Surface CO2 Concentrations Research Articles

Time variations in the concentration of pollutants in the atmosphere over Moscow and estimation of their emissions

Data on the surface NO, NO2, CO, SO2, CH4, and PM10 concentrations measured at 46 stations from 2005 to 2014 in Moscow have been used in studying the characteristic features of their distribution over the city area and their time variations. Both seasonal and interannual variations in pollutant concentrations, as well as their 10-year trends, are closely related with variations in the urban infrastructure and weather conditions. The weekly cycle of the pollutants has been analyzed. Its largest amplitude is 18.9 ± 5.6% for NO. For CO, NO2, and PM10, the amplitudes amount to 9.3 ± 3.2%, 13.6 ± 2.8%, and 10.9 ± 5.5%, respectively. The weekly variations in CH4 and SO2 concentrations are not significant for such large-scale territorial averaging. The emission fluxes of CO, NOx, SO2, and CH4 and their integral emissions from the Moscow megacity have been estimated from multiyear measurements of their surface concentrations and both vertical air-temperature and wind stratifications. During 2005—2014, the annual integral emissions of CO, NOx, and CH4 decreased with a rate of -1.9 ± 0.3, -1.7 ± 0.4, and -7.8 ± 3.1 %·yr-1, respectively, and that of SO2 increased with a rate of 3.3 ± 2.3 %·yr-1. The means of integral annual pollutant emissions from Moscow differ slightly from those for other world megacities. The CO emissions coincide with their EDGAR v4.2 inventory values interpolated to the territory of Moscow. However, the EDGAR v4.2 values of NOx, SO2 and CH4 significantly exceed their calculated values.

Interaction between carbon dioxide emissions and eutrophication in a drinking water reservoir: A three-dimensional ecological modeling approach

We developed a three-dimensional model to study the dynamics of carbon dioxide (CO2) emission from a subtropical drinking water reservoir. The quantitative effects of dissolved CO2 concentration on phytoplankton growth were coupled in an inorganic carbon module. Water quality monitoring was carried out to calibrate and validate the model. The simulated surface CO2 concentrations showed no significant difference between seasons (p>0.05). Regarding the spatial distribution, high CO2 concentrations were observed in the inflow and dam regions (p<0.05). Four scenarios of different atmospheric CO2 pressures and eutrophic levels were simulated to test the following hypotheses: (1) eutrophication will reverse the carbon budgets in reservoir systems and (2) rising CO2 levels will increase phytoplankton biomass. The results showed that water quality improvements will promote the emission of CO2 into the atmosphere. Simultaneously, the elevated CO2 in the air will stimulate algal biomass, especially in nutrient-rich systems. The systematic analysis of carbon cycling revealed the different internal transformation rates under different scenarios and showed that 32% of carbon was removed via CO2 emission and carbon burial. The interaction provides a novel direction to understand the feedback loops between aquatic ecosystems and increasing CO2 pressure in the future.

Self-Inhibitory Electron Transfer of the Co(III)/Co(II)-Complex Redox Couple at Pristine Carbon Electrode.

Applications of conducting carbon materials for highly efficient electrochemical energy devices require a greater fundamental understanding of heterogeneous electron-transfer (ET) mechanisms. This task, however, is highly challenging experimentally, because an adsorbing carbon surface may easily conceal its intrinsic reactivity through adventitious contamination. Herein, we employ nanoscale scanning electrochemical microscopy (SECM) and cyclic voltammetry to gain new insights into the interplay between heterogeneous ET and adsorption of a Co(III)/Co(II)-complex redox couple at the contamination-free surface of electron-beam-deposited carbon (eC). Specifically, we investigate the redox couple of tris(1,10-phenanthroline)cobalt(II), Co(phen)32+, as a promising mediator for dye-sensitized solar cells and redox flow batteries. A pristine eC surface overlaid with KCl is prepared in vacuum, protected from contamination in air, and exposed to an ultrapure aqueous solution of Co(phen)32+ by the dissolution of the protective KCl layer. We employ SECM-based nanogap voltammetry to quantitatively demonstrate that Co(phen)32+ is adsorbed on the pristine eC surface to electrostatically self-inhibit outer-sphere ET of nonadsorbed Co(phen)33+ and Co(phen)32+. Strong electrostatic repulsion among Co(phen)32+ adsorbates is also demonstrated by SECM-based nanogap voltammetry and cyclic voltammetry. Quantitatively, self-inhibitory ET is characterized by a linear decrease in the standard rate constant of Co(phen)32+ oxidation with a higher surface concentration of Co(phen)32+ at the formal potential. This unique relationship is consistent not with the Frumkin model of double layer effects, but with the Amatore model of partially blocked electrodes as extended for self-inhibitory ET. Significantly, the complicated coupling of electron transfer and surface adsorption is resolved by combining nanoscale and macroscale voltammetric methods.

