A determination of the CH4, NO x and CO2 emissions from the Prudhoe Bay,Alaska oil development

In this paper we quantify the CH₄, CO₂ and NO _x emissions during routine operations at a major oil and gas production facility, Prudhoe Bay, Alaska, using the concentrations of combustion by products measured at the NOAA-CMDL observatory at Barrow, Alaska and fuel consumption data from Prudhoe Bay. During the 1989 and 1990 measurement campaigns, 10 periods (called events) were unambiguously identified where surface winds carry the Prudhoe Bay emissions to Barrow (approximately 300 km). The events ranged in duration from 8–48 h and bring ambient air masses containing substantially elevated concentrations of CH₄, CO₂ and NO _y to Barrow. Using the slope of the observed CH₄ vs CO₂ concentrations during the events and the CO₂ emissions based on reported fuel consumption data, we calculate annual CH₄ emissions of (24+/–8)×10³ metric tons from the facility. In a similar manner, the annual NO _x emissions are calculated to be (12+/–4)×10³ metric tons, which is in agreement with an independently determined value. The calculated CH₄ emissions represent the amount released during routine operations including leakage. However this quantity would not include CH₄ released during non-routine operations, such as from venting or gas flaring.     

Correlations among combustion effluent species at Barrow,Alaska: Aerosol black carbon,carbon dioxide,and methane

As part of the second Arctic Gas and Aerosol Sampling Program (AGASP II) continuous measurements of atmospheric aerosol black carbon (BC) were made at the NOAA/GMCC observatory at Barrow, Alaska (71°19N, 156°36W) during the period March 21–April 22, 1986. Black carbon is produced only by incomplete combustion of carbonaceous materials and so is a particularly useful atmospheric indicator of anthropogenic activities. The BC data have been analyzed together with the concurrent measurements of carbon dioxide (CO₂), methane (CH₄), and condensation nuclei (CN) that are routinely made at the observatory. All four species showed elevated and highly variable concentrations due to local human activities, principally in the township of Barrow, 7 km to the southwest, and at the DEW Line radar installation 1 km to the northwest. We distinguish between those periods of the record that are affected by local activities and those that are not, on the basis of the short-term (periods of up to 1 hour) variability of the continuous CO₂ and CN records, with large short-term variabilities indicating local sources. We identified seven periods of time (events) with durations ranging from 13 to 37 hours when the BC, CO₂, and CH₄ concentrations changed smoothly over time, were highly correlated with each other, and were not influenced by local activities. These events had BC/CO₂ ratios in the range (50–103)×10^–6. These ratios are dimensionless since we convert the CO₂ concentrations to units of ng m^–3 of carbon. Such values of BC/CO₂ are characteristic of the combustion effluent from large installations burning heavy fuel oil or coal, automobiles, and domestic-scale natural gas usage. We conclude that these events are indicative of air masses that have been polluted with combustion emissions in a distant location and then transported to the Arctic. In the absence of species-selective loss mechanisms, these air masses will maintain their combustion effluent signatures during the transport. The BC/CO₂ ratios found for the local combustion activities are consistent with those expected from known combustion processes.     

Kinetics of the reactions of hydroxyl radicals with alkyl nitrates and with some oxygen-containing organic compounds studied under simulated atmospheric conditions

Rate constants have been measured for the reactions of hydroxyl radicals with alkyl nitrates and with some oxygen-containing organic compounds by a competitive technique. Mixtures of synthetic air containing a few ppm of nitrous acid, ethylene and the organic substrate were photolysed in a Teflon bag smog chamber. Based on the value k _HO+C2H₄}=8.1×10^-12 cm³ molecule^-1 s^-1 the following rate constants were obtained for the hydroxyl radical reactions at 750 Torr and at 303 K in units of 10^-12 cm³ molecule^-1: CH₃ONO₂, 0.37±0.09; C₂H₅ONO₂, 0.48±0.20; n-C₃H₇ONO₂, 0.70±0.22; C₂H₅OH, 3.6±0.4; CH₃COCH₃, 0.26±0.08; CH₃CO₂ i-C₃H₇, 3.0±0.8; CH₃CO₂ n-C₃H₇, 2.4±0.2. The results are discussed in relation to the available literature data and the implications of the results are considered in terms of the smog reactivity of these molecules.     

