Trace gas variations at Cape Point,South Africa,during May 1997 following a regional biomass burning episode

During the continuous monitoring of atmospheric parameters at the station Cape Point (34°S, 18°E), a smoke plume originating from a controlled fire of 30-yr-old fynbos was observed on 6 May 1997. For this episode, which was associated with a nocturnal inversion and offshore airflow, atmospheric parameters (solar radiation and meteorological data) were considered and the levels of various trace gases compared with those measured at Cape Point in maritime air. Concentration maxima in the morning of 6 May for CO₂, CO, CH₄ and O₃ amounted to 370.3 ppm, 491 ppb, 1730 ppb and 47 ppb, respectively, whilst the mixing ratios of several halocarbons (F-11, F-12, F-113, CCl₄ and CH₃CCl₃) remained at background levels. In the case of CO, the maritime background level for this period was exceeded by a factor of 9.8. Differences in ozone levels of up to 5 ppb between air intakes at 4 and 30 m above the station (located at 230 m above sea level) indicated stratification of the air advected to Cape Point during the plume event. Aerosols within the smoke plume caused the signal of global solar radiation and UV–A to be attenuated from 52.4 to 13.0 mW cm⁻² and from 2.3 to 1.3 mW cm⁻², respectively, 5 h after the trace gases had reached their maxima. Emission ratios (ERs) calculated for CO and CH₄ relative to CO₂ mixing ratios amounted to 0.042 and 0.0040, respectively, representing one of the first results for fires involving fynbos. The CO ER is somewhat lower than those given in the literature for African savanna fires (average ER=0.048), whilst for CH₄ the ER falls within the range of ERs reported for the flaming (0.0030) and smouldering phases (0.0055) of savanna fires. Non-methane hydrocarbon (NMHC) data obtained from a grab sample collected during the plume event were compared to background levels. The highest ERs (ΔNMHC/ΔCH₄) have been obtained for the C₂–C₃ hydrocarbons (e.g. ethene at 229.3 ppt ppb⁻¹), whilst the C₄–C₇ hydrocarbons were characterised by the lowest ERs (e.g. n-hexane at 1.0 and n-pentane at 0.8 ppt ppb⁻¹).     

Biomass consumption and CO2, CO and main hydrocarbon gas emissions in an Amazonian forest clearing fire

Biomass consumption and CO₂, CO and hydrocarbon gas emissions in an Amazonian forest clearing fire are presented and discussed. The experiment was conducted in the arc of deforestation, near the city of Alta Floresta, state of Mato Grosso, Brazil. The average carbon content of dry biomass was 48% and the estimated average moisture content of fresh biomass was 42% on wet weight basis. The fresh biomass and the amount of carbon on the ground before burning were estimated as 528 t ha^?1 and 147 t ha^?1, respectively. The overall biomass consumption for the experiment was estimated as 23.9%. A series of experiment in the same region resulted in average efficiency of 40% for areas of same size and 50% for larger areas. The lower efficiency obtained in the burn reported here occurred possibly due to rain before the experiment. Excess mixing ratios were measured for CO₂, CO, CH₄, C₂–C₃ aliphatic hydrocarbons, and PM_2.5. Excess mixing ratios of CH₄ and C₂–C₃ hydrocarbons were linearly correlated with those of CO. The average emission factors of CO₂, CO, CH₄, NMHC, and PM_2.5 were 1,599, 111.3, 9.2, 5.6, and 4.8 g kg^?1 of burned dry biomass, respectively. One hectare of burned forest released about 117,000 kg of CO₂, 8100 kg of CO, 675 kg of CH₄, 407 kg of NMHC and 354 kg of PM_2.5.     

Shouldn’t snowpacks be sources of monocarboxylic acids?

We report the first measurements of the mixing ratios of acetic (CH₃COOH) and formic (HCOOH) acids in the air filling the pore spaces of the snowpacks (firn air) at Summit, Greenland and South Pole. Both monocarboxylic acids were present at levels well above 1 ppbv throughout the upper 35 cm of the snowpack at Summit. Maximum mixing ratios in Summit firn air reached nearly 8 ppbv CH₃COOH and 6 ppbv HCOOH. At South Pole the mixing ratios of these acids in the top 35 cm of firn air were also generally >1 ppbv, though their maximums barely exceeded 2.5 ppbv of CH₃COOH and 2.0 ppbv of HCOOH. Mixing ratios of the monocarboxylic acids in firn air did not consistently respond to diel and experimental (fast) variations in light intensity, unlike the case for N oxides in the same experiments. Air-to-snow fluxes of CH₃COOH and HCOOH apparently support high mixing ratios (means of (CH₃COOH/HCOOH) 445/460 and 310/159 pptv at Summit and South Pole, respectively) in air just above the snow during the summer sampling seasons at these sites. We hypothesize that oxidation of carbonyls and alkenes (that are produced by photo- and OH-oxidation of ubiquitous organic compounds) within the snowpack is the source of the monocarboxylic acids.     