Study on carbon dioxide atmospheric distribution over the Southwest Indian Ocean islands using satellite data: Part 1 – Climatology and seasonal results

The forests of the Southwest Indian Ocean (SWIO) islands States are large carbon sinks. Rapid population growth in these islands is responsible for deforestation, which in turn is the main source of carbon dioxide (CO2) emissions. This study is divided into two parts: The present study (Part 1) describes the seasonal vertical and surface spatial distribution of CO2 over the SWIO islands and the temporal variation of surface CO2 concentrations using data measured by the Tropospheric Emission Spectrometer (TES) on board the Aura Satellite. The CO2 hotspots over these islands were identified and assessed to determine if they were associated with deforestation and forest degradation anthropogenic activities. Areas of minimum or low CO2 atmospheric loading were also identified, and investigated to determine if they coincided with strong sink areas. Atmospheric CO2 concentration was building-up from summer to spring. The spatial extent of CO2 hotspots was found to increase from summer to spring. Over the study region, semi-permanent stable layers at 700 hPa and 500 hPa were shown to separate the troposphere into three layers of CO2. Furthermore, surface CO2 levels over all the study areas were found to be increasing during the period of the investigation. Part 2 of this study demonstrates the influence of meteorology and associated air transport on atmospheric CO2 distribution over the study region.

Review on ocean acidification and carbon cycling in the Arctic Ocean

The uptake of anthropogenic CO2 by the ocean decreases seawater pH and carbonate mineral aragonite saturation state ( Ω arag), a process known as Ocean Acidification (OA). This could be detrimental to marine organisms and ecosystems. It is well known that the Arctic Ocean is a Bellwether for prospective changes in the global ocean acidification. Over the past two decades, global warming and climate change have caused rapid changes in the Arctic, especially in the western Arctic Ocean. These changes include rapid sea ice retreat and increases in sea surface temperatures, Pacific water inflow, freshwater storage, primary production, and surface CO2 concentrations. Projected climate change processes are thought to amplify OA in the Arctic Ocean, and absorption of CO2 and carbon burial in the arctic ocean makes it more rapid and significant in response to climate change than other basins. Based on the advantages of high-level China-US cooperation over the past decade, thorough and complete work of data collection, sorting and analysis for the 7 Chinese Arctic Research Expedition (CHINARE-Arc) cruises from 1999 to 2016 with the icebreaker R/V Xuelong, and a supplement of other US database collected during 1994−2011 which have provided opportunities for Chinese and U.S. scientists to investigate the status and changes of the Arctic Ocean. In this review, we first summarize the climate and environmental change in the arctic over the past 20 years. These changes have important implications for the carbon cycle and ocean acidification. With respect to carbon cycle, we summarize influences of rapidly changing sea-ice and growing Pacific inflow on the absorption of atmospheric CO2 in the Chukchi Sea, the response of deep-ocean carbon sequestration (continental shelf pump) to the changing environment, and to summarize a hypothesis of low-low-high variation trend in sea surface water p CO2 along a decreasing ice-cover gradient across three different zones in the western Arctic Ocean under a rapid sea ice melting scenario in the summer. In particular, high resolution survey of sea surface CO2 level (high p CO2) were reported across the Canada Basin, showing a great increase over earlier observations. Contrary to the current prediction, the Arctic Ocean basin would not become a large atmospheric CO2 sink under ice-free conditions. In addition, we review the rate and scale of ocean acidification in the western Arctic Ocean and evaluate links to environmental and climate change over the past two decades. Our new research indicates that, between the 1990s and 2010, acidified waters has increased in the upper 250 m from 5% to 31% of the total area north of 70°N. The Arctic Ocean is the first open ocean where we see such a large-scale increase in acidification, more than two times faster than that observed in the Pacific or Atlantic oceans. Tracer data and model simulations suggest that increased Pacific Winter Water (PWW), driven by retreating sea ice and anomalous circulation patterns in the summer season, is primarily responsible for this OA expansion. Finally, the future changes of carbon cycling and ocean acidification in the context of climate change are outlined.