Biomass burning in the tropical savannas of Ivory Coast: An overview of the field experiment Fire of Savannas (FOS/DECAFE 91)

FOS/DECAFE 91 (Fire of Savannas/Dynamique et Chimie Atmosphérique en Forêt Equatoriale) was the first multidisciplinary experiment organized in Africa to determine gas and aerosol emissions by prescribed savanna fires. The humid savanna of Lamto in Ivory Coast was chosen for its ecological characteristics representative of savannas with a high biomass density (900 g m^–2 dry matter). Moreover the vegetation and the climate of Lamto have been studied for more than twenty years. The emission ratios (X/CO₂) of the carbon compounds (CO₂, CO, NMHC, CH₄, PAH, organic acids and aerosols), nitrogen compounds (NO_x, N₂O, NH₃ and soluble aerosols) and sulfur compounds (SO₂, COS and aerosols) were experimentally determined by ground and aircraft measurements. To perform this experiment, 4 small plots (100×100 m) and 2 large areas (10×10 km) were prepared and burnt in January 1991 during the period of maximum occurrence of fires in this type of savanna. The detailed ecological study shows that the carbon content of the vegetation is constant within 1% (42 g C for 100 g of vegetal dry matter), the nitrogen content (0.29 g N for 100 g of dry matter) may vary by 10% and the sulfur content (0.05 g S/100 d.m.) by 20%. These variations of the biomass chemical content do not constitute an important factor in the variation of the gas and particle emission levels. With the emission ratios characteristic of humid savanna and flaming conditions (CO/CO₂ of 6.1% at the ground and 8% for airborne measurements), we propose a set of new emission factors, taking into account the burning efficiency which is about 80%: 74.4% of the carbon content of the savanna biomass is released to the atmosphere in the form of CO₂, 4.6% as CO, 0.2% as CH₄, 0.5% as NMHC and 0.7% as aerosols. 17.2% of the nitrogen content of the biomass is released as NO_x, 3.5% as N₂O, 0.6% as NH₃ and 0.5% as soluble aerosols.     

Henry's law coefficients of formic and acetic acids

The Henry's law constants, K _H, of dilute aqueous formic and acetic acids were determined experimentally as a function of concentration and temperature using a new counterflow packed-column technique. K _H was found to be (8.9±1.3)×10³ and (4.1±0.4)×10³ M atm^-1 at 25°C for HCOOH and CH₃COOH, respectively. The reaction enthalpies, H, were found to be –51±2 kJ mol^-1 and –52±1 kJ mol^-1 for formic and acetic acid, respectively. These are in good agreement with calculated thermochemical values.Whereas the K _H values are in reasonably good agreement with certain other experimentally determined values, K _H (HCOOH) is two to three times higher than calculated thermochemical values while K _H (CH₃COOH) is lower than the two calculated values.The best experimental values appear to be (11±2)×10³ M atm^-1 and (7±3)×10³ M atm^-1 for HCOOH and CH₃COOH, respectively.     

Carbonyl sulfide emissions from biomass burning in the tropics

Carbonyl sulfide emissions from biomass burning have been studied during field experiments conducted both in an African savanna area (Ivory Coast) and rice fields, central highland pine forest and savanna areas in Viet-Nam. During these experiments CO₂, CO and C₂H₂ or CH₄ have also been also monitored. COS values range from 0.6 ppbv outside the fires to 73 ppbv in the plumes. Significant correlations have been observed between concentrations of COS and CO (R ²=0.92,n=25) and COS and C₂H₂ (R ²=0.79,n=26) indicating a COS production during the smoldering combustion. COS/CO₂ emission factors (COS/CO₂) during field experiments ranged from 1.2 to 61×10^–6 (11.4×10^–6 mean value). COS emission by biomass burning was estimated to be up to 0.05 Tg S/yr in tropics and up to 0.07 Tg S/yr on a global basis, contributing thus about 10% to the global COS flux. Based on the S/C ratio measured in the dry plant biomass and the COS/CO₂ emission factor, COS can account for only about 7% of the sulfur emitted in the atmosphere by biomass burning.     

