Carbon Monoxide Budget Research Articles

Stable isotopic compositions and fractionations of carbon monoxide at coastal and open ocean stations in the Pacific

Included in this report are the results of the first isotopic studies of seawater‐dissolved carbon monoxide (CO). Large variations in both carbon and oxygen isotopic compositions (δ13C: −44.7 ∼ −21.1‰PDB, and δ18O: +8.7 ∼ +32.9‰SMOW) were observed in seawater‐dissolved CO due to the combination of isotopically light CO production in seawater and the enrichment of heavy isotopes during the microbial consumption of CO. Compared with the total δ13C value of dissolved organic matter (DOM), the isotopic compositions of the photochemically produced CO in seawater are depleted in 13C by more than 20‰, probably due to large fractionation processes during the photochemical production of CO from DOM. In addition, the isotopic fractionation factors resulting from the microbial oxidation of CO in seawater were estimated to be 1.005 ± 0.002 and 1.006 ± 0.002 for carbon (αc) and oxygen (αo) based on the incubation experiments. By calculating the weighted mean of the isotopic composition of CO according to the CO concentration observed in surface seawater, the mean δ13C and δ18O for CO emitted from the oceans were estimated to be −40‰ PDB and +15‰ SMOW, respectively. Oceanic CO is a unique source of 13C and 18O‐depleted CO relative to that of fossil fuel combustion and biomass burning, which will help us create a better isotopic mass balance for both global and local CO budget.

Concordant estimates of oceanic carbon monoxide source and sink processes in the Pacific yield a balanced global “blue‐water” CO budget

Studies to characterize sources and sinks of carbon monoxide (CO) in the mixed layer were carried out at sites covering large regions of the north and south Pacific. Apparent quantum yield spectra for the photochemical production of CO from colored dissolved organic matter were measured, as were first‐order net microbial CO consumption rate constants. Contrary to initial expectations, neither photoproduction nor biooxidation parameters exhibited strong regional variations, except that in the Southern Ocean CO biooxidation rate coefficients were very low. Global “blue‐water” CO flux terms derived from the data (in Tg carbon from CO per year, CO‐C a−1) are: photochemical source, 50 (estimated range, 30–70), microbial sink, 32 (estimated range, 10–60) and total CO sink (microbial plus gas exchange), 38 (estimated range, 13–60). Considering uncertainties and extrapolation biases, these independently estimated source and sink terms are thus in, or close to, balance at ∼40 (range of overlap, 30–60) Tg CO‐C a−1. The simplest interpretation of this balance is that no major net sources or sinks (i.e., light‐independent production, photoproduction at >450 nm) remain undiscovered, though considerable uncertainty in actual process rates remains. These CO fluxes are, however, very much smaller than some recently estimated values. The origins and implications of these discrepancies are discussed, and the coastal budget term is approximated.

Atmospheric emission and cycling of carbon monoxide in the Scheldt estuary

Axial profiles of dissolved carbon monoxide(CO) from four surveys of the Scheldt estuaryconfirmed that the estuary is a source ofatmospheric CO, with an emission range of 4–404nmol m−2 h−2. Surface water COconcentration and atmospheric emission werespatially variable, with an order of magnitudedifference between the upper and lower estuaryin spring, and seasonally variable with highestlevels in spring and lowest in winter. AnnualCO emission was estimated to be 700 (396–1032)× 103 mol, equivalent to 0.02–0.05% ofdissolved organic carbon (DOC) input to theestuary. CO photoproduction rates were an orderof magnitude greater in the upper estuary inspring and correlated with DOC concentration.Total CO production from DOC photodegradationwas estimated to be 8.5–18 × 103 mol COd−1, equivalent to 0.21–0.44% of riverineDOC input in spring. The deficit betweenproduction and emission suggests that microbialCO oxidation accounts for 68% of photoproducedCO, with highest oxidation rates at lowsalinities. The results indicate that suspendedparticulate material indirectly influencesestuarine CO distribution and emission.Assuming that the Scheldt is representative, estuaries do notcontribute significantly to the oceanic or global CO budgets.