Global warming, grain production and its efficiency: Case study of major grain production region

Historical records and multiple researches have indicated that there is a close connection between carbon dioxide and surface temperature. Climate change and its impacts on agriculture, especially grain production, is one of the major challenges for food security and sustainable development. From the perspective of natural flow, climate change directly affects plant growth via water circulation, such as droughts and floods. Although the covariation of surface temperature and CO2 concentration will to some extent benefit crop photosynthesis, grain production may fluctuate according to the grain market, which is also affected by its erratic provisioning. We then determine how climate change affects grain production and efficiency using an input distance function and technical inefficiency model. First, we discover a significant relationship between surface temperature and grain production, although this impact is marginal; the coefficient is 0.0037 in the estimated model. Second, we find that surface temperature influences grain production not only through its photosynthesis but also its production efficiency in major grain production areas. And grain production efficiency is in a decreasing trend from 2000 to 2010, the average efficiency in 2010 is 0.75 on the whole. Third, there is a large gap in grain production efficiency among counties in Inner Mongolia, Hebei, Heilongjiang and Henan provinces, according to a distribution map of that efficiency.

Dynamic changes in carbonate chemistry in the microenvironment around single marine phytoplankton cells

Photosynthesis by marine diatoms plays a major role in the global carbon cycle, although the precise mechanisms of dissolved inorganic carbon (DIC) uptake remain unclear. A lack of direct measurements of carbonate chemistry at the cell surface has led to uncertainty over the underlying membrane transport processes and the role of external carbonic anhydrase (eCA). Here we identify rapid and substantial photosynthesis-driven increases in pH and [CO32−] primarily due to the activity of eCA at the cell surface of the large diatom Odontella sinensis using direct simultaneous microelectrode measurements of pH and CO32− along with modelling of cell surface inorganic carbonate chemistry. Our results show that eCA acts to maintain cell surface CO2 concentrations, making a major contribution to DIC supply in O. sinensis. Carbonate chemistry at the cell surface is therefore highly dynamic and strongly dependent on cell size, morphology and the carbonate chemistry of the bulk seawater.

Evaluation of forest CO2 fluxes from sonde measurements in three different climatological areas including Borneo, Malaysia, and Iriomote and Hokkaido, Japan

Evaluation of carbon dioxide (CO2) sinks in forest areas of East and Southeast Asia (especially tropical regions) is important for assessing CO2 budgets at the regional scale. To evaluate the CO2 flux of large forest areas, we collected vertical CO2 profiles over the forest using a CO2 sonde and measured surface CO2 concentrations around the forest using continuous CO2 measurement equipment. These observations were performed over a typical northern forest (Hokkaido) in Japan, a subtropical forest island (Iriomote Island) in Japan, and a tropical forest in Borneo Island. We detected the differences in CO2 vertical profiles between dawn and daytime, and at the upwind and downwind sites of the forests with the observational results from the CO2 sonde. We also clarified that CO2 concentrations during daytime at the downwind sites (affected by the forest) were systematically lower than those at the upwind sites (not affected by the forest). In contrast, CO2 concentrations during dawn at the downwind sites were larger than those at the upwind site. We estimated the CO2 fluxes (μmol m−2 s−1) at dawn and daytime of the forests from these observational results. The CO2 fluxes of Borneo’s forest were very large (16.5 and −37.7 at dawn and daytime, respectively), whereas the CO2 fluxes of the forests in Hokkaido and Iriomote were lower (3.9 to 11.8 at dawn and −11.8 to −15.0 at daytime). These evaluated values were consistent with fluxes measured by the eddy-covariance method in the same region. Thus, use of the CO2 sonde to collect observations of CO2 vertical profiles was considered to be an effective method to verify CO2 absorption and emission in large forest areas. This method can also be used to evaluate dynamic CO2 absorption and emission processes in tropical forests.