Production of N2O,CH4, and CO2 from soils in the tropical savanna during the dry season

Emissions of N₂O, CH₄, and CO₂ from soils at two sites in the tropical savanna of central Venezuela were determined during the dry season in February 1987. Measured arithmetic mean fluxes of N₂O, CH₄, and CO₂ from undisturbed soil plots to the atmosphere were 2.5×10⁹, 4.3×10¹⁰, and 3.0×10¹³ molecules cm^-2 s^-1, respectively. These fluxes were not significantly affected by burning the grass layer. Emissions of N₂O increased fourfold after simulated rainfall, suggesting that production of N₂O in savanna soils during the rainy season may be an important source for atmospheric N₂O. The CH₄ flux measurements indicate that these savanna soils were not a sink, but a small source, for atmospheric methane. Fluxes of CO₂ from savanna soils increased ninefold two hours after simulated rainfall, and remained three times higher than normal after 16 hours. More research is needed to clarify the significance of savannas in the global cycles of N₂O, CH₄, CO₂, and other trace gases, especially during the rainy season.     

Influence of Transport over a Mountain Ridge on the Chemical Composition of Marine Aerosols during the ACE-2 Hillcloud Experiment

Aerosol chemical composition and trace gas measurements were made at twolocations on the northeastern peninsula of Tenerife during the ACE-2HILLCLOUD experiment, between 28 June and 23 July 1997. Measurementswere made of coarse (#gt;2.5 m aerodynamic diameter) and fine (#lt; 2.5m) aerosol Cl^–, NO₃ ^–,SO₄ ^2–, non-sea saltSO₄ ^2– (NSSS),CH₃SO₃ ^– (MSA) andNH₄ ⁺, and gas phase dimethylsulphide (DMS), HCl,HNO₃, SO₂, CH₃COOH, HCOOH andNH₃. Size distributions were measured using a cascadeimpactor. Results show that in marine air masses NSSS and MSA wereformed via DMS oxidation, with additional NSSS present in air massescontaining a continental component. Using a Eulerian box model approachfor aerosols transported between upwind and downwind sites, a mean NSSSproduction rate of 4.36 × 10^–4 gm^–3 s^–1 was calculated for daytimeclear sky periods (highest insolation), with values for cloudy periodsduring daytime and nighttime of 3.55 × 10^–4 and2.40 × 10^–4 g m^–3s^–1, respectively. The corresponding rates for MSA were6.23 × 10^–6, 8.49 × 10^–6and 6.95 × 10^–6 g m^–3s^–1, respectively. Molar concentration ratios forMSA/NSSS were 8.7% (1.8–18.2%) and 1.9%(1.3–3.5%) in clean and polluted air masses, respectively.Reactions occurring within clouds appeared to have a greater influenceon rates of MSA production, than of NSSS, while conversely daytime gasphase reactions were more important for NSSS. For MSA, nighttimein-cloud oxidation rates exceeded rates of daytime gas phase productionvia OH oxidation of DMS. NSSS, MSA and ammonium had trimodal sizedistributions, with modes at 0.3, 4.0 and >10.0 m (NSSS andNH₄ ⁺), and 0.3, 1.5 and 4.0 m (MSA). Nosignificant production of other aerosol species was observed, with theexception of ammonium, which was formed at variable rates dependent onneutralisation of the aerosol with ammonia released from spatiallynon-uniform surface sources. Seasalt components were mainly present incoarse particles, although sub-micrometre chloride was also measured.Losses by deposition exceeded calculated expectations for all species,and were highest for the seasalt fraction and nitrate.     

Field study of the emissions of methyl chloride and other halocarbons from biomass burning in Western Africa

A field study of trace gas emissions from biomass burning in Equatorial Africa gave methyl chloride emission ratios of 4.3×10^–5±0.8×10^–5 mol CH₃Cl/mol CO₂. Based on the global emission rates for CO₂ from biomass burning we estimate a range of 226–904×10⁹ g/y as global emission rate with a best estimate of 515×10⁹ g/y. This is somewhat lower than a previous estimate which has been based on laboratory studies. Nevertheless, our emission rate estimates correspond to 10–40% of the global turnover of methyl chloride and thus support the importance of biomass burning as methyl chloride source. The emission ratios for other halocarbons (CH₂Cl₂, CHCl₃, CCl₄, CH₃CCl₃, C₂HCl₃, C₂Cl₄, F-113) are lower. In general there seems to be a substantial decrease with increasing complexity of the compounds and number of halogen atoms. For dichloromethane biomass burning still contributes significantly to the total global budget and in the Southern Hemisphere biomass burning is probably the most important source for atmospheric dichloromethane. For the global budgets of other halocarbons biomass burning is of very limited relevance.     

