Gas Mixing Ratio Research Articles

Reduction of SnO2 by a Mixed Gas of Methane and Hydrogen

We investigate the reduction of SnO2 and the generation of syngas(H2, CO) using methane(CH4) and hydrogen(H2) or a mixed gas of methane and hydrogen as a reducing gas. When methane is used as a reducing gas, carbon is formed by the decomposition of methane on the reduced Sn surface, and the amount of generated carbon increases as the amount and time of the supply of methane increases. However, when hydrogen is used as a reducing gas, carbon is not generated. High purity Sn of 99.8 % and a high recovery rate of Sn of 93 % are obtained under all conditions. The effects of reducing gas species and the gas mixing ratio on the purity and recovery of Sn are not significantly different, but hydrogen is somewhat more effective in increasing the purity and recovery rate of Sn than methane. When 1 mole of methane and 1 mole of hydrogen are mixed, a product gas with an H2/CO value of 2, which is known to be most useful as syngas, is obtained.

Sensitivity Performance of Single Wall Carbon Nanotubes Gas Sensor on Silicon and Porous Silicon

Pure single walled carbon nanotubes (pure-SWCNTs) and Functionalized single walled nanotubes (F-SSWCNTs) have been utilized to the manufactured nitrogen dioxide gas sensor. CNTs films have been deposited on (n-type) silicon and porous silicon substrate by drop casting method. A porous silicon layer (PS) was prepared via electrochemical etching. The applied current density was 20 mA / cm2, and the typical electrochemical-etching time was chosen to be about 20 minutes. Upon exposure to fixed test gas mixing ratio (air: gas) NO2 at different operating temperatures, the sensitivity response results show that Pure single walled carbon nanotubes and Functionalized single walled nanotubes deposited on porous silicon have better performances than that deposited on silicon. At RT the F-SWCNTs/Ps sensitivity reaches to 36%, the response and recovery time is about 11 s and 26 s, whereas for SWCNTs/Ps the sensitivity 13.5%, the response and recovery time is about 13 s and 24 s.

Effect of gas mixing ratio on structural characteristics of titanium dioxide nanostructures synthesized by DC reactive magnetron sputtering

In this work, high-quality and highly pure titanium dioxide nanostructures were synthesized by a homemade dc closed-field unbalanced reactive magnetron sputtering system. The operation parameters of the magnetron sputtering system were optimized to prepare TiO2 nanostructures as thin films on glass substrates. These nanostructures were characterized by x-ray diffraction, atomic force microscopy and Fourier-transform infrared spectroscopy. Both anatase and rutile phases were identified. The mixing ratio of argon and oxygen (Ar:O2) gases was found very important to control the structural characteristics of the prepared nanostructures.

Optimized weighting function for IPDA lidar concerning the lower layer CO2 concentration fluctuation

Weighting function can affect the retrieval of the column gas mixing ratio of integrated path differential absorption (IPDA) lidar because it contains the vertical distribution information of the target gas. In order to optimize the wavelengths within the 1.57 um spectral band for IPDA lidar for CO2 measurement. The temperature, pressure and water vapor (TPH) sensitivity and the proportion of the weight function integration in the lower layer part to the total atmosphere layer (R) of each wavelength are calculated. The measurement errors of each wavelength are simulated with CO2 fluctuation in the lower layer. The specific wavelength with the R value of 0.6 has been found to be a stable measurement bias which does not change with fluctuations, so the R value of 0.6 is used to optimize the wavelength for measurement CO2. The simulation results show that the measurement error via wavelength is smaller than 0.05 ppm, when the TPH sensitivity is smaller than 0.95 and when R is about 0.6. This proposed method can be applicable for the further airborne or space-borne lidar development.