Assessment of soil carbon pool, carbon sequestration and soil CO2 flux in unreclaimed and reclaimed coal mine spoils

Surface coal mining inevitably deforests the land, reduces carbon (C) pool and generates different land covers. To re-establish the ecosystem C pool, post-mining lands are often afforested with fast-growing trees. A field study was conducted in the 5-year-old unreclaimed dump and reclaimed coal mine dump to assess the changes in soil CO2 flux and compared with the reference forest site. Changes in soil organic carbon (SOC) and total nitrogen stocks were estimated in post-mining land. Soil CO2 flux was measured using close dynamic chamber method, and the influence of environmental variables on soil CO2 flux was determined. Woody biomass C and SOC stocks of the reference forest site were threefold higher than that of 5-year-old reclaimed site. The mean soil CO2 flux was highest in 5-year-old reclaimed dump (2.37 μmol CO2 m−2 s−1) and lowest in unreclaimed dump (0.21 μmol CO2 m−2 s−1). Soil CO2 flux was highly influenced by environmental variables, where soil temperature positively influenced the soil CO2 flux, while soil moisture, relative humidity and surface CO2 concentration negatively influenced the soil CO2 flux. Change in soil CO2 flux under different land cover depends on plant and soil characteristics and environmental variables. The study concluded that assessment of soil CO2 flux in post-mining land is important to estimate the potential of afforestation to combat increased emission of soil CO2 at regional and global scale.

Multi-year application of WRF-CAM5 over East Asia-Part I: Comprehensive evaluation and formation regimes of O3 and PM2.5

Accurate simulations of air quality and climate require robust model parameterizations on regional and global scales. The Weather Research and Forecasting model with Chemistry version 3.4.1 has been coupled with physics packages from the Community Atmosphere Model version 5 (CAM5) (WRF-CAM5) to assess the robustness of the CAM5 physics package for regional modeling at higher grid resolutions than typical grid resolutions used in global modeling. In this two-part study, Part I describes the application and evaluation of WRF-CAM5 over East Asia at a horizontal resolution of 36-km for six years: 2001, 2005, 2006, 2008, 2010, and 2011. The simulations are evaluated comprehensively with a variety of datasets from surface networks, satellites, and aircraft. The results show that meteorology is relatively well simulated by WRF-CAM5. However, cloud variables are largely or moderately underpredicted, indicating uncertainties in the model treatments of dynamics, thermodynamics, and microphysics of clouds/ices as well as aerosol-cloud interactions. For chemical predictions, the tropospheric column abundances of CO, NO2, and O3 are well simulated, but those of SO2 and HCHO are moderately overpredicted, and the column HCHO/NO2 indicator is underpredicted. Large biases exist in the surface concentrations of CO, NOx, and PM10 due to uncertainties in the emissions as well as vertical mixing. The underpredictions of NO lead to insufficient O3 titration, thus O3 overpredictions. The model can generally reproduce the observed O3 and PM indicators. These indicators suggest to control NOx emissions throughout the year, and VOCs emissions in summer in big cities and in winter over North China Plain, North/South Korea, and Japan to reduce surface O3, and to control SO2, NH3, and NOx throughout the year to reduce inorganic surface PM.

