Importance of this paper: Methane emission from sedimentary layers of water basins occurs through molecular diffusion, bubbles and plants. The values of these fluxes are not independent. They can be estimated from a change in the concentrations of methane and nitrogen in the upper parts of a sedimentary layer. In this paper, diffusion equations are used to derive differential equations whose solution describes a change in the concentrations of gases in the sedimentary layer with depth. This allows one to estimate gas fluxes into the atmosphere.
The effect of green manure amendment, flooding treatment and crop season on methane emission from paddy fields in Taiwan was investigated from August 1994 to July 1996. Sesbania amendment stimulated methane emission and the effect was more significant at the early growth stage of rice. Methane emission was higher in continuous flooding treatment than that in intermittent irrigation. Both redox potential and methane emission showed significant differences between these two irrigation systems. Methane concentration increased sharply with the depth of soil in the intermittent irrigation system due to oxidation; whereas it increased moderately in the continuous flooding treatment. The seasonal methane flux in the first crop season with chemical fertilizer was between 2.73 and 5.23 g m−2; while the value was between 10.54 and 10.56 g m−2 in the second crop season. In the case of Sesbania amendment in the second crop season, the seasonal methane flux in the first crop season was 6.35 g m−2; while the value was between 14.43 and 30.12 g m−2 in the second crop season. Total methane emission in the second crop season was about two to five-fold higher than that in the first crop season.
Importance of this paper: Ammonia and ammonium (NHx) are important atmospheric components. Interest on the role of ammonia as an air pollutant has grown because of its importance both to atmospheric chemistry and because of the ecological consequences of its deposition to sensitive ecosystems. A substantial part of the acid in the atmosphere is neutralized by ammonia. As a result ammonium is a major component in aerosols and in precipitation. Oxidation of ammonium in the soil may lead to acidification. Ammonia is mainly emitted from animal manure, and application of fertilizers may lead to ammonia emissions. Increased depositions of ammonia may result in plant community changes.
Importance of this paper: In view of its impact on tropospheric chemistry and associated climate change, methane has assumed importance in recent years, especially because of its increasing ambient concentration. Rice paddy has been identified as one of the important source of anthropogenic methane. Both soil type and water regime play important roles in the process of methanogenesis and methane emission from rice soils. In view of wide spatial and seasonal variability and the importance of moisture on the process of methane emission, it is pertinent to evaluate the role of soil type and moisture interaction on methane efflux from soils planted to rice. In the present study, methane flux from two soils planted to rice was monitored in a greenhouse under non-flooded and flooded conditions.
Importance of this paper: Methane is present in the atmosphere in trace quantities but it is among the atmospheric greenhouse gases that trap radiation energy and has global warming 30 times that of CO2. The strengths of various sources of methane have been reasonably estimated but the sink estimation has been almost negligible due to inadequate availability of required data. For atmospheric methane, soil is an important sink besides others like reaction with OH and stratospheric removal. In this paper, an attempt has been made for the first time to make preliminary estimation of uptake by Indian soils under different eco-systems as a case study.
Context abstract: Methane is an important greenhouse gas. Livestock production constitutes a large part of total UK methane emission. By comparing livestock derived methane production with three theoretical sinks, the possibility of balancing methane production with direct consumption is assessed.
Importance of this Paper: This paper presents simultaneous observations of biogenic volatile organic compounds and particulate organic carbon (POC) in a eucalyptus forest and upwind locations. Thorough examination of the results enables the evaluation of the contribution of biogenic carbon to the observed organic particles relative to that of anthropogenic origin.
Importance of this Paper: Nitrate radicals (NO3) were discovered in the atmosphere in the late 1970s where they were formed by oxidation of NO2 by ozone. Since then NO3 has been identified as a strongly oxidizing agent, which plays an important role in the removal of many (in particular biogenic) hydrocarbons, and thus in the self-cleaning of the atmosphere. In contrast to most other free radicals (like e.g. the OH radical) NO3 is not directly formed by photochemical reactions, in fact NO3 is rapidly destroyed by sunlight, thus its abundance is highest at night. Since NO3 reactions lead to the conversion of NOx to HNO3 or nitrate, NO3 also is an important intermediate in the removal of NOx from the atmosphere.
Vertical profiles of carbonyl sulfide (COS) have been obtained in a eucalyptus forest in Portugal within the first 20 m above ground. Significantly lower mixing ratios were observed below the canopy level than above, indicating a net absorption of COS from the eucalyptus trees. The ratio between mean COS concentrations below and above the canopy was 0.86 in mid-afternoon, whereas in the morning and at midnight this ratio increased up to 0.97. COS mixing ratios were by more than 100 pptv higher above the canopy than below it in mid-afternoon, whereas in the morning and at midnight the difference never exceeded 25 pptv. At all levels COS presented a clear diurnal cycle with highest values around mid-afternoon. Experiments conducted in parallel with the enclosure chamber technique confirm the COS absorption from the eucalyptus trees. COS uptake reached its highest values in mid-afternoon, when photosynthetic active radiation (PAR) was maximum.