Influences on surface energy fluxes in simulated present and doubled CO2 climates

The surface energy fluxes simulated by the CSIRO9 Mark 1 GCM for present and doubled CO₂ conditions are analyzed. On the global scale the climatological flux fields are similar to those from four GCMs studied previously. A diagnostic calculation is used to provide estimates of the radiative forcing by the GCM atmosphere. For 1 × CO₂, in the global and annual mean, cloud produces a net cooling at the surface of 31 W m^–2. The clear-sky longwave surface greenhouse effect is 311 W m^–2, while the corresponding shortwave term is –79 W m^–2. As for the other GCM results, the CSIRO9 CO₂ surface warming (global mean 4.8°C) is closely related to the increased downward longwave radiation (LW ). Global mean net cloud forcing changes little. The contrast in warming between land and ocean, largely due to the increase in evaporative cooling (E) over ocean, is highlighted. In order to further the understanding of influences on the fluxes, simple physically based linear models are developed using multiple regression. Applied to both 1 × CO₂ and CO₂ December–February mean tropical fields from CSIRO9, the linear models quite accurately (3–5 W m^–2 for 1 × CO₂ and 2–3 W m^–2 for CO₂) relate LW and net shortwave radiation to temperature, surface albedo, the water vapor column, and cloud. The linear models provide alternative estimates of radiative forcing terms to those from the diagnostic calculation. Tropical mean cloud forcings are compared. Over land, E is well correlated with soil moisture, and sensible heat with air-surface temperature difference. However an attempt to relate the spatial variation of LWt within the tropics to that of the nonflux fields had little success. Regional changes in surface temperature are not linearly related to, for instance, changes in cloud or soil moisture.     

Kinetics of the Gas-Phase Reactions of OH Radicals, NO3 Radicals and O3 with Three C7-Carbonyls Formed From The Atmospheric Reactions of Myrcene, Ocimene and Terpinolene

Rate constants for the gas-phase reactions of OH radicals, NO₃ radicals and O₃ with the C₇-carbonyl compounds 4-methylenehex-5-enal [CH₂=CHC(=CH₂)CH₂CH₂CHO], (3Z)- and (3E)-4-methylhexa-3,5-dienal [CH₂=CHC(CH₃)=CHCH₂CHO] and 4-methylcyclohex-3-en-1-one, which are products of the atmospheric degradations of myrcene, Z- and E-ocimene and terpinolene, respectively, have been measured at 296 ± 2 K and atmospheric pressure of air using relative rate methods. The rate constants obtained (in cm³ molecule^–1 s^–1 units) were: for 4-methylenehex-5-enal, (1.55 ± 0.15) × 10^–10, (4.75 ± 0.35) × 10^–13 and (1.46 ± 0.12) × 10^–17 for the OH radical, NO₃ radical and O₃ reactions, respectively; for (3Z)-4-methylhexa-3,5-dienal: (1.61 ± 0.35) × 10^–10, (2.17 ± 0.30) × 10^–12, and (4.13 ± 0.81) × 10^–17 for the OH radical, NO₃ radical and O₃ reactions, respectively; for (3E)-4-methylhexa-3,5-dienal: (2.52 ± 0.65) × 10^–10, (1.75 ± 0.27) × 10^–12, and (5.36 ± 0.28) × 10^–17 for the OH radical, NO₃ radical and O₃ reactions, respectively; and for 4-methylcyclohex-3-en-1-one: (1.10 ± 0.19) × 10^–10, (1.81 ± 0.35) × 10^–12, and (6.98 ± 0.40) × 10^–17 for the OH radical, NO₃ radical and O₃ reactions, respectively. These carbonyl compounds are all reactive in the troposphere, with daytime reaction with the OH radical and nighttime reaction with the NO₃ radical being predicted to dominate as loss processes and with estimated lifetimes of about an hour or less.     