Recent increase in surface fCO2 in the western subtropical North Pacific

We observed unusually high levels (> 440 μatm) of carbon dioxide fugacity (fCO2) in surface seawater in the western subtropical North Pacific, the area where Subtropical Mode Water is formed, during summer 2015. The NOAA Kuroshio Extension Observatory moored buoy located in this region also measured high CO2 values, up to 500 μatm during this period. These high sea surface fCO2 (fCO2SW) values are explained by much higher normalized total dissolved inorganic carbon and slightly higher normalized total alkalinity concentrations in this region compared to the equatorial Pacific. Moreover, these values are much higher than the climatological CO2 values, even considering increasing atmospheric CO2, indicating a recent large increase in sea surface CO2 concentrations. A large seasonal change in sea surface temperature contributed to higher surface fCO2SW in the summer of 2015.

Sphagnum farming in a eutrophic world: The importance of optimal nutrient stoichiometry

Large areas of peatlands have worldwide been drained to facilitate agriculture, which has adverse effects on the environment and the global climate. Agriculture on rewetted peatlands (paludiculture) provides a sustainable alternative to drainage-based agriculture. One form of paludiculture is the cultivation of Sphagnum moss, which can be used as a raw material for horticultural growing media. Under natural conditions, most Sphagnum mosses eligible for paludiculture typically predominate only in nutrient-poor wetland habitats. It is unknown, however, how the prevailing high nutrient levels in rewetted agricultural peatlands interfere with optimal Sphagnum production.We therefore studied the effect of enriched nutrient conditions remaining even after top soil removal and further caused by external supply of nutrient-rich irrigation water and (generally) high inputs of atmospheric nitrogen (N) to habitat biogeochemistry, biomass production and nutrient stoichiometry of introduced Sphagnum palustre and S. papillosum in a rewetted peatland, which was formerly in intensive agricultural use.Airborne N was responsible for the major supply of N. Phosphorus (P) and potassium (K) were mainly supplied by irrigation water. The prevailing high nutrient levels (P and K) are a result of nutrient-rich irrigation water from the surroundings. Peat porewater (10cm below peatmoss surface) CO2 concentrations were high, bicarbonate concentrations low, and the pH was around 4.2.Provided that moisture supply is sufficient and dominance of fast-growing, larger graminoids suppressed (in order to avoid outshading of Sphagnum mosses), strikingly very high biomass yields of 6.7 and 6.5tDWha−1yr−1 (S. palustre and S. papillosum [including S. fallax biomass], respectively) were obtained despite high N supply and biomass N concentrations. Despite high P and K supply and uptake, N:P and N:K ratios in the Sphagnum capitula were still low. Sphagnum mosses achieved high nutrient sequestration rates of 34kgN, 17kgK and 4kgPha−1yr−1 from May 2013 to May 2014, which shows that the site acted as an active nutrient sink. Nutrient management still needs further improvement to reduce the competitive advantage of fast growing peatmoss species (cf. S. fallax) at the expense of slower growing but preferred peatmosses as horticultural substrate (S. palustre and S. papillosum) to optimize the quality of biomass yields.In conclusion, Sphagnum farming is well able to thrive under high N input provided that there is a simultaneous high input of P and K from irrigation water, which facilitates high production rates. Due to the lack of suitable, nutrient poor sites, it seems to be useful to remove the topsoil (mainly P removal) prior to start growing Sphagnum mosses. In addition, bicarbonate concentrations have to stay sufficiently low to ensure a low pH, CO2 supply from the peat soil should be sufficiently high to prevent C limitation, and graminoids should be mown regularly.