The production rates of a range of low molecular weight halogenated organics have been determined in cultures of five temperate species of macroalgae collected from the north coast of Norfolk, England. Compounds studied included CH3Br, the chlorinated organics CH3Cl, CH2Cl2 and CHCl3, and the iodinated organics CH3I, C2H5I, and CH2ClI. Measurements of a wider range of halocarbon concentrations in an isolated rockpool and in air over the seaweed bed were also conducted to evaluate the local impact of the seaweeds on halocarbon concentrations in the natural environment. Estimates for the global emissions of some of the key halogenated compounds from macroalgae have been derived. In general macrophytes appear not to be globally significant producers of the particular halocarbons studied. In coastal regions, however, the impact on local atmospheric composition and chemistry could be greater.
Gaseous methane (CH4) emissions were determined during the winter and summer from `farrow-to-finish' (FF) swine production houses and during the summer from a `farrow-to-wean' (FW) house in 1998 in the coastal plains of North Carolina. The houses were instrumented with sensors to determine cycling of the individual forced-ventilation fans. Laser spectrometry was used to measure CH4 concentration differences between the intake and exhaust points of the houses. Differences in CH4 concentrations were combined with fan operation data to calculate CH4 fluxes from the houses. During the cold winter measurement period, CH4 fluxes averaged 6.9 g CH4animal−1d−1 in the FF house. During summer measurement periods, CH4 fluxes were much greater and averaged 33 and 46 g CH4animal−1d−1 from the FF and FW houses, respectively. The much larger emissions during the summer than winter, indicate that CH4 house emissions were primarily from fresh feces and the underground storage/wash pits containing lagoon effluent; and not directly from the animals since temperature would have little affect on direct animal emission. Emission factors based on animal units (au) of 454 kg animal−1 were much greater at the FW farm with a pull-plug waste management system (7–8 day wash cycle) than at the FF farm with a periodic flush system (8 h wash cycle).
The impact of the oxidation of natural non-methane hydrocarbon, particularly of isoprene, on the free radical formation and on ozone budgets has been evaluated on the basis of the results of the FIELDVOC'94 campaign. Four reduced chemical mechanisms for hydrocarbon oxidation and a detailed chemical scheme for C1–C5 hydrocarbon oxidation incorporated into a box model suitable for the integration of stiff chemical reactions have been used for this study. The observed peroxy radical concentrations are well simulated by the models. Hydroperoxy radicals contribute by about 40–60% to the daytime peak of peroxy radicals. Terpenes and isoprene chemistry could account for about 10% and 45% of the observed levels of daytime peroxy radical concentrations. Ozone reactions contribute up to 50% to the organic peroxy radicals produced at night by isoprene oxidation. Isoprene chemistry reduces by a factor of two to three the computed radical concentrations and contributes by about 50–100% to the net ozone daytime photochemical production in this forested area.
Major ion and trace metal concentrations were determined in aerosols and cloud water at a site in the Himalayan Mountains of Northern Pakistan. In spite of the fact that the site is well removed from significant urban/industrial pollution sources the SO2−4 concentrations in some of the samples were as high as those observed in North America. Concentrations of Se, Tl, Pb, Cl, Cd, Sb, Zn, and As in aerosols were highly enriched relative to average crustal abundances indicating significant anthropogenic contributions. Cloud water concentrations of major ions and trace elements are reported for 18 samples from six different clouds. The pH varied between 5.3 and 6.8 in spite of the fact that the SO2−4 concentration approached 300 μmol in some samples, values often observed in the northeastern US. Selenium was used as a tracer to determine in-cloud production of SO2−4 in these clouds and in three of the six clouds 40–60% of the observed SO2−4 came from in-cloud production.
