peaks of up to 35 000 cm−3 (during biomass burning (BB) events, corresponding to an average submicron mass mean concentrations of 13.7 μg m−3 and peak concentrations close to 100 μg m−3. Organic aerosol strongly dominated the submicron non-refractory composition, with an average concentration of 11.4 μg m−3. The inorganic species, NH4, SO4, NO3, and Cl, were observed, on average, at concentrations of 0.44, 0.34, 0.19, and 0.01 μg m−3, respectively. Equivalent black carbon (BCe) ranged from 0.2 to 5.5 μg m−3, with an average concentration of 1.3 μg m−3. During BB peaks, organics accounted for over 90% of total mass (submicron non-refractory plus BCe), among the highest values described in the literature. We examined the ageing of biomass burning organic aerosol (BBOA) using the changes in the H : C and O : C ratios, and found that throughout most of the aerosol processing (O : C ≅ 0.25 to O : C ≅ 0.6), no remarkable change is observed in the H : C ratio (~1.35). Such a result contrasts strongly with previous observations of chemical ageing of both urban and Amazonian biogenic aerosols. At higher levels of processing (O : C > 0.6), the H : C ratio changes with a H : C / O : C slope of −0.5, possibly due to the development of a combination of BB (H : C / O : C slope = 0) and biogenic (H : C /O :C slope =−1) organic aerosol (OA). An analysis of the ΔOA /ΔCO mass ratios yields very little enhancement in the OA loading with atmospheric processing, consistent with previous observations. These results indicate that negligible secondary organic aerosol (SOA) formation occurs throughout the observed BB plume processing, or that SOA formation is almost entirely balanced by OA volatilization. Positive matrix factorization (PMF) of the organic aerosol spectra resulted in three factors: fresh BBOA, aged BBOA, and low-volatility oxygenated organic aerosol (LV-OOA). Analysis of the diurnal patterns and correlation with external markers indicates that during the first part of the campaign, OA concentrations are impacted by local fire plumes with some chemical processing occurring in the near-surface layer. During the second part of the campaign, long-range transport of BB plumes above the surface layer, as well as potential SOAs formed aloft, dominates OA concentrations at our ground-based sampling site. This manuscript describes the first ground-based deployment of the aerosol mass spectrometry at a site heavily impacted by biomass burning in the Amazon region, allowing a deeper understanding of aerosol life cycle in this important ecosystem.

The effect of Lyman α radiation on mini-Neptune atmospheres around M stars: application to GJ 436b

Mini-Neptunes orbiting M stars are a growing population of known exoplanets. Some of them are located very close to their host star, receiving large amounts of UV radiation. Many M stars emit strong chromospheric emission in the H i Lyman α line (Lyα) at 1215.67 Å, the brightest far-UV emission line. We show that the effect of incoming Lyα flux can significantly change the photochemistry of mini-Neptunes’ atmospheres. We use GJ 436b as an example, considering different metallicities for its atmospheric composition. For solar composition, H2O-mixing ratios show the largest change because of Lyα radiation. H2O absorbs most of this radiation, thereby shielding CH4, whose dissociation is driven mainly by radiation at other far-UV wavelengths (∼1300 Å). H2O photolysis also affects other species in the atmosphere, including H, H2, CO2, CO, OH and O. For an atmosphere with high metallicity, H2O- and CO2-mixing ratios show the biggest change, thereby shielding CH4. Direct measurements of the UV flux of the host stars are important for understanding the photochemistry in exoplanets’ atmospheres. This is crucial, especially in the region between 1 and 10−6 bars, which is the part of the atmosphere that generates most of the observable spectral features.