Potential impacts of electric vehicles on air quality in Taiwan

The prospective impacts of electric vehicle (EV) penetration on the air quality in Taiwan were evaluated using an air quality model with the assumption of an ambitious replacement of current light-duty vehicles under different power generation scenarios. With full EV penetration (i.e., the replacement of all light-duty vehicles), CO, VOCs, NOx and PM2.5 emissions in Taiwan from a fleet of 20.6 million vehicles would be reduced by 1500, 165, 33.9 and 7.2Ggyr−1, respectively, while electric sector NOx and SO2 emissions would be increased by up to 20.3 and 12.9Ggyr−1, respectively, if the electricity to power EVs were provided by thermal power plants. The net impacts of these emission changes would be to reduce the annual mean surface concentrations of CO, VOCs, NOx and PM2.5 by about 260, 11.3, 3.3ppb and 2.1μgm−3, respectively, but to increase SO2 by 0.1ppb. Larger reductions tend to occur at time and place of higher ambient concentrations and during high pollution events. Greater benefits would clearly be attained if clean energy sources were fully encouraged. EV penetration would also reduce the mean peak-time surface O3 concentrations by up to 7ppb across Taiwan with the exception of the center of metropolitan Taipei where the concentration increased by <2ppb. Furthermore, full EV penetration would reduce annual days of O3 pollution episodes by ~40% and PM2.5 pollution episodes by 6–10%. Our findings offer important insights into the air quality impacts of EV and can provide useful information for potential mitigation actions.

Isotopic insights into methane production, oxidation, and emissions in Arctic polygon tundra.

Arctic wetlands are currently net sources of atmospheric CH4 . Due to their complex biogeochemical controls and high spatial and temporal variability, current net CH4 emissions and gross CH4 processes have been difficult to quantify, and their predicted responses to climate change remain uncertain. We investigated CH4 production, oxidation, and surface emissions in Arctic polygon tundra, across a wet-to-dry permafrost degradation gradient from low-centered (intact) to flat- and high-centered (degraded) polygons. From 3 microtopographic positions (polygon centers, rims, and troughs) along the permafrost degradation gradient, we measured surface CH4 and CO2 fluxes, concentrations and stable isotope compositions of CH4 and DIC at three depths in the soil, and soil moisture and temperature. More degraded sites had lower CH4 emissions, a different primary methanogenic pathway, and greater CH4 oxidation than did intact permafrost sites, to a greater degree than soil moisture or temperature could explain. Surface CH4 flux decreased from 64nmolm(-2) s(-1) in intact polygons to 7nmolm(-2) s(-1) in degraded polygons, and stable isotope signatures of CH4 and DIC showed that acetate cleavage dominated CH4 production in low-centered polygons, while CO2 reduction was the primary pathway in degraded polygons. We see evidence that differences in water flow and vegetation between intact and degraded polygons contributed to these observations. In contrast to many previous studies, these findings document a mechanism whereby permafrost degradation can lead to local decreases in tundra CH4 emissions.

A century of human‐driven changes in the carbon dioxide concentration of lakes

AbstractNow that evasion of carbon dioxide (CO2) from inland waters is accounted for in global carbon models, it is crucial to quantify how these fluxes have changed in the past and forecast how they may alter in the future in response to local and global change. Here we developed a sediment proxy for the concentration of summer surface dissolved CO2 concentration and used it to reconstruct changes over the past 150 years for three large lakes that have been affected by climate warming, changes in nutrient load, and detrital terrigenous supplies. Initially CO2 neutral to the atmosphere, all three lakes subsequently fluctuated between near equilibrium and supersaturation. Although catchment inputs have supplied CO2 to the lakes, internal processes and reallocation have ultimately regulated decadal changes in lake surface CO2 concentration. Nutrient concentration has been the dominant driver of CO2 variability for a century although the reproducible, nonmonotonic relationship of CO2 to nutrient concentration suggests an interplay between metabolic and chemical processes. Yet for two of these lakes, climatic control of CO2 concentrations has been important over the last 30 years, promoting higher surface CO2 concentrations, likely by decreasing hypolimnetic carbon storage. This new approach offers the unique opportunity to scale, a posteriori, the long‐term impact of human activities on lake CO2.