An important focus of climate-change research is the understanding of the role of ecosystems in shaping climate. Central to this aim is the identification of any feedbacks by which ecosystems may moderate anthropogenic forcing of climate. One possible ecosystem feedback involves the marine food-web and the biogenic sulfur compound dimethylsulfide (DMS). DMS is produced by algae containing the precursor compound dimethylsulfoniopropionate (DMSP), and once ventilated to the atmosphere can be transformed to sulfate aerosols and global climate. It was hypothesized that an increase in biogenically produced sulfate aerosols leading to formation of more cloud condensation nuclei (CCN), and brighter clouds, could stabilize the climate against perturbations due to greenhouse warming. Although a large database of DMS seawater measurements exist, attempts to statistically correlate DMS concentrations with other biological parameters, such as chlorophyll a or nutrients, have failed. This underscores the complex and dynamic nature of the DMS cycle, and means that simple regression-type predictive models are unlikely to be useful, except at local scales. Regional-scale simulations of the DMS cycle have involved multi-parameter, deterministic formulations based on ecological food-web approaches but with the added challenge of properly simulating the behavior of coupled sulfur and nitrogen (or carbon) cycles. Here we review the current DMS modeling approaches, outline the parameterization of key processes, and identify areas where our knowledge is poor and improvements should be made. Model skill can only be assessed against detailed regional and global data sets, however data have not always been collected in a form suitable for model parameter estimation or model calibration/validation. DMS time series, which are essential for calibration of seasonal or multi-annual simulations, are rare. We discuss the minimum requirements for a successful future integration of observational and theoretical efforts.
Gradients of CO and CO2, taken between 12:00 and 15:00 local time, from the boundary layer over the tropical rainforest in Surinam were determined as 29 pmol/mol km−1 and −8.9 nmol/mol km−1, respectively, with a distance of south from the coast. For one CO2 molecule fixed in tropical forests 0.33% CO was produced. From an extrapolation of the CO gradient to the global scale we deduce that approximately 19% of C emitted as isoprene from tropical forests is converted to C in CO. From an extrapolation of the CO2 gradient we estimate that approximately 1.2% of the global atmospheric CO2 is converted each year into tropical seasonal and rainforests.CO production from isoprene was calculated using an explicit gas-phase photochemical model but was found to be insufficient to account for the gradients measured. Diurnal variation in CO was controlled by a complex interplay between advection, chemical formation from natural NMHCs, direct soil emissions, removal by HO, and possible night-time uptake by soil. Diurnal variations of CO2 in the boundary layer were controlled by vegetation.Over the 12.5 km altitude range of the aircraft, a high degree of variability was observed in CO, CO2 and northerly wind components. Two biomass burning events were identified and the ratio of delta CO and delta CO2 was determined in each case with a two-sided linear regression. A ratio of 12.1% was found in plumes from smouldering cooking or clearing fires at low-altitude. A ratio of 5.9% was found for a plume encountered between 10–12 km. The lower ratio of delta CO and delta CO2 indicates hotter, more complete, flame burning than the cooking or clearing fires. Emissions from savanna fires in the Brazil, Colombia and Venezuela regions coupled with deep convection and long-range advection are proposed to explain the observations.
The dominant processes affecting the concentration of tropospheric methane on interannual timescales are the biospheric and anthropogenic sources and changes in the abundance of the hydroxyl radical caused by the changes in the UV flux which result from changes in stratospheric ozone abundance. We have carried out an empirical study of the sensitivity of the methane to fluctuations in ozone column abundance. This analysis was carried out using monthly mean surface methane concentrations measured by the National Oceanic and Atmospheric Administration – Climate Monitoring and Diagnostics Laboratory (NOAA-CMDL) Global Cooperative Air Sampling Network from 1983 to 1998 and ozone column abundances obtained by the Total Ozone Mapping Spectrometer (TOMS) and the EP TOMS instruments over the same time period. We focused on interannual variability with periods between 15 and 60 months, in which interval the dominant ozone fluctuation is the quasi-biennial oscillation (QBO), with a period of approximately 29 months. In order to isolate the response of methane to ozone from the effects of variability in the sources and transport of methane, we restricted our analysis to data at mid-latitudes in the southern hemisphere. A statistical study shows that the sensitivity factor α≡−d(ln[CH4])/d(ln[O3])=−0.038±0.009. The response of CH4 lags approximately 6 months behind the forcing by O3. A simple model was used to interpret the empirical results. Our results confirm that any mechanism that affects stratospheric ozone impacts the oxidizing potential of the troposphere. CH4 fluctuations provide a quantitative measure of this important effect linking the upper and the lower atmosphere.
In Japan, five types of vehicles, light-duty gasoline [(LDG); 550 cc<engine displacement (ED)], super-light-duty gasoline [(SLD); ED<550 cc], liquid petroleum-fueled [(LPG); 550 cc<ED<3000 cc], light-duty diesel [(LDD); 550 cc<ED<5000 cc] and heavy-duty diesel [(HDD); 5000 cc<ED] cars have been used widely to give the complex influences on the hydrocarbon components at roadsides and in city areas, which have not been explained sufficiently. In this study, we investigated the ambient 16 hydrocarbon components at two roadsides in commercial and industrial areas of Osaka City along with the traffic densities of five types of vehicles to propose the significant effects of emissions from SLD and LPG cars besides that of LDG car through a comparison of the ambient [ethylene]/[acetylene] and [i-, n-pentanes]/[i-, n-butanes] ratios with those of the source profiles published in Japan.
