Atmospheric Monitoring of Methane in Beijing Using a Mobile Observatory

Cities have multiple fugitive emission sources of methane (CH4) and policies adopted by China on replacing coal with natural gas in recent years can cause fine spatial heterogeneities at the range of kilometers within a city and also contribute to the CH4 inventory. In this study, a mobile observatory was used to monitor the real-time CH4 concentrations at fine spatial and temporal resolutions in Beijing, the most important pilot city of energy transition. Results showed that: several point sources, such as a liquefied natural gas (LNG) power plant which has not been included in the Chinese national greenhouse gas inventory yet, can be identified; the ratio “fingerprints” (CH4:CO2) for an LNG carrier, LNG filling station, and LNG power plant show a shape of “L”; for city observations, the distribution of CH4 concentration, in the range of 1940–2370 ppbv, had small variations while that in the rural area had a much higher concentration gradient; significant correlations between CO2 and CH4 concentrations were found in the rural area but in the urban area there were no such significant correlations; a shape of “L” of CH4:CO2 ratios is obtained in the urban area in wintertime and it is assigned to fugitive emissions from LNG sources. This mobile measurement methodology is capable of monitoring point and non-point CH4 sources in Beijing and the observation results could improve the CH4 inventory and inform relevant policy-making on emission reduction in China.

Monitoring variation in greenhouse gases concentration in urban environment of Delhi

Cities across the globe are considered as major anthropogenic sources of greenhouse gases (GHG), yet very few efforts has been made to monitor ambient concentration of GHG in cities, especially in a developing country like India. Here, variations in the ambient concentrations of carbon dioxide (CO(2)) and methane (CH(4)) in residential, commercial, and industrial areas of Delhi are determined from fortnightly daytime observations from July, 2008 to March, 2009. Results indicate that the average daytime ambient concentration of CO(2) varied from 495 to 554 ppm in authorized residential areas, 503 to 621 ppm in the slums or jhuggies in the unauthorized residential areas, 489 to 582 ppm in commercial areas, and 512 to 568 ppm in industrial areas with an average of 541 ± 27 ppm. CH(4) concentration varied from 652 to 5,356 ppbv in authorized residential areas, 500 to 15,220 ppbv in the unauthorized residential areas, 921 to 11,000 ppbv in the commercial areas, and 250 to 2,550 ppbv in the industrial areas with an average of 3,226 ± 1,090 ppbv. A low mid-afternoon CO(2) concentration was observed at most of the sites, primarily due to strong biospheric photosynthesis coupled with strong vertical mixing.

Monitoring of environmental parameters for CO2 sequestration: a case study of Nagpur City, India

Carbon dioxide concentration is an index of total amount of combustion and natural ventilation in an urban environment and therefore required more careful attention for assessment of CO(2) level in air environment. An attempt was made to monitor CO(2) levels in ambient air of Nagpur city at industrial, commercial and residential sites. In addition to this a remote sensing studies and biotic survey for floral biodiversity were carried out to study the green cover at respective sampling locations. The observations showed that the largest amount of CO(2) occurred at night due to absence of photosynthesis and lowest concentration of CO(2) was observed in the afternoon due to photosynthesis at its maximum level. The most pollution tolerant species found in Nagpur city are having higher Air Pollution Tolerance Index (APTI) value, which acts as a natural sink for CO(2) sequestration. In case of commercial site the CO(2) level is highest (366 ppm) because of lowest vegetation and vehicular pollution. The generation of database of CO(2) concentration and floral biodiversity along with percentage of green cover helps to formulate the strategy for prevention of global worming phenomenon.