Study of interaction between cloud microphysics and chemistry using coupled bin microphysics and bin aqueous chemistry scheme

A bin chemistry scheme was developed to study sulfate production and the effect of aqueous chemistry on cloud microphysics in precipitating stratocumulus cloud using a 2D kinematical model. The impact of air pollution on aerosol processing was investigated by a comprehensive sensitivity study. The numerical simulations were carried out at different concentrations of condensation nuclei and trace gases of SO2, H2O2, O3 and NH3. The results show: (i) Significant amount of sulfate formed due to cloud chemistry even in less polluted atmosphere. The amount of sulfate formed due to the oxidation of S(IV) was affected less by the initial condensation nuclei (hereinafter: CN) concentration and more by the initial mixing ratio of gases in the atmosphere. The amount of sulfate staying in the atmosphere was affected by the initial CN concentration, because it impacted the efficiency of washout. (ii) The aqueous sulfate production impacts the characteristics of aerosol size distribution by increasing mean size and by increasing the concentration of the micron size aerosol particles. The change of aerosol size distribution due to sulfate production has no effect on the amount of surface precipitation if the CN concentration is low (100 cm−3), and significantly reduces accumulated surface precipitation if CN concentration is large (540 cm−3). (iii) Compared to the bin chemistry scheme the bulk chemistry scheme underestimates the sulfate production and overestimates the role of O3 in the sulfate production.

Study on the Dielectric Properties of C4F7N/N2 Mixture Under Highly Non-Uniform Electric Field

As an environment-friendly gas insulating medium, C4F7N has attracted great attention in recent years due to its excellent environmental protection and insulation performance. However, studies on the insulation performance of C4F7N/N2 gas mixture are not comprehensive at present. In this paper, the breakdown and partial discharge characteristics of the C4F7N/N2 gas mixture under highly non-uniform field were tested using the gas insulation performance test platform. The effects of gas pressure and mixing ratio on the negative partial discharge inception voltage (PDIV±), positive PDIV (PDIV−), and breakdown voltage of the gas mixture were analyzed. The engineering application potential of the C4F7N/N2 gas mixture was also discussed considering the limitation of liquefaction temperature. It is found that an increasing gas pressure or a mixing ratio can effectively improve the insulation performance of the C4F7N/N2 gas mixture. The breakdown properties of a gas mixture for a minimum operating temperature of x00B1;%at 0.3, 0.4, 0.5, and 0.6MPa can reach 63.4%, 54.6%, 49%, and 56.4% of pure SF6, respectively, and the PDIVx00B1; can reach 80.4%, 66.9%, 62.8%, and 68.8% of pure SF6, respectively. Relevant results not only reveal the influence of the mixing ratio and pressure on insulation performance of the C4F7N/N2 gas mixture, but also provide significant guidance for its engineering application.

Co-combustion of sewage sludge and coffee grounds under increased O2/CO2 atmospheres: Thermodynamic characteristics, kinetics and artificial neural network modeling

(Co-)combustion characteristics of sewage sludge (SS), coffee grounds (CG) and their blends were quantified under increased O2/CO2 atmosphere (21, 30, 40 and 60%) using a thermogravimetric analysis. Observed percentages of CG mass loss and its maximum were higher than those of SS. Under the same atmospheric O2 concentration, both higher ignition and lower burnout temperatures occurred with the increased CG content. Results showed that ignition temperature and comprehensive combustion index for the blend of 60%SS-40%CG increased, whereas burnout temperature and co-combustion time decreased with the increased O2 concentration. Artificial neural network was applied to predict mass loss percent as a function of gas mixing ratio, heating rate, and temperature, with a good agreement between the experimental and ANN-predicted values. Activation energy in response to the increased O2 concentration was found to increase from 218.91 to 347.32 kJ·mol−1 and from 218.34 to 340.08 kJ·mol−1 according to the Kissinger-Akahira-Sunose and Flynn-Wall-Ozawa methods, respectively.