Isoprene and monoterpene emission from the coniferous species Abies Borisii-regis—implications for regional air chemistry in Greece

The emission of isoprene has been studied from a forest of Abies Borisii-regis, a Mediterranean fir species previously thought to emit only monoterpenes. Emission studies from two independent enclosure experiments indicated a standardised isoprene emission rate of (18.4±3.8) μg g dry-weight −1 h −1, similar in magnitude to species such as eucalyptus and oak which are considered to be strong isoprene emitters. Isoprene emission depended strongly on both leaf temperature (2°C–34°C) and photosynthetically active radiation (PAR) below 250 μmol m −2 s −1, becoming saturated with respect to PAR above this value. The annual isoprene emission rate was estimated to be (132±29) kT yr −1 for those trees growing within Greece, comparable to current estimates of the total isoprene budget of Greece as a whole, and contributing significantly to regional ozone and carbon monoxide budgets. Monoterpene emission exhibited exponential temperature dependence, with 1,8-cineole, α-pinene, β-pinene and limonene forming the primary emissions. A standardised total monoterpene emission rate of (2.7±1.1) μg g dry-weight −1 h −1 was calculated, corresponding to an annual monoterpene emission rate of (24±12) kT yr −1. Research was conducted as part of the AEROBIC’97 (AEROsol formation from BIogenic organic Carbon) series of field campaigns.

Global distribution of carbon monoxide

This study explores the evolution and distribution of carbon monoxide (CO) using the National Oceanic and Atmospheric Administration (NOAA) Geophysical Fluid Dynamics Laboratory three‐dimensional global chemical transport model (GFDL GCTM). The work aims to gain an improved understanding of the global carbon monoxide budget, specifically focusing on the contribution of each of the four source terms to the seasonal variability of CO. The sum of all CO sources in the model is 2.5 Pg CO/yr (1 Pg = 103Tg), including fossil fuel use (300 Tg CO/yr), biomass burning (748 Tg CO/yr), oxidation of biogenic hydrocarbons (683 Tg CO/yr), and methane oxidation (760 Tg CO/yr). The main sink for CO is destruction by the hydroxyl radical, and we assume a hydroxyl distribution based on three‐dimensional monthly varying fields given bySpivakovsky et al. [1990], but we increase this field by 15% uniformly to agree with a methyl chloroform lifetime of 4.8 years [Prinn et al, 1995]. Our simulation produces a carbon monoxide field that agrees well with available measurements from the NOAA/Climate Monitoring and Diagnostics Laboratory global cooperative flask sampling network and from the Jungfraujoch observing station of the Swiss Federal Laboratories for Materials Testing and Research (EMPA) (93% of seasonal‐average data points agree within ±25%) and flight data from measurement campaigns of the NASA Global Tropospheric Experiment (79% of regional‐average data points agree within ±25%). For all 34 ground‐based measurement sites we have calculated the percentage contribution of each CO source term to the total model‐simulated distribution and examined how these contributions vary seasonally due to transport, changes in OH concentration, and seasonality of emission sources. CO from all four sources contributes to the total magnitude of CO in all regions. Seasonality, however, is usually governed by the transport and destruction by OH of CO emitted by fossil fuel and/or biomass burning. The sensitivity to the hydroxyl field varies spatially, with a 30% increase in OH yielding decreases in CO ranging from 4–23%, with lower sensitivities near emission regions where advection acts as a strong local sink. The lifetime of CO varies from 10 days over summer continental regions to well over a year at the winter poles, where we define lifetime as the turnover time in the troposphere due to reaction with OH.