Recent atmospheric Pb deposition at a rural site in southern Germany assessed using a peat core and snowpack,and comparison with other archives

In a peat bog from Black Forest, Southern Germany, the rate of atmospheric Pb accumulation was quantified using a peat core dated by ²¹⁰Pb and ¹⁴C. The most recent Pb accumulation rate (2.5 mg m⁻² y⁻¹) is similar to that obtained from a snowpack on the bog surface, which was sampled during the winter 2002 (1 to 4 mg m⁻² y⁻¹). The Pb accumulation rates recorded by the peat during the last 25 yr are also in agreement with published values of direct atmospheric fluxes in Black Forest. These values are 50 to 200 times greater than the “natural” average background rate of atmospheric Pb accumulation (20 μg m⁻² y⁻¹) obtained using peat samples from the same bog dating from 3300 to 1300 cal. yr B.C. The isotopic composition of Pb was measured in both the modern and ancient peat samples as well as in the snow samples, and clearly shows that recent inputs are dominated by anthropogenic Pb. The chronology and isotopic composition of atmospheric Pb accumulation recorded by the peat from the Black Forest is similar to the chronologies reported earlier using peat cores from various peat bogs as well as herbarium samples of Sphagnum and point to a common Pb source to the region for the past 150 years. In contrast, Pb contamination occurring before 1850 in southwestern Germany, differs from the record published for Switzerland mainly due to the mining activity in Black Forest. Taken together, the results show that peat cores from ombrotrophic bogs can yield accurate records of atmospheric Pb deposition, provided that the cores are carefully collected, handled, prepared, and analysed using appropriate methods.     

Air–land exchanges of CO2, CH4 and N2O measured by FTIR spectrometry and micrometeorological techniques

Micrometeorological flux-gradient and nocturnal boundary layer methods were combined with Fourier transform infrared (FTIR) spectroscopy for high-precision trace gas analysis to measure fluxes of the trace gases CO₂, CH₄ and N₂O between agricultural fields and the atmosphere. The FTIR measurements were fully automated and routinely obtained a precision of 0.1–0.2% for several weeks during a measurement campaign in October 1995. In flux-gradient measurements, vertical profiles of the trace gases were measured every 30 min from the ground to 22 m. When combined with independent micrometeorological measurements of water vapour fluxes, trace gas fluxes from the underlying surface could be determined. In the nocturnal boundary layer method the rate of change in mass storage in the 0–22 m layer was combined with fluxes measured at 22 m to estimate surface fluxes. Daytime fluxes for CO₂ were −0.78±0.40 (1σ) mg CO₂ m⁻² s⁻¹. Daytime fluxes of N₂O and CH₄ were very small and difficult to measure reliably using the flux-gradient technique, despite the high precision of the concentration measurements. Mean daytime flux for N₂O was 17±48 ng N m⁻² s⁻¹, while the corresponding flux for CH₄ was 47±410 ng CH₄ m⁻² s⁻¹. The mean nighttime flux of CO₂ estimated using the nocturnal boundary layer method was +0.15±0.05 mg CO₂ m⁻² s⁻¹, in good agreement with chamber measurements of respiration rates. Nighttime fluxes of CH₄ and N₂O from the nocturnal boundary layer method were 109±69 ng CH₄ m⁻² s⁻¹ and 2±3.2 ng N m⁻² s⁻¹, respectively, in good agreement with chamber measurements and inventory estimates based on the sheep and cattle stocking rates in the region. The suitability of FTIR-based methods for long term monitoring of spatially and temporally averaged flux measurements is discussed.     

Properties of organic matter in PM2.5 at Changdao Island,China—A rural site in the transport path of the Asian continental outflow