Optimization of Preparation Conditions to Control Structural Characteristics of Silicon Dioxide Nanostructures Prepared by Magnetron Plasma Sputtering

In this work, highly-pure silicon oxide nanostructures were prepared by a closed-field unbalanced magnetron plasma sputtering technique. These nanostructures were characterized by Fourier-transform infrared spectroscopy, UV-visible spectroscopy, x-ray diffraction, scanning electron microscopy, energy-dispersive x-ray spectroscopy and atomic force microscopy in order to determine the optimum preparation conditions. Minimum particle size of 20 nm was determined for the samples prepared at an inter-electrode distance of 4 cm, Ar:O2 gas mixing ratio of 70:30, total gas pressure of 0.08 torr, discharge voltage of 2.5 kV, discharge current of 35 mA, anode temperature of 27 ∘C (room temperature) and cathode temperature of about 40 ∘C. These conditions are optimized to control the structural characteristics of such nanostructures and hence to satisfy certain requirements and purposes in spectroscopic and photonic applications of SiO2 nanostructures.

Using polarimetry to retrieve the cloud coverage of Earth-like exoplanets

Context. Clouds have already been detected in exoplanetary atmospheres. They play crucial roles in a planet's atmosphere and climate and can also create ambiguities in the determination of atmospheric parameters such as trace gas mixing ratios. Knowledge of cloud properties is required when assessing the habitability of a planet. Aims. We aim to show that various types of cloud cover such as polar cusps, subsolar clouds, and patchy clouds on Earth-like exoplanets can be distinguished from each other using the polarization and flux of light that is reflected by the planet. Methods. We have computed the flux and polarization of reflected starlight for different types of (liquid water) cloud covers on Earth-like model planets using the adding-doubling method, that fully includes multiple scattering and polarization. Variations in cloud-top altitudes and planet-wide cloud cover percentages were taken into account. Results. We find that the different types of cloud cover (polar cusps, subsolar clouds, and patchy clouds) can be distinguished from each other and that the percentage of cloud cover can be estimated within 10%. Conclusions. Using our proposed observational strategy, one should be able to determine basic orbital parameters of a planet such as orbital inclination and estimate cloud coverage with reduced ambiguities from the planet's polarization signals along its orbit.

Methane emissions from a Californian landfill, determined from airborne remote sensing and in situ measurements

Abstract. Fugitive emissions from waste disposal sites are important anthropogenic sources of the greenhouse gas methane (CH4). As a result of the growing world population and the recognition of the need to control greenhouse gas emissions, this anthropogenic source of CH4 has received much recent attention. However, the accurate assessment of the CH4 emissions from landfills by modeling and existing measurement techniques is challenging. This is because of inaccurate knowledge of the model parameters and the extent of and limited accessibility to landfill sites. This results in a large uncertainty in our knowledge of the emissions of CH4 from landfills and waste management. In this study, we present results derived from data collected during the research campaign COMEX (CO2 and MEthane eXperiment) in late summer 2014 in the Los Angeles (LA) Basin. One objective of COMEX, which comprised aircraft observations of methane by the remote sensing Methane Airborne MAPper (MAMAP) instrument and a Picarro greenhouse gas in situ analyzer, was the quantitative investigation of CH4 emissions. Enhanced CH4 concentrations or CH4 plumes were detected downwind of landfills by remote sensing aircraft surveys. Subsequent to each remote sensing survey, the detected plume was sampled within the atmospheric boundary layer by in situ measurements of atmospheric parameters such as wind information and dry gas mixing ratios of CH4 and carbon dioxide (CO2) from the same aircraft. This was undertaken to facilitate the independent estimation of the surface fluxes for the validation of the remote sensing estimates. During the COMEX campaign, four landfills in the LA Basin were surveyed. One landfill repeatedly showed a clear emission plume. This landfill, the Olinda Alpha Landfill, was investigated on 4 days during the last week of August and first days of September 2014. Emissions were estimated for all days using a mass balance approach. The derived emissions vary between 11.6 and 17.8 kt CH4 yr−1 with related uncertainties in the range of 14 to 45 %. The comparison of the remote sensing and in situ based CH4 emission rate estimates reveals good agreement within the error bars with an average of the absolute differences of around 2.4 kt CH4 yr−1 (±2. 8 kt CH4 yr−1). The US Environmental Protection Agency (EPA) reported inventory value is 11.5 kt CH4 yr−1 for 2014, on average 2.8 kt CH4 yr−1 (±1. 6 kt CH4 yr−1) lower than our estimates acquired in the afternoon in late summer 2014. This difference may in part be explained by a possible leak located on the southwestern slope of the landfill, which we identified in the observations of the Airborne Visible/Infrared Imaging Spectrometer – Next Generation (AVIRIS-NG) instrument, flown contemporaneously aboard a second aircraft on 1 day.