The aim of the EU FIELDVOC'94 project (field study on the tropospheric degradation mechanisms of biogenic VOCs, isoprene and dimethylsulfide) was to understand the contribution of the isoprene chemistry to the budget of ozone and the formation of peroxy radicals (RO2) under various conditions, particularly high and low nitrogen oxides concentrations (NOx). An additional objective was to evaluate the involvement of nitrate radicals (NO3) in the production of RO2 during night-time. An experiment was undertaken in June–July 1994, at a forest site in central Portugal. During this campaign most of the compounds involved in the ozone/isoprene chemistry were measured, i.e., nitrogen oxides, carbon monoxide, degradation and secondary products (aldehydes, ketones, organic acids and peroxides), as well as free radicals (RO2 and NO3). Several intensive measurement periods were carried out under different conditions of high and low photochemical activity. Isoprene was the most abundant hydrocarbon measured at the site, with mixing ratios as high as 10–12 ppbv during periods of high photochemical activity and elevated temperatures. Terpenes were also produced in the ppbv level with maximum concentrations observed at night. Ozone exhibited a diurnal variability, with maximum levels in the afternoon of 80–100 ppbv attributed to the interaction of polluted air masses and the isoprene chemistry. NO3 radicals never exceeded a maximum of 6 pptv. RO2 radicals displayed a diurnal maximum of 200–250 pptv and in some case reached night-time levels of 10–20 pptv. Radicals and ozone budgets deduced from photostationary models or chemical box models showed that hydroxyl radical (OH) initiated isoprene chemistry contributed to about 45% of the observed NO3 levels during daytime and that ozone initiated chemistry accounted for approximately half of the RO2 observed. The chemistry of isoprene strongly enhanced the ozone net production and reduced by a factor 2–3 the OH concentration.
Context Abstract: Tropical deciduous fires from shifting cultivation process in India are characterized by the highly differential nature of fire behavior due to fragmented burning patterns. Our study from ground-based experiments from biomass burning of tropical deciduous forest fires suggests smoldering combustion as the dominating process during biomass burning which leads to evolution of more incompletely oxidized products such as Methane when compared to other ecosystems such as Savannas. In the study, we report emission ratios and emission factors for methane from biomass burning of tropical deciduous forests. As tropical deciduous forests in India cover more than 50% of overall forests, the emission factors obtained in the present study can be used widely for methane emission estimation from forest biomass burning studies in other parts of India and in modeling studies of Methane from forest biomass burning in India.Main Abstract: Biomass burning is an important source of trace gas emissions to the atmosphere. Methane emitted from the biomass burning contributes to the atmospheric greenhouse effect and is sufficiently long-lived to enter the stratosphere and take part in the stratospheric ozone cycles. In India, though CH4 emissions from the different sources such as rice paddy fields and domestic animals have been well studied, there are relatively no field-based studies with respect to CH4 emissions from biomass burning. In the present study, we report for the first time, the CH4 emissions from biomass burning of tropical deciduous forests cleared for shifting cultivation purposes. Trace gas emissions from the biomass burning plumes have been collected through grab sampling in canisters as well as from online measurements through instruments. Site characteristics with respect to species composition, amount of biomass burnt and relative amounts of combustion, viz., flaming, mixed and smoldering have been determined. Modified combustion efficiency has been used to differentiate relative amounts of combustion. Emission ratios were calculated with respect to CO2 and emission factors based on the amount of biomass consumed. Results of the study with respect to biomass estimations prior to burning suggested values of 12–14 t ha−1 at the first site and 13.5–15.3 t ha−1 at the second site. The mean modified combustion efficiencies during flaming, mixed and smoldering combustion phases for the first site were found to be 95.7%, 91.1% and 74.4% and 95.31%, 90.63% and 72.89%, respectively, for the second site. The average biomass consumed during the fire ranged from 4.7 t ha−1 (site 1) to 3.4 t ha−1 (site 2), indicating low amount of biomass burnt during the first phase of burning in shifting cultivation areas. Results suggested the CH4 emission ratios of 1.29% at the first site and 1.59% at the second site. The CH4 emission ratios obtained in the present study are closer to the most accepted estimates of 1.2±0.5% obtained for tropical forests elsewhere. Using the emission ratios obtained in the study and estimating the amount of methane emissions from biomass burning suggests that nearly 0.99 Tg of methane is emitted annually from shifting cultivation process in India. Also, in the study, a detailed comparison of emission ratios and emission factors of CH4 has been made.