GREENHOUSE GASES FROM DEFORESTATION IN BRAZILIAN AMAZONIA: NET COMMITTED EMISSIONS

Deforestation in Brazilian Amazonia is a significant source of greenhouse gases today and, with almost 90% of the originally forested area still uncleared, is a very large potential source of future emissions. The 1990 rate of loss of forest (13.8 × 10³ km²/year) and cerrado savanna (approximately 5 × 10³ km²/year) was responsible for releasing approximately 261 × 10⁶ metric tons of carbon (10⁶ t C) in the form of CO2, or 274–285 × 10⁶ t of CO2-equivalent C considering IPCC 1994 global warming potentials for trace gases over a 100-year horizon. These calculations consider conversion to a landscape of agriculture, productive pasture, degraded pasture, secondary forest, and regenerated forest in the proportions corresponding to the equilibrium condition implied by current land-use patterns. Emissions are expressed as net committed emissions, or the gases released over a period of years as the carbon stock in each hectare deforested approaches a new equilibrium in the landscape that replaces the original forest. For low and high trace gas scenarios, respectively, 1990 clearing produced net committed emissions (in 10⁶ t of gas) of 957–958 for CO2, 1.10–1.42 for CH₄, 28–35 for CO, 0.06–0.16 for N₂O, 0.74–0.74 for NO_x and 0.58–1.16 for non-methane hydrocarbons.     

Emission of nitrogen oxides (NO x ) from a flooded soil fertilized with urea: Relation to other nitrogen loss processes

Emissions of nitric oxide and other odd nitrogen oxides (NO _x ) from a flooded rice field were studied after urea had been broadcast into the floodwater.The NO _x flux from the fertilized area was very low (0.2×10^-9 g N m^-2 s^-1) for the first few days after application of urea and was high (0.95×10^-9 g N m^-2 s^-1) in the subsequent period when significant nitrite and nitrate were present in the floodwater. At night, little if any NO _x was exhaled but ambient NO₂ was absorbed by the floodwater. An uptake velocity for NO₂ of 3×10^-4 m s^-1 was measured during one night. Maximum NO _x losses were observed near 1300 h when temperature and solar ultraviolet light were maximum.While the amounts of nitrogen oxides emitted are of little agronomic importance (2×10^-3 per cent of the fertilizer nitrogen was lost as NO _x during the 10-day study period), they may well be of significance as a source for some gas reactions in the atmosphere and for the global nitrogen cycle.Of the fertilizer nitrogen applied (as urea) approximately 30% was lost to the atmosphere by NH₃ volatilization, 15% by denitrification, presumably as N₂, and the remainder, less minor losses of NO and N₂O, remained in the plant/soil/water system.Now at Forestry Department, Australian National University, G.P.O. Box 4, ACT 2601, Australia.     

Numerical integration errors in calculated tropospheric photodissociation rate coefficients

Tropospheric photodissociation rate coefficients (J values) were calculated for NO₂, O₃, HNO₂, CH₂O, and CH₃CHO using high spectral resolution (0.1 mm wavelength increments), and compared to the J values obtained with numerically degraded resolution (=1, 2, 4, 6, 8, and 10 nm, and several commonly used nonuniform grids). Depending on the molecule, substantial errors can be introduced by the larger increments. Thus for =10 nm, errors are less than 1% for NO₂, less than 2% for HNO₂, +6.5% to -16% for CH₂O, -6.9% to +24% for CH₃CHO, and -24% to +110% for O₃. The errors for CH₂O arise from the fine structure of its absorption spectrum, and are prevalently negative (underestimate of J). The errors for O₃, and to a lesser extent for CH₃CHO, arise mainly from under-resolving the overlap of the molecular action spectrum and the tropospheric actinic flux in the wavelength region of stratospheric ozone attenuation. The sign of those errors depends on whether the actinic flux is averaged onto the grid before or after the radiative transfer calculation. In all cases studied, grids with 2 nm produced errors no larger than 5%.     