Evaluation of deep convective transport in storms from different convective regimes during the DC3 field campaign using WRF‐Chem with lightning data assimilation

AbstractDeep convective transport of surface moisture and pollution from the planetary boundary layer to the upper troposphere and lower stratosphere affects the radiation budget and climate. This study analyzes the deep convective transport in three different convective regimes from the 2012 Deep Convective Clouds and Chemistry field campaign: 21 May Alabama air mass thunderstorms, 29 May Oklahoma supercell severe storm, and 11 June mesoscale convective system (MCS). Lightning data assimilation within the Weather Research and Forecasting (WRF) model coupled with chemistry (WRF‐Chem) is utilized to improve the simulations of storm location, vertical structure, and chemical fields. Analysis of vertical flux divergence shows that deep convective transport in the 29 May supercell case is the strongest per unit area, while transport of boundary layer insoluble trace gases is relatively weak in the MCS and air mass cases. The weak deep convective transport in the strong MCS is unexpected and is caused by the injection into low levels of midlevel clean air by a strong rear inflow jet. In each system, the magnitude of tracer vertical transport is more closely related to the vertical distribution of mass flux density than the vertical distribution of trace gas mixing ratio. Finally, the net vertical transport is strongest in high composite reflectivity regions and dominated by upward transport.

A study of the combined impact of boundary layer height and near-surface meteorology on the CO diurnal cycle at a low mountaintop site using simultaneous lidar and in-situ observations

Evaluations of air pollutants and trace gas measurements over mountaintop sites and their application in inverse transport models to estimate regional scale fluxes are oftentimes challenging due to the influences associated with atmospheric transport at both local and regional scales. The objective of this study is to investigate the diurnal cycle pattern of CO mixing ratio over a low mountaintop influenced by: (1) two different convective boundary layer (CBL) regimes (shallow and deep) and associated growth rates over the mountaintop, (2) the combined effect of a deep CBL with and without diurnal wind shift, and (3) slope flows and associated air mass transport. For this purpose, we used simultaneous measurements of lidar-derived CBL heights, standard meteorological variables, and CO2 and CO mixing ratio from Pinnacles, a mountaintop monitoring site in the Appalachian Mountains. We used both water vapor and CO2 mixing ratio as tracers for upslope flow air masses. We used case studies to focus on two different scenarios of daytime CO mixing ratio variability: (1) a gradual increase in the morning with a maximum in the afternoon, and (2) a gradual decrease in the morning with a minimum in the late afternoon. The second scenario is similar to the CO variability observed atop tall towers in flat terrain.Using the lidar-derived CBL height evolution and in situ CO, CO2 and meteorological measurements over the mountaintop, we found that the CBL height dynamics, regional scale wind shift, and upslope flow air masses arriving at the mountaintop in the morning affect the CO mixing ratio variability during the remaining part of the diurnal cycle. These findings help introduce a conceptual framework that can explain and differentiate the opposite patterns (i.e. daytime increase versus daytime decrease) in the CO diurnal cycles over a mountaintop site affected by upslope flows and provide new roadmaps for monitoring and assimilating trace gas mixing ratios into applications requiring regionally-representative measurements.