Carbon stable isotopes as indicators of the origin and evolution of CO2 and CH4 in urban solid waste disposal sites and nearby areas

Isotopic compositions of CH4 and CO2 surface and subsurface gases and groundwater from an urban solid waste disposal site from Gualeguaychu city (Argentina) were measured to detect origin, depth distribution, migration lateral, CH4 oxidation, and dissolution in groundwater. The highest CH4 concentrations (60–88 %) with δ13C-CH4 (between −60 and −45 ‰) and δ2H-CH4 (between −350 and −260 ‰) were attributed to CH4 originated by microbial sources, v. gr. acetate fermentation. The δ13C-CO2 related to this CH4 (between −15 and −5.9 ‰) were compatible with this process. Also, the increase of DIC associated to an increase in δ13C-DIC values (−12.4, −6.4, −5.8, −1.5, +0.1 and +4 ‰) indicated the transport of dissolved gases (from methanogenesis) in the groundwater flow system. High excess deuterium in 3 piezometers suggests that there were hydrogen isotope exchange between CH4 and water too. Evidences for CH4 oxidation were decrease in CH4 concentrations, shift in C and H isotope ratios of CH4 to more enriched in the remaining CH4 (in both, δ13C-CH4 >−50 ‰ and δ2H >−260 ‰) and depletion in 13C of the associated CO2 (<−20 ‰). Since surface CH4 and CO2 concentrations over the covering layer were very low, and the major CH4 concentrations were found between 60m and 90 cm depth, it is very probable USW has been compacted with low permeability materials (e.g., clay) avoiding large emissions to the atmosphere and creating horizontal barriers within the waste that enable lateral gas migration. Horizontally, it can be seen that these gases migrated outside the disposal site following the topography and that CH4 disappeared leading to anomalous concentrations of CO2 whose values are greater than those produced by normal soil respiration. The isotopic value (δ13C) of this CO2 was also different from that of normal soil respiration (~−25 ‰) and reflected effects that generated isotopic depletion by diffusion (~−25 to −32 ‰). The analysis of C isotopes as the main tracer, together H isotopes, has allowed the effective detection of the origin and those secondary processes.

Multi-species chemical data assimilation with the Danish Eulerian hemispheric model: system description and verification

Satellite retrievals of atmospheric composition provide a wealth of data on a global scale. These complement results from atmospheric chemistry-transport models (CTMs), and can be combined using data assimilation. We present two assimilation schemes coupled to the Danish Eulerian Hemispheric Model (DEHM), a three-dimensional, off-line CTM with full photochemistry: a variant on the ensemble Kalman filter and the three-dimensional variational scheme. The aim of this paper is to describe the two schemes and present an initial assessment of their impacts on model skill. Retrievals of multiple atmospheric trace gases are assimilated, namely: NO2 tropospheric column densities, CH4 total column densities, and partial column concentrations of O3, CO and CH4; these data are retrieved from four satellite sensors. Data for each species are assimilated independently of one another, and other species are only adjusted indirectly via the model’s chemistry and dynamics. Assimilation results are compared with measurements from surface monitoring stations and other satellite retrievals, and preliminary validation results are presented.Reference simulations (without assimilation) grossly underestimate surface CO concentrations, and both assimilation schemes eliminate this large and systematic model bias. The assimilation improves the spatial correlation of modelled CO with surface observations, and improves the spatial correlation between forecasts and retrievals for CO, NO2 and O3. Results for CH4 show a loss of skill due to a mismatch in model bias between two assimilated CH4 data-sets. Finally, we discuss differences in methodology and results between this paper and a recent study on multi-species chemical data assimilation. Joint optimisation of initial conditions and emission rates offers a promising direction for improving modelled boundary-layer concentrations.

Why does surface ozone peak before a typhoon landing in southeast China?

Abstract. A high O3 episode with the large increases in surface ozone by 21–42 ppbv and the nocturnal surface O3 levels exceeding 70 ppbv was observed in the region between Xiamen and Quanzhou over the southeastern coast of China during 12–14 June 2014, before the Typhoon Hagibis landing. Variations in the surface O3, NO2, CO and meteorology during the Typhoon Hagibis event clearly suggest a substantial impact of the peripheral downdrafts in the large-scale typhoon circulation on such an O3 episode excluding the contributions of photochemical production and the horizontal transport. The influence of vertical O3 transport from the upper troposphere and lower stratosphere (UTLS) region on high surface O3 levels is further confirmed by a negative correlation between surface O3 and CO concentrations as well as dry surface air observed during the O3 episode. This study provides observational evidence of typhoon-driven intrusion of O3 from the UTLS region to surface air, revealing a significant effect of such a process of stratosphere–troposphere exchange (STE) of O3 on tropospheric O3 and ambient air quality.