Carbon-isotopic composition of soil-respired carbon dioxide in static closed chambers at equilibrium

The carbon-isotopic composition (delta13C) of soil-respired CO2 has been employed to evaluate soil carbon-cycling processes and the contribution of soil CO2 emissions to canopy and tropospheric air. These evaluations can be successful only when accurate isotope values of soil-respired CO2 are available. Here, we tested the robustness of delta13C values of soil-respired CO2 obtained after long incubations in static closed chambers that were initially flushed with soil air. The rationale of this approach is that the equilibrium carbon-isotope values of chamber-headspace CO2 are theoretically equal to those of CO2 produced within the soil. Static closed chambers were installed in replicated grass monocultures, and measurements of headspace CO2 concentrations and delta13C values were performed at regular time intervals for 24 h in July 2005. The results revealed no significant effects of grass species on headspace CO2 concentrations or delta13C values (repeated measures analysis of variance (ANOVA), P>0.1). As predicted by theory, isotope values asymptotically approached equilibrium conditions, which in our experimental setting occurred after 10 h. This good match between model predictions and our results suggests that an accurate determination of delta13C values of CO2 produced within soils is obtained through the isotopic measurement of chamber-headspace CO2 once equilibrium conditions have been reached with the underlying soils. An additional advantage of this approach is that only one sample per chamber is required, which, combined with the low uncertainties of these measurements, facilitates the investigation of the spatial (landscape) variability of soil-respired CO2.

Long series relationships between global interannual CO2 increment and climate: evidence for stability and change in role of the tropical and boreal-temperate zones

Interannual variability in global CO2 increment (averaged from the Mauna Loa and South Pole Stations) shows certain strong spatial relationships to both tropical and temperate temperatures. There is a fairly strong positive year-round correlation between tropical mean annual temperatures (leading by 4 months) and annual CO2 throughout the time series since 1960, agreeing with the generally held view that the tropics play a major role in determining inter-annual variability in CO2 increment, with a major CO2 pulse following a warm year in the tropics. This 'almost no lag' climatic response is very strong during winter and relatively stable in time. However, the correlation with tropical temperature appears to have weakened in the first years of the 1990s in correspondence of the Pinatubo eruption and the positive phase of the AO/NAO. A secondary concurrent temperature signal is linked to summer variations of north temperate belt. Northern summer temperatures in the region 30-60 degrees N-and especially in the land area corresponding to the central east USA-have become relatively more closely correlated with CO2 increment. This trend has become increasingly stronger in recent years, suggesting an increasing role for growing season processes in the northern midlatitudes in affecting global CO2 increment. Once non-lagged annual tropical temperature variations are accounted for, terrestrial ecosystems, especially the temperate-boreal biomes, also show a coherent large scale lagged response. This involves an inverse response to annual temperature of preceding years centered at around 2 years before. This lagged response is most likely linked to internal biogeochemical cycles, in particular N cycling. During the study period north boreal ecosystems show a strengthening of the lagged correlation with temperature in recent years, while the lagged correlation with areas of tropical ecosystems has weakened. Residuals from a multiple correlations based on these climatic signals are directly correlated with SO, confirming an additional important role of upwelling in interannual variability of CO2 increment. Cooler summers following the Pinatubo eruption and the possible influence of the North Atlantic Oscillation (NAO/AO) are discussed as factors responsible for the shift in the relative importance of different regions over time during the series of data.

Local-scale fluxes of carbon dioxide in urban environments: methodological challenges and results from Chicago

Much attention is being directed to the measurement and modeling of surface-atmosphere exchanges of CO2 for different surface types. However, as yet, few measurements have been conducted in cities, even though these environments are widely acknowledged to be major sources of anthropogenic CO2. This paper highlights some of the challenges facing micrometeorologists attempting to use eddy covariance techniques to directly monitor CO2 fluxes in urban environments, focusing on the inherent variability within and between urban areas, and the importance of scale and the appropriate height of measurements. Results from a very short-term study of CO2 fluxes, undertaken in Chicago, Illinois in the summer of 1995, are presented. Mid-afternoon minimum CO2 concentrations and negative fluxes are attributed to the strength of biospheric photosynthesis and strong mixing of local anthropogenic sources in a deep mixed layer. Poor night-time atmospheric mixing, lower mixed layer depths, biospheric respiration, and continued missions from mobile and fixed anthropogenic sources, account for the night-time maxima in CO2 concentrations. The need for more, longer-term, continuous eddy covariance measurements is stressed.