Effects of the Ar and He dilution gas mixture ratio on the hardness of a-C:H films synthesized by atmospheric pressure plasma enhanced chemical vapor deposition

Hydrogenated amorphous carbon (a-C:H) films synthesized by atmospheric-pressure plasma-enhanced chemical vapor deposition (AP-PECVD) possess a low hardness because of the large amount of incorporated hydrogen. To increase the hardness of these a-C:H films, detachment of the hydrogen is accomplished using Ar ion bombardment during the deposition process. Herein, a-C:H films were deposited by AP-PECVD and the effects of varying the dilution gas mixing ratio of Ar and He on the hardness of the a-C:H films were investigated. As the Ar ratio in the mixture gas increased from 0% to 20%, the hardness of the films increased from 0.8 to 2.7 GPa. Furthermore, as the Ar ratio increased, the metastable He atoms in the plasma decreased, the intensity of the CHx peaks related to the hydrogen decreased, and the surface roughness of the films increased. These results imply that Ar ion bombardment at the film surface occurred and was caused by the Penning effect of metastable He and Ar atoms. The hardness of the a-C:H films synthesized by AP-PECVD was increased by the dilution of Ar and He gases because the hydrogen content of the films was decreased via the Ar ions generated by the Ar and He mixture gases.

Chemical Reaction on Etched TaNO Thin Film as O2 Content Varies in CF4/Ar Gas Mixing Plasma

In this work, we investigated the etching characteristics of TaNO thin films and the selectivity of TaNO to SiO2 in an O2/CF4/Ar inductively coupled plasma (ICP) system. The maximum etch rate of TaNO thin film was 297.1 nm/min at a gas mixing ratio of O2/CF4/Ar (6:16:4 sccm). At the same time, the etch rate was measured as a function of the etching parameters, such as the RF power, DC-bias voltage, and process pressure. X-ray photoelectron spectroscopy analysis showed the efficient destruction of the oxide bonds by the ion bombardment, as well as the accumulation of low volatile reaction products on the etched surface. Based on these data, the ion-assisted chemical reaction was proposed as the main etch mechanism for the CF4-containing plasmas.

Breakdown characteristics of CF3I-N2 gas mixtures in a needle-plate geometry

The breakdown voltages in a needle-plate geometry have been measured by 50 Hz power frequency tests for the CF3I-N2 gas mixtures (5–30% CF3I) over the gas pressure from 0.1 to 0.3 MPa. The influence of different conditions on the breakdown performance is investigated. The synergistic effect of CF3I-N2 gas mixtures is verified from the respect of breakdown voltage. Moreover, the behavior of the gas mixtures in highly divergent fields is characterized by a pressure range of corona stabilization, which can explain the relation of the breakdown strength to gas pressure and mixing ratio. A comparison to the theoretical breakdown voltages in uniform electric field shows that the breakdown strength reduces with the rising non-uniform coefficient of electric field at relatively short gap distance. Furthermore, the sensitivity of the insulating ability to divergent field is weakened by the increasing CF3I ratio.

A new Differential Optical Absorption Spectroscopy instrument to study atmospheric chemistry from a high-altitude unmanned aircraft

Abstract. Observations of atmospheric trace gases in the tropical upper troposphere (UT), tropical tropopause layer (TTL), and lower stratosphere (LS) require dedicated measurement platforms and instrumentation. Here we present a new limb-scanning Differential Optical Absorption Spectroscopy (DOAS) instrument developed for NASA's Global Hawk (GH) unmanned aerial system and deployed during the Airborne Tropical TRopopause EXperiment (ATTREX). The mini-DOAS system is designed for automatic operation under unpressurized and unheated conditions at 14–18 km altitude, collecting scattered sunlight in three wavelength windows: UV (301–387 nm), visible (410–525 nm), and near infrared (900–1700 nm). A telescope scanning unit allows selection of a viewing angle around the limb, as well as real-time correction of the aircraft pitch. Due to the high altitude, solar reference spectra are measured using diffusors and direct sunlight. The DOAS approach allows retrieval of slant column densities (SCDs) of O3, O4, NO2, and BrO with relative errors similar to other aircraft DOAS systems. Radiative transfer considerations show that the retrieval of trace gas mixing ratios from the observed SCD based on O4 observations, the most common approach for DOAS measurements, is inadequate for high-altitude observations. This is due to the frequent presence of low-altitude clouds, which shift the sensitivity of the O4 SCD into the lower atmosphere and make it highly dependent on cloud coverage. A newly developed technique that constrains the radiative transfer by comparing in situ and DOAS O3 observations overcomes this issue. Extensive sensitivity calculations show that the novel O3-scaling technique allows the retrieval of BrO and NO2 mixing ratios at high accuracies of 0.5 and 15 ppt, respectively. The BrO and NO2 mixing ratios and vertical profiles observed during ATTREX thus provide new insights into ozone and halogen chemistry in the UT, TTL, and LS.