Fifty-five seasonal PM_2.5 samples were collected March 2003–January 2004 at Changdao, a resort island located at the demarcation line between Bohai Sea and Yellow Sea in Northern China. Changdao is in the transport path of the continental aerosols heading toward the Pacific Ocean in winter and spring due to the East Asia Monsoon. Solvent-extractable organic compounds (SEOC), organic carbon (OC), elemental carbon (EC) and water-soluble organic carbon (WSOC) were analyzed for source identification based on molecular markers. This data set provides useful information for the downstream site researchers of the Asian continental outflow. Total carbon (TC, OC+EC) was ∼18 μg m⁻³ in winter, ∼9 μg m⁻³ in spring and autumn and a large part of the TC was WSOC (33% in winter, >45% in the other seasons). Winter and spring were the high SEOC seasons with n-fatty acids the highest at ∼290 and ∼170 ng m⁻³, respectively, followed by n-alkanes at ∼210 and ∼90 ng m⁻³, and polycyclic aromatic hydrocarbons (PAHs) were also at high at ∼120 and ∼30 ng m⁻³. High WSOC/TC, low C_18:1/C₁₈ of fatty acids, and low concentrations of labile PAHs such as benzo(a)pyrene, together with back trajectory analysis suggested that the aerosols were aged and transported. PAHs, triterpane and sterane distributions provided evidence that coal burning was the main source of the continental outflow. The detection of levoglucosan and β-sitosterol in nearly all the samples showed the impact of biomass burning.     

Methane emissions from lakes and floodplains in Pantanal,Brazil

To evaluate the tropical wetlands contribution to the methane (CH₄) burden better, field campaigns were performed during 2004 and 2005 near the Miranda River, in five sites inside the Brazilian Pantanal region. The CH₄ fluxes were determined using the static chamber technique. Environmental variables that may affect CH₄ emissions, as the water depth, the water and air temperatures were also measured. The overall average of the 320 individual CH₄ flux measurements made between March/2004 and March/2005 was 142±314 mg CH₄ m⁻² d⁻¹, which is a value near the ones observed in other tropical flooded regions. About 47% of the fluxes measurements presented nonlinear increases in the chamber concentrations, which were assumed to be linked to CH₄ losses through bubbles. The bubble flux represented about 90% of the total CH₄ losses in the measurements and ranged from 1 to 2187 mg CH₄ m⁻² d⁻¹ with an average of 292±410 mg CH₄ m⁻² d⁻¹ (median: 153 mg CH₄ m⁻² d⁻¹). The diffusive flux ranged from 1 to 124 mg CH₄ m⁻² d⁻¹, with an average of 10±17 mg CH₄ m⁻² d⁻¹ (median: 5 mg CH₄ m⁻² d⁻¹). The fluxes from lakes were smaller than those observed in the floodplains, where the flooding was more dependent on the seasonal cycle. The diffusive flux showed a slight, but not statistically significant seasonal variation, following the seasonal variation of the flooding of the Pantanal region. A rough estimative of the total annual CH₄ emission shows that the contribution of the Pantanal is about 3.3 Tg CH₄ yr⁻¹, which represents about 3.3% of the total CH₄ emissions estimated to be originated in wetlands ecosystems. It may be a conservative estimate, which may present a large interannual variation, since it was obtained during one of the lowest flood of the Pantanal in recent years.     

China's grazed temperate grasslands are a net source of atmospheric methane

A budget for the methane (CH₄) cycle in the Xilin River basin of Inner Mongolia is presented. The annual CH₄ budget in this region depends primarily on the sum of atmospheric CH₄ uptake by upland soils, emission from small wetlands, and emission from grazing ruminants (sheep, goats, and cattle). Flux rates for these processes were averaged over multiple years with differing summer rainfall. Although uplands constitute the vast majority of land area, they consume much less CH₄ per unit area than is emitted by wetlands and ruminants. Atmospheric CH₄ uptake by upland soils was ?3.3 and ?4.8 kg CH₄ ha^?1 y^?1 in grazed and ungrazed areas, respectively. Average CH₄ emission was 791.0 kg CH₄ ha^?1 y^?1 from wetlands and 8.6 kg CH₄ ha^?1 y^?1 from ruminants. The basin area-weighted average of all three processes was 6.8 kg CH₄ ha^?1 y^?1, indicating that ruminant production has converted this basin to a net source of atmospheric CH₄. The total CH₄ emission from the Xilin River basin was 7.29 Gg CH₄ y^?1. The current grazing intensity is about eightfold higher than that which would result in a net zero CH₄ flux. Since grazing intensity has increased throughout western China, it is likely that ruminant production has converted China's grazed temperate grasslands to a net source of atmospheric CH₄ overall.     