Spatial variation of near-surface CO2 concentration during spring in Shanghai

Urban area plays an important role in global carbon cycle, yet few efforts have been made to investigate CO2 concentration and its spatial heterogeneity in cities. Using Shanghai, the commercial and financial center of mainland China, as a case study, this paper explored the spatial pattern and determinants of near-surface urban CO2 concentration during spring. A total number of 173 sample points were collected covering the whole urban area, to examine the atmospheric CO2 concentration across various land use types (transportation, commercial, agricultural, recreational, institutional, residential and industrial land use) and urbanization gradients (heavy, moderately heavy, medium, moderately low, and low urbanization). CO2 concentrations were measured at a height of 2 m above the ground during 9:00–11:00 am in April and May 2014. The results indicated that CO2 concentration for the region was 409.4 ± 20.8 parts per million (ppm), showing significant spatial heterogeneity. The daytime ambient CO2 concentration varied across land use types (p < 0.05), with the highest and lowest value appeared in transportation area (420.5 ± 33.3 ppm) and agricultural land (398.9 ± 16.2 ppm). Across the urban gradients of Shanghai, a significant decrease of CO2 concentration was observed as the distance from urban core increased. With the influence of both high residential density and activities in production, the highest CO2 concentration occurred in moderate urbanization area (423.9 ± 29.3 ppm), rather than the high urbanization area (417.2 ± 17.5 ppm). Further analysis indicated that the percent of impervious surface cover (ISA) was an important indicator to describe near surface CO2 concentration with a positive correlation, and the percent of vegetation coverage (Veg) had lower explanatory power with a negative correlation. When buffer distance of spatial scale was 2000 m, atmospheric CO2 concentration showed the highest correlation with impervious surface and vegetation coverage.

Application of an Online-Coupled Regional Climate Model, WRF-CAM5, over East Asia for Examination of Ice Nucleation Schemes: Part II. Sensitivity to Heterogeneous Ice Nucleation Parameterizations and Dust Emissions

Aerosol particles can affect cloud microphysical properties by serving as ice nuclei (IN). Large uncertainties exist in the ice nucleation parameterizations (INPs) used in current climate models. In this Part II paper, to examine the sensitivity of the model predictions to different heterogeneous INPs, WRF-CAM5 simulation using the INP of Niemand et al. (N12) [1] is conducted over East Asia for two full years, 2006 and 2011, and compared with simulation using the INP of Meyers et al. (M92) [2], which is the original INP used in CAM5. M92 calculates the nucleated ice particle concentration as a function of ice supersaturation, while N12 represents the nucleated ice particle concentration as a function of temperature and the number concentrations and surface areas of dust particles. Compared to M92, the WRF-CAM5 simulation with N12 produces significantly higher nucleated ice crystal number concentrations (ICNCs) in the northern domain where dust sources are located, leading to significantly higher cloud ice number and mass concentrations and ice water path, but the opposite is true in the southern domain where temperatures and moistures play a more important role in ice formation. Overall, the simulation with N12 gives lower downward shortwave radiation but higher downward longwave radiation, cloud liquid water path, cloud droplet number concentrations, and cloud optical depth. The increase in cloud optical depth and the decrease in downward solar flux result in a stronger shortwave and longwave cloud forcing, and decreases temperature at 2-m and precipitation. Changes in temperature and radiation lower surface concentrations of OH, O3, SO42−, and PM2.5, but increase surface concentrations of CO, NO2, and SO2 over most of the domain. By acting as cloud condensation nuclei (CCN) and IN, dust particles have different impacts on cloud water and ice number concentrations, radiation, and temperature at 2-m and precipitation depending on whether the dominant role of dust is CCN or IN. These results indicate the importance of the heterogeneous ice nucleation treatments and dust emissions in accurately simulating regional climate and air quality.