Methane emissions from a landfill measured by eddy correlation using a fast response diode laser sensor

We describe a fast response methane sensor based on the absorption of radiation generated with a near-infrared InGaAsP diode laser. The sensor uses an open path absorption region 0.5 m long; multiple pass optics provide an optical path of 50 m. High frequency wavelength modulation methods give stable signals with detection sensitivity (S/N=1, 1 Hz bandwidth) for methane of 65 ppb at atmospheric pressure and room temperature. Improvements in the optical stability are expected to lower the current detection limit. We used the new sensor to measure, by eddy correlation, the CH₄ flux from a clay-capped sanitary landfill. Simultaneously we measured the flux of CO₂ and H₂O. From seven half-hourly periods of data collected after a rainstorm on November 23, 1991, the average flux of CH₄ was 17 mmol m^–2 hr^–1 (6400 mg CH₄ m^–2 d^–1) with a coefficient of variation of 25%. This measurement may underrepresent the flux by 15% due to roll-off of the sensor response at high frequency. The landfill was also a source of CO₂ with an average flux of 8.1 mmol m^–2 hr^–1 (8550 mg CO₂ m^–2 d^–1) and a coefficient of variation of 26%. A spectral analysis of the data collected from the CH₄, CO₂, and H₂O sensors showed a strong similarity in the turbulent transfer mechanisms.     

The Henry's Law Constants of the Haloacetic Acids

Henry's law constants K_H (mol kg^-1 atm^-1) have been measured between 278.15 K and 308.15 K for the following organic acids: CH₂FCOOH (ln(K_H[298.15 K]) = 11.3 ± 0.2), CH₂ClCOOH (11.59 ± 0.14), CH₂BrCOOH (11.94 ± 0.21), CHF₂COOH (10.32 ± 0.10), CHCl₂COOH (11.69 ± 0.11), CHBr₂COOH (12.33 ± 0.29), CBr₃COOH (12.61 ± 0.21), and CClF₂COOH (10.11 ± 0.12). The variation of K_H with temperature was determined for all acids except CH₂FCOOH and CBr₃COOH, with _r H° for the dissolution reaction ranging from –85.2 ± 2.6 to –57.1 ± 2.5 kJ mol^-1, meaning that their solubility is generally more sensitive to temperature than is the case for the simple carboxylic acids. The Henry's law constants show consistent trends with halogen substitution and, together with their high solubility compared to the parent (acetic) acid (ln(K_H[298.15 K]) = 8.61), present a severe test of current predictive models based upon molecular structure. The solubility of haloacetic acids and strong dissociation at normal pH mean that they will partition almost entirely into cloud and fog in the atmosphere (0.05–1.0 g H₂O m^-3), but can reside in both phases for the liquid water contents typical of aerosols (10^-5-10^-4 g H₂O m^-3).     

Trace gas measurements at the monitoring station cape point,South Africa,between 1978 and 1988

Since 1978, a measuring station has been operated at Cape Point (34°21 S, 18°29 E). In this article, results of measurements of CO, CFCl₃, CCl₄, O₃, N₂O and CH₄ are presented as monthly means and analyzed with respect to long-term trends and seasonal variations. For CO and CH₄, very similar seasonal variations have been observed, indicating strong interrelations between these two gases. For CO and O₃, no significant changes of the mean annual concentrations can be established for the observation periods of 10 and 5 years, respectively. The measurements yield a growth rate of 9.1 pptv yr^-1 for CFCl₃ (1980–1987) and 0.6 ppbv yr^-1 for N₂O (1983–1987). The concentration increases of CH₄ (10.3 ppbv yr^-1 for 1983–1987) and of CCl₄ (2.1 pptv yr^-1 for 1980–1988) are analyzed for temporal changes during the last years.Presented at the Second Conference on Baseline Observations in Atmospheric Chemistry (SABOAC II) in Melbourne, Australia, November 1988.     