Plant Production and Emission of Volatile Organic Compounds

\AI ways in which plant proV cesses influence the atmosphere, most biologists first think of photosynthetic oxygen production and carbon dioxide uptake. Given a few more minutes, many will also point out that plant transpiration of water plays a role in the chemistry of the troposphere (the lower 10 km of the atmosphere). Few, however, are aware that plant processes play key roles in ozone production, methane oxidation, and the global carbon monoxide budget. Several biologists and atmospheric chemists have recognized the effects of plants on the atmosphere (Rasmussen 1972, Tyson et al. 1974, Went 1960), but only recently has research into chemical emissions from plants advanced beyond a curiosity of interest to only a handful of environmental scientists. The topic of plant chemical emissions and their role in

Atmospheric carbon monoxide budget of the southern hemisphere: Implications of 13C/12C measurements

A large seasonal cycle has been observed in the 13C/12C isotopic ratio of CO in clean air in the extratropical southern hemisphere. This ratio is determined by the mixture of CO from isotopically distinct sources and is strongly influenced by the relative contributions of surface sources and the oxidation of CH4. We use a zonally averaged atmospheric model to relate atmospheric CO mixing ratios and 13C/12C isotopic ratios to the magnitude and distribution of CO sources and to explain the average seasonal cycles observed. The average 13C/12C ratio of CO emitted by surface sources in the southern hemisphere is larger than in the northern hemisphere and the southward flux of CO into the extratropical southern hemisphere is additionally enriched in 13C as a result of oxidation during transport. These effects partially offset the effect of highly depleted 13C/12C ratios in CO produced by CH4 oxidation. In the extratropical southern hemisphere, seasonal variation in the fraction of atmospheric CO derived from CH4 oxidation produces large changes in 13C/12 C which are partially offset by seasonal variations of surface sources. A good fit to observed average cycles can be obtained using surface source strengths consistent with previous estimates. However, the southern hemisphere data place strong constraints on the CH4 oxidation source and imply that either the CO yield per molecule of CH4 is about 0.7, compared with previous estimates of around 0.8, or that unidentified processes associated with CH4 oxidation cause 13C enrichment of about 4‰ in the CO produced.

Carbon monoxide budget in the northern hemisphere

To improve urban air quality the major industrialized nations of the West took steps during the 1970s and 1980s to reduce carbon monoxide (CO) emissions from automobiles and other industrial sources. Overall, CO/CO2 emission ratios from the mix of fossil fuel combustion sources have been reduced by about half during 1976–1990. Also, the tropospheric abundance of hydroxyl radical (OH), which is the main sink for CO, is proposed to have increased globally by about 1.0±0.8% yr−1 [Prinn et al., 1992]. We use a simple two‐box model to examine the impact of shrinking emissions and increasing OH on the global abundance of CO. We find that these factors contribute about equally in reducing CO levels in the Northern Hemisphere troposphere by about 1.8±0.8 ppb yr−1 on average.

Ocean to atmosphere carbon monoxide flux: Global inventory and climate implications

The global ocean to atmosphere flux of carbon monoxide (CO) is simulated with 4.5° × 7.5° latitude‐longitude spatial resolution using global data fields derived from an atmospheric general circulation model. The cloud and radiation package in the National Center for Atmospheric Research Community Climate Model is used to estimate the solar energy at the Earth's surface. This quantity is empirically related to photochemical interaction with dissolved organic matter, and the global concentration field of CO in surface seawater is estimated. Areas associated with the Intertropical Convergence Zone and mid‐ to high‐latitude winter hemisphere regions have relatively low climatological CO surface ocean concentrations on a local scale. The global surface wind and temperature fields are simultaneously used to calculate the global transfer velocity field of CO. Coupling these two computed fields, a global ocean to atmosphere CO flux of 165± 80 Tg yr−1 is proposed. The CO flux rates vary globally from 0.1 to 12 ug cm−2 month−1. The fluxes are largest in the mid‐latitude summer hemispheres, with a maximum at 40° S during the austral summer that is 40% larger on a zonal average than at any northern hemisphere latitude. Relatively small continental sources of CO to the southern hemisphere atmosphere and the short atmospheric residence time of this trace gas indicate that ocean‐derived CO may influence the local photochemical dynamics in the remote marine boundary layer of this region. A possible climate feedback scenario involving UV radiation, ozone, OH, and the air‐sea exchange of CO is proposed. The global ocean to atmosphere CO flux proposed here is at the high end of those used in previous atmospheric CO budgets. This estimate however must be considered a lower limit because no explicit simulation of global oceanic primary productivity is presently in the model.