Greenhouse gas emissions from penguin guanos and ornithogenic soils in coastal Antarctica: Effects of freezing–thawing cycles

In coastal Antarctica, freezing and thawing influence many physical, chemical and biological processes for ice-free tundra ecosystems, including the production of greenhouse gases (GHGs). In this study, penguin guanos and ornithogenic soil cores were collected from four penguin colonies and one seal colony in coastal Antarctica, and experimentally subjected to three freezing–thawing cycles (FTCs) under ambient air and under N₂. We investigated the effects of FTCs on the emissions of three GHGs including nitrous oxide (N₂O), carbon dioxide (CO₂) and methane (CH₄). The GHG emission rates were extremely low in frozen penguin guanos or ornithogenic soils. However, there was a fast increase in the emission rates of three GHGs following thawing. During FTCs, cumulative N₂O emissions from ornithogenic soils were greatly higher than those from penguin guanos under ambient air or under N₂. The highest N₂O cumulative emission of 138.24 μg N₂O–N kg^?1 was observed from seal colony soils. Cumulative CO₂ and CH₄ emissions from penguin guanos were one to three orders of magnitude higher than those from ornithogenic soils. The highest cumulative CO₂ (433.0 mgCO₂–C kg^?1) and CH₄ (2.9 mgCH₄–C kg^?1) emissions occurred in emperor penguin guanos. Penguin guano was a stronger emitter for CH₄ and CO₂ while ornithogenic soil was a stronger emitter for N₂O during FTCs. CO₂ and CH₄ fluxes had a correlation with total organic carbon (TOC) and soil/guano moisture (M_c) in penguin guanos and ornithogenic soils. The specific CO₂–C production rate (CO₂–C/TOC) indicated that the bioavailability of TOC was markedly larger in penguin guanos than in ornithogenic soils during FTCs. This study showed that FTC-released organic C and N from sea animal excreta may play a significant role in FTC-related GHG emissions, which may account for a large proportion of annual fluxes from tundra ecosystems in coastal Antarctica.     

The performance of a gas and aerosol monitoring system (GAMS) for the determination of acidic water soluble organic and inorganic gases and ammonia as well as related particles from the atmosphere

A new application of the quasi-simultaneous gas/particle phase sampling and analysis principle first proposed by Simon and Dasgupta (Anal. Chem. 34 (1995) 71) is described. For the first time, a gradient chromatograph is used in connection with such a sampling system to allow the simultaneous determination of major organic (formic, acetic, propionic, oxalic, malonic and succinic) and inorganic (SO₂, HNO₂, HNO₃, HCl and H₂F₂) acidic gases and related particles. Another addition to the previous systems is the analysis of cations other than ammonium from the particulate phase. The time resolution of the instrument still remains high, 1 h, during which gaseous water-soluble acidic compounds, ammonia, as well as related anionic particles and inorganic major cations are analysed. Sampling is based on diffusion in a wetted parallel plate denuder for gases and on growth in supersaturated water vapour for particles. The determination limits range from 2 ppt (acetate) to 0.4 ppb (ammonia) in the gas phase and 0.01 μg m⁻³ (citric acid) to 0.79 μg m⁻³ (calcium) for particulate matter. Collection efficiencies for gas and aerosol sampling were quantified and the supersaturation in the aerosol sampling apparatus investigated. The system has been used for field measurements at a background station; selected results of these measurements are presented.     

Identification,abundance and origin of atmospheric organic particulate matter in a Portuguese rural area

Respirable suspended particles high-volume samples were collected from a coastal-rural site in the centre of Portugal in August 1997 and their solvent-extractable organic compounds were subjected to characterisation by gas chromatography-mass spectrometry. Particles were also analysed by a thermal/optical technique in order to determine their black and organic carbon content. The total lipid extract yields ranged from 20 to 63 μg m⁻³, containing mainly aliphatic hydrocarbons such as n-alkanes, acids, alcohols, aldehydes, ketones and polycyclic aromatic hydrocarbons. The higher input of vascular plant wax components was demonstrated by the distribution patterns of the n-alkanes, n-alkanoic acids and n-alkanols homologous series, with C_max at C₂₉, C₂₂/C₂₄ and C₃₀, respectively. The CPI values for these series were in the range 1.8–9.7, being indicative of recent biogenic input from microbial lipid residues and flora epicuticular components. Specific natural constituents (e.g. phytosterols, terpenes, etc.) were identified as molecular markers. Some oxidation products from volatile organic precursors were also present in the aerosols. In addition, all samples had a component of petroleum hydrocarbons representing urban and vehicular emissions probably transported from the nearest cities and from the motorway in the vicinity. This data set could be used to make a mass balance with organic carbon, organic extracts and elutable matter, permitting also the comparison with lipid signatures observed for other regions.     

Extent of H-atom abstraction from OH + p-cymene and upper limits to the formation of cresols from OH + m-xylene and OH + p-cymene

Aromatic hydrocarbons are important constituents of vehicle exhaust and of non-methane volatile organic compounds in ambient air in urban areas. It has recently been proposed that dealkylation is a significant pathway for the OH radical-initiated reactions, leading to the formation of phenolic compounds and/