Atmospheric hydrogen peroxide and Eoarchean iron formations

It is widely accepted that photosynthetic bacteria played a crucial role in Fe(II) oxidation and the precipitation of iron formations (IF) during the Late Archean-Early Paleoproterozoic (2.7-2.4 Ga). It is less clear whether microbes similarly caused the deposition of the oldest IF at ca. 3.8 Ga, which would imply photosynthesis having already evolved by that time. Abiological alternatives, such as the direct oxidation of dissolved Fe(II) by ultraviolet radiation may have occurred, but its importance has been discounted in environments where the injection of high concentrations of dissolved iron directly into the photic zone led to chemical precipitation reactions that overwhelmed photooxidation rates. However, an outstanding possibility remains with respect to photochemical reactions occurring in the atmosphere that might generate hydrogen peroxide (H2 O2 ), a recognized strong oxidant for ferrous iron. Here, we modeled the amount of H2 O2 that could be produced in an Eoarchean atmosphere using updated solar fluxes and plausible CO2 , O2 , and CH4 mixing ratios. Irrespective of the atmospheric simulations, the upper limit of H2 O2 rainout was calculated to be <10(6) molecules cm(-2) s(-1) . Using conservative Fe(III) sedimentation rates predicted for submarine hydrothermal settings in the Eoarchean, we demonstrate that the flux of H2 O2 was insufficient by several orders of magnitude to account for IF deposition (requiring ~10(11) H2 O2 molecules cm(-2) s(-1) ). This finding further constrains the plausible Fe(II) oxidation mechanisms in Eoarchean seawater, leaving, in our opinion, anoxygenic phototrophic Fe(II)-oxidizing micro-organisms the most likely mechanism responsible for Earth's oldest IF.

Titan’s atmosphere as observed by Cassini/VIMS solar occultations: CH4, CO and evidence for C2H6 absorption

We present an analysis of the VIMS solar occultations dataset, which allows us to extract vertically resolved information on the characteristics of Titan’s atmosphere between ∼100 and 700km with a vertical resolution of ∼10km. After a series of data treatment procedures to correct problems in pointing stability and parasitic light, 4 occultations out of 10 are retained. This sample covers different seasons and latitudes of Titan. The transmittances show clearly the evolution of the haze, with the detection of the detached layer at ∼310km in September 2011 at mid-northern latitudes. Through the inversion of the transmission spectra with a line-by-line radiative transfer code we retrieve the vertical distribution of CH4 and CO mixing ratio. For methane inversion we use its 1.4, 1.7 and 2.3μm bands. The first two bands are always in good agreement and yield an average stratospheric abundance of 1.28±0.08%, after correcting for forward-scattering effects, with no significant differences between the occultations. This is significantly less than the value of 1.48% obtained by the GCMS/Huygens instrument. We find that the 2.3μm band cannot be used for the extraction of methane abundance because it is blended with other absorptions, not included in our atmospheric model. The analysis of the residual spectra after the inversion shows that such additional absorptions are present through a great part of the VIMS wavelength range. We attribute many of these bands, including the one at 2.3μm, to gaseous ethane, whose near-infrared spectrum is not well modeled yet. Ethane also contributes significantly to the strong absorption at 3.2–3.5μm that was previously attributed only to C–H stretching bands from aerosols. Ethane bands may affect the surface windows too, especially at 2.7μm. Other residual bands are generated by stretching modes of C–H, C–C and C–N bonds. In addition to the C–H stretch from aliphatic hydrocarbons at 3.4μm, we detect a strong and narrow absorption at 3.28μm which we tentatively attribute to the presence of PAHs in the stratosphere. C–C and C–N stretching bands are possibly present between 4.3 and 4.5μm. Finally, we obtain the CO mixing ratio between 70 and 170km, through the inversion of its 4.7μm band. The average result of 46±16ppm is in good agreement with previous studies.

Surface gas pollutants in Lhasa, a highland city of Tibet – current levels and pollution implications

Abstract. Through several years of development, the city of Lhasa has become one of the most populated and urbanized areas on the highest plateau in the world. In the process of urbanization, current and potential air quality issues have been gradually concerned. To investigate the current status of air pollution in Lhasa, various gas pollutants including NOx, CO, SO2, and O3, were continuously measured from June 2012 to May 2013 at an urban site (29.40° N, 91.08° E, 3650 m a.s.l.). The seasonal variations of primary gas pollutants exhibited a peak from November to January with a large variability. High mixing ratios of primary trace gases almost exclusively occurred under low wind speed and showed no distinct dependence on wind direction, implying local urban emissions to be predominant. A comparison of NO2, CO, and SO2 mixing ratios in summer between 1998 and 2012 indicated a significant increase in emissions of these gas pollutants and a change in their intercorrelations, as a result of a substantial growth in the demand of energy consumption using fossil fuels instead of previously widely used biomass. The pronounced diurnal double peaks of primary trace gases in all seasons suggested automobile exhaust to be a major emission source in Lhasa. The secondary gas pollutant O3 displayed an average diurnal cycle of a shallow flat peak for about 4–5 h in the afternoon and a minimum in the early morning. Nighttime O3 was sometimes completely consumed by the high level of NOx. Seasonally, the variations of O3 mixing ratios displayed a low valley in winter and a peak in spring. In autumn and winter, transport largely contributed to the observed O3 mixing ratios, given its dependence on wind speed and wind direction, while in spring and summer photochemistry played an important role. A more efficient buildup of O3 mixing ratios in the morning and a higher peak in the afternoon was found in summer 2012 than in 1998. An enhancement in O3 mixing ratios would be expected in the future and more attention should be given to O3 photochemistry in response to increasing precursor emissions in this area.