Observations of Atmospheric Methane and Carbon Dioxide Mixing Ratios: Tall-Tower or Mountain-Top Stations?

Mountain-top observations of greenhouse gas mixing ratios may be an alternative to tall-tower measurements for regional scale source and sink estimation. To investigate the equivalence or limitations of a mountain-top site as compared to a tall-tower site, we used the unique opportunity of comparing in situ measurements of methane ( $$\hbox {CH}_{4}$$ ) and carbon dioxide ( $$\hbox {CO}_{2}$$ ) mixing ratios at a mountain top (986 m above sea level, a.s.l.) with measurements from a nearby (distance 28.4 km) tall tower, sampled at almost the same elevation (1009 m a.s.l.). Special attention was given to, (i) how local wind statistics and greenhouse gas sources and sinks at the mountain top influence the observations, and (ii) whether mountain-top observations can be used as for those from a tall tower for constraining regional greenhouse gas emissions. Wind statistics at the mountain-top site are clearly more influenced by local flow systems than those at the tall-tower site. Differences in temporal patterns of the greenhouse gas mixing ratios observed at the two sites are mostly related to the influence of local sources and sinks at the mountain-top site. Major influences of local sources can be removed by applying a statistical filter ( $$5{\mathrm{th}}$$ percentile) or a filter that removes periods with unfavourable flow conditions. In the best case, the bias in mixing ratios between the mountain-top and the tall-tower sites after the application of the wind filter was $${-}0.0005\pm 0.0010$$ ppm for methane (September, 0000–0400 UTC) and $$0.11\pm 0.18$$ ppm for $$\hbox {CO}_{2}$$ (February, 1200–1600 UTC). Temporal fluctuations of atmospheric $$\hbox {CH}_{4}$$ and $$\hbox {CO}_{2}$$ mixing ratios at both stations also showed good agreement (apart from $$\hbox {CO}_{2}$$ during summertime) as determined by moving bi-weekly Pearson correlation coefficients (up to 0.96 for $$\hbox {CO}_{2}$$ and 0.97 for $$\hbox {CH}_{4}$$ ). When only comparing mixing ratios minimally influenced by local sources (low bias and high correlation coefficients), our measurements indicate that mountain-top observations are comparable to tall-tower observations.

A study on plasma parameters in Ar/SF6 inductively coupled plasma

Sulfur hexafluoride (SF6) gas or Ar/SF6 mixing gas is widely used in plasma processes. However, there are a little experimental studies with various external parameters such as gas pressure and mixing ratio. In this work, a study of the plasma parameters by changing the gas mixing ratio was done in an Ar/SF6 inductively coupled plasma from the measurement of the electron energy distribution function. At a low gas pressure, as the mixing ratio of SF6 gas increased at a fixed inductively coupled plasma (ICP) power, the electron density decreased and the electron temperature increased, while they were not changed drastically. At a high gas pressure, a remarkable increase in the electron temperature was observed with the decrease in the electron density. These variations are due to the electron loss reactions such as the electron attachment. It was also found that at a fixed ICP power, the negative ion creation with the diluted SF6 gas can change the discharge mode transition from an inductive mode to a capacitive mode at the high gas pressure. The electron attachment reactions remove the low energy electrons and change the mean electron energy towards higher energies with diluting SF6 gas at high pressure. The measured results were compared with the simplified global model, and the global model is in relatively good agreement with the measured plasma parameters except for the result in the case of the large portion of SF6 gas at the high pressure and the capacitive mode, which causes strong negative ion formation by the electron attachment reactions.