On the Exchange of NO3 Radicals with Aqueous Solutions: Solubility and Sticking Coefficient

The exchange of NO₃ radicals with the aqueous-phase was investigated at room temperature (293 K) in a series of wetted denuders. From these experiments, the uptake coefficient of NO₃ was determined on 0.1 M NaCl solutions and was found to be (NO₃) 2 × 10^-3 in good agreement with recent studies. The Henry coefficient of NO₃ was estimated to be K_H(NO₃) = 1.8 M · atm^-1, with a (2) uncertainty of ±3 M · atm^-1. From the upper limit for the Henry coefficient (K_H = 5 M · atm^-1) and available thermodynamic data, the redox potential of dissolved NO₃/NO ₃ ^– is estimated to be in the range of 2.3 to 2.5 V. This range is at the lower boundary of earlier estimates. The results are discussed in the light of a recent publication. Based on our data and a model of the transport and chemistry in the liquid film, an upper limit is derived for the product of the Henry coefficient K_H and the rate coefficient k ₁₀ of the potential reaction NO₃ + H₂O HNO₃ + OH. For K_H = 0.6 M · atm^-1, we find k ₁₀ < 0.05 s^-1 · atm^-1, i.e., about 100 times smaller than what was suggested by Rudich and co-workers. Because of its small solubility, heterogeneous removal of NO₃ is only important under conditions where the dissolved NO₃ is removed quickly from equilibrium, for example by reactions with Cl^– or HSO ₃ ^– ions in the liquid-phase. Otherwise, heterogenous removal should mainly proceed via N₂O₅.     

The Reactivity of Biogenic Monoterpenes towards OH· and SO4-· Radicals in De-Oxygenated Acidic Solution

The reactivity of some selected biogenic monoterpenecompounds towards important aqueous phase free-radicaloxidants, namely OH· and SO₄ ^-·, have beeninvestigated using the complementary experimentaltechniques of pulse radiolysis and laser flashphotolysis ( = 248 nm). Rate constants forthe reactions of the OH· radical with cis-verbenol andmethacrolein have been determined to be (6.8 ± 0.5) ×10⁹ dm³ mol^-1 s^-1 and (8.0± 0.7) × 10⁹ dm³ mol^-1s^-1,respectively (T = 20 °C, pH 4.0, Ionic strength 0 mol dm^-3). Rate constants and activationenergies for the reactions of the SO₄ ^-·radical have been measured for the following compounds(T = 20 °C, pH 4.0, Ionic strength = 0.03 moldm^-3): -pinene (k = (3.1 ± 0.1) ×10⁹ dm³ mol^-1 s^-1;E _act. =(8.9 ± 1.3) kJ mol^-1), -terpineol(k = (4.1 ± 0.1) × 10⁹ dm³mol^-1s^-1; E _act. = (13.4 ± 0.6) kJmol^-1), cis-verbenol (k = (3.2 ± 0.2) ×10⁹ dm³ mol^-1 s^-1;E _act. =(10.0 ± 0.7) kJ mol^-1), verbenone (k = (1.6± 0.1) × 10⁹ dm³ mol^-1s^-1;E _act. = (6.1 ± 0.7) kJ mol^-1), myrtenal(k = (1.85 ± 0.1) × 10⁹ dm³mol^-1s^-1; E _act. = (7.5 ± 0.7) kJmol^-1)and methacrolein (k = (1.18 ± 0.1) × 10⁹dm³ mol^-1 s^-1). In most instances theabsorption spectra of the intermediate products formedby these reactions have been measured which, inconjunction with strategic conductiometric studies,have been used to suggest plausible mechanisms for theoxidation in acidic de-oxygenated solution.     

Airborne measurements of savanna fire emissions and the regional distributio of pyrogenic pollutants over Western Africa

We measured CO₂, CO, CH₄, H₂, and NO₂ in air masses polluted by savanna fires over Côte d'Ivoire, western Africa. Elevated concentrations of these trace gases were found in fire plumes and also in extensive haze layers. Trace gas mixing ratios ranged as high as 605 ppmv for CO₂, 14.8 ppmv for CO, 2.7 ppmv for CH₄, 4.2 ppmv for H₂, and 25 ppbv for NO₂. We compare our emission ratios to those obtained in previous field and laboratory studies. The emission ratios, expressed as an average and as a range or as an average only, were: dCO/dCO₂ 5.3×10^–2 (3–18×10^–2); dCH₄/dCO 5.3×10^–2; dH₂/dCO 2.4×10^–1 and dNO₂/dCO₂ 1.8×10^–4 (1.5–2.2×10^–4). The values found match those found during similar measurements, though our results point to rather vigorous burning in the savanna of western Africa.