Temporal characteristics of atmospheric CO2 in urban Nanjing, China

Although China is a big carbon dioxide (CO2) emitter, in situ measurements of atmospheric CO2 are sparse in urban China. The mixing ratio of carbon dioxide (CO2) and its influencing factors in urban Nanjing were investigated in this study, from the 18th of January to the 31st of December 2011. The annual average mixing ratio of CO2 was 406.5±20.0ppmv over the study period. The signal analysis using the fast Fourier transform (FFT) algorithm showed that CO2 had different cycles as a result of multiple controlling factors. The seasonal and intra-seasonal fluctuations of CO2 were mainly caused by the terrestrial biospheric uptake and emission and atmospheric oscillation. The weekly variation of CO2 was largely influenced by traffic volume. The diurnal cycle of CO2 presented a bimodal pattern in winter (DJF) probably due to the rush hour emissions. The seasonal mean CO2/CO correlation slope varied from 0.024ppmv/ppbv to 0.029ppmv/ppbv, comparable to the fossil fuel combustion emission ratio. The diurnal pattern of CO2/CO was irregular, indicating random anthropogenic emissions in an urban area. Firework setting was a large source of CO2 during the Spring Festival holiday. The backward trajectories by the HYSPLIT model showed that the local anthropogenic emissions contributed the most to the high CO2 mixing ratio in the urban area.

The Taihu Eddy Flux Network: An Observational Program on Energy, Water, and Greenhouse Gas Fluxes of a Large Freshwater Lake

Lakes are an important component of the climate system. They provide moisture for precipitation, buffer temperature variations, and contribute to regional atmospheric carbon budgets. This article describes an eddy covariance (EC) mesonet on Lake Taihu, a large (area 2400 km2) and shallow (depth 2 m) lake situated in the heavily populated Yangtze River Delta, China. The mesonet consists of five lake sites, representing different biological attributes and wind–wave patterns, and a land site near the lake shore. Common to all the sites are standard EC instruments for measurement of the momentum, sensible heat, water vapor, and CO2 flux. One site is also equipped with laser-based analyzers for precise measurement of the CO2, CH4, and H2O mixing ratios and their isotopic compositions. To the authors' best knowledge, this is the first lake eddy flux mesonet. Early results reveal evidence of biological and pollution controls on the surface–air fluxes of energy, momentum, and greenhouse gases across the lake. The...

Analysis of diurnal variability of atmospheric halocarbons and CFC replacements to imply emission strength and sources at an urban site of Lukang in central Taiwan

Hourly atmospheric measurements of halocarbons and chlorofluorocarbon (CFC) replacements were conducted at an urban site of Lukang, Changhua, in central Taiwan from May to August, 2013. The temporal distribution of different groups of halocarbons in the Lukang urban atmosphere, including chlorofluorocarbons (CFCs), Chlorodifluoromethane (HCFC-22), Bromochlorodifluoromethane (Halon-1211), and other chlorinated compounds, is presented and discussed. The concentrations (mixing ratios) of HCFC-22, Dichlorodifluoromethane (CFC-12), Halon-1211, Trichlorofluoromethane (CFC-11), Dichloromethane (CH2Cl2), and Trichloroethylene (TCE) were enhanced with respect to the local background levels; the atmospheric mixing ratio of carbon tetrachloride (CCl4) was slightly higher than its local background level; on the other hand, 1,1,2-Trichlorotrifluoroethane (CFC-113) was relatively uniform and not very different from background atmospheric level in non-urban areas. Among these compounds, HCFC-22, Halon-1211 and the halogenated compounds, CH2Cl2 and TCE, used as solvents were strongly enhanced. The average mixing ratio of Halon-1211 was higher than the local background of ∼4.5 ppt by ∼60% although Halon-1211 production had been phased out by 1996.Hourly average mixing ratios of halocarbons (HCFC-22, CFC-12, Halon-1211, CFC-11, CH2Cl2, and TCE) illustrated a distinct diurnal cycle characterized with a pattern of elevated mixing ratio and large mixing ratio variability amplitude at night relative to that in daytime. Although emission sources of these halocarbons were complex, hourly average mixing ratios for most of these high variability halocarbons peaked at ∼5:00 AM when the hourly average wind speed reached the minimum value of the day; by contrast, the hourly average mixing ratio of CO peaked at ∼8:30 AM when the ambient atmospheric wind condition was strongly influenced by sea breezes during the traffic rush hours. This phenomenon revealed that meteorological factors predominated the distribution of halocarbon mixing ratio in the urban atmosphere and the traffic emission of CFC-12 derived from old vehicles manufactured before 1994 was insignificant to the CFC-12 mixing ratio in the urban atmosphere. The meteorological condition of nighttime atmospheric temperature inversion and low wind speed facilitated the accumulation of terrestrial airborne pollutants near the ground; consequently the hourly average mixing ratios at night were higher than those in daytime by up to ∼2% (CFC-11), ∼7% (CFC-12), ∼75% (HCFC-22), ∼72% (Halon-1211), ∼280% (CH2Cl2), and ∼155% (TCE).