Ten-year chemical signatures associated with long-range transport observed in the free troposphere over the central North Atlantic

Ten-year observations of trace gases at Pico Mountain Observatory (PMO), a free troposphere site in the central North Atlantic, were classified by transport patterns using the Lagrangian particle dispersion model, FLEXPART. The classification enabled identifying trace gas mixing ratios associated with background air and long- range transport of continental emissions, which were defined as chemical signatures. Comparison between the chemical signatures revealed the impacts of natural and anthropogenic sources, as well as chemical and physical processes during long transport,on air composition in the remote North Atlantic. Transport of North American anthropogenic emissions(NA-Anthro) and summertime wildfire plumes (Fire) significantly enhanced CO and O3 at PMO. Summertime CO enhancements caused by NA-Anthro were found to have been decreasing by a rate of 0.67 ± 0.60 ppbv/year in the ten-year period, due possibly to reduction of emissions in North America. Downward mixing from the upper troposphere and stratosphere due to the persistent Azores-Bermuda anticyclone causes enhanced O3 and nitrogen oxides. The d[O3]/d [CO] value was used to investigate O3 sources and chemistry in different transport patterns. The transport pattern affected by Fire had the lowest d [O3]/d [CO], which was likely due to intense CO production and depressed O3 production in wildfire plumes. Slightly enhanced O3 and d [O3]/d [CO] were found in the background air, suggesting that weak downward mixing from the upper troposphere is common at PMO. Enhancements of both butane isomers were found during upslope flow periods, indicating contributions from local sources. The consistent ratio of butane isomers associated with the background air and NA-anthro implies no clear difference in the oxidation rates of the butane isomers during long transport. Based on observed relationships between non-methane hydrocarbons, the averaged photochemical age of the air masses at PMO was estimated to be 11 ± 4 days.

Impact of future climate policy scenarios on air quality and aerosol-cloud interactions using an advanced version of CESM/CAM5: Part I. model evaluation for the current decadal simulations

A version of the Community Earth System Model modified at the North Carolina State University (CESM-NCSU) is used to simulate the current and future atmosphere following the representative concentration partway scenarios for stabilization of radiative forcing at 4.5 W m−2 (RCP4.5) and radiative forcing of 8.5 W m−2 (RCP8.5). Part I describes the results from a comprehensive evaluation of current decadal simulations. Radiation and most meteorological variables are well simulated in CESM-NCSU. Cloud parameters are not as well simulated due in part to the tuning of model radiation and general biases in cloud variables common to all global chemistry-climate models. The concentrations of most inorganic aerosol species (i.e., SO42-, NH4+, and NO3−) are well simulated with normalized mean biases (NMBs) typically less than 20%. However, some notable exceptions are European NH4+, which is overpredicted by 33.0–42.2% due to high NH3 emissions and irreversible coarse mode condensation, and Cl−, that is negatively impacted by errors in emissions driven by wind speed and overpredicted HNO3. Carbonaceous aerosols are largely underpredicted following the RCP scenarios due to low emissions of black carbon, organic carbon, and anthropogenic volatile compounds in the RCP inventory and efficient wet removal. This results in underpredictions of PM2.5 and PM10 by 6.4–55.7%. The column mass abundances are reasonably well simulated. Larger biases occur in surface mixing ratios of trace gases in CESM-NCSU, likely due to numerical diffusion from the coarse grid spacing of the CESM-NCSU simulations or errors in the magnitudes and vertical structure of emissions. This is especially true for SO2 and NO2. The mixing ratio of O3 is overpredicted by 38.9–76.0% due to the limitations in the O3 deposition scheme used in CESM and insufficient titration resulted from large underpredictions in NO2. Despite these limitations, CESM-NCSU reproduces reasonably well the current atmosphere in terms of radiation, clouds, meteorology, trace gases, aerosols, and aerosol-cloud interactions, making it suitable for future climate simulations.