CO and byproduct formation during CO2 reduction in dielectric barrier discharges

The dissociation of CO2 and the formation of CO, O3, and O2 were studied in a dielectric barrier discharge (DBD) at atmospheric pressure by means of ex-situ infrared absorption spectroscopy. CO mixing ratios of 0.1%–4.4% were determined for specific injected energies between 0.1 and 20 eV per molecule (0.3–70 kJ/l). A lower limit of the gas temperature of 320–480 K was estimated from the wall temperature of the quartz reactor as measured with an infrared camera. The formation of CO in the DBD could be described as function of the total number of transferred charges during the residence time of the gas in the active plasma zone. An almost stoichiometric CO:O2 ratio of 2:1 was observed along with a strongly temperature dependent O3 production up to 0.075%. Although the ideal range for an efficient CO2 dissociation in plasmas of 1 eV per molecule for the specific injected energy was covered, the energy efficiency remained below 5% for all conditions. The present results indicate a reaction mechanism which is initiated by electron impact processes followed by charge transfer reactions and non-negligible surface enhanced O and CO recombination. While electron-driven CO2 dissociation is relatively energy inefficient by itself, fast O recombination and the low gas temperatures inhibit the synergistic reuse of atomic oxygen in a secondary CO2 + O dissociation step.

How stratospheric are deep stratospheric intrusions?

Abstract. Preliminary attempts of quantifying the stratospheric ozone contribution in the observations at the Zugspitze summit (2962 m a.s.l.) next to Garmisch-Partenkirchen in the German Alps had yielded an approximate doubling of the stratospheric fraction of the Zugspitze ozone during the time period 1978 to 2004. These investigations had been based on data filtering by using low relative humidity (RH) and elevated 7Be as the criteria for selecting half-hour intervals of ozone data representative of stratospheric intrusion air. To quantify the residual stratospheric component in stratospherically influenced air masses, however, the mixing of tropospheric air into the stratospheric intrusion layers must be taken into account. In fact, the dewpoint mirror instrument at the Zugspitze summit station rarely registers RH values lower than 10% in stratospheric air intrusions. Since 2007 a programme of routine lidar sounding of ozone, water vapour and aerosol has been conducted in the Garmisch-Partenkirchen area. The lidar results demonstrate that the intrusion layers are drier by roughly one order of magnitude than indicated in the in situ measurements. Even in thin layers RH values clearly below 1% have frequently been observed. These thin, undiluted layers present an important challenge for atmospheric modelling. Although the ozone values never reach values typical of the lower-stratosphere it becomes, thus, obvious that, without strong wind shear or convective processes, mixing of stratospheric and tropospheric air must be very slow in most of the free troposphere. As a consequence, the analysis the Zugspitze data can be assumed to be more reliable than anticipated. Finally, the concentrations of Zugspitze carbon monoxide rarely drop inside intrusion layers and normally stay clearly above full stratospheric values. This indicates that most of the CO, and thus the intrusion air mass, originates in the shallow "mixing layer" around the thermal tropopause. The CO mixing ratio in these descending layers between 1990 and 2004 exhibits a slightly positive trend indicating some Asian influence on the lowermost stratosphere in the high-latitude source region of most intrusions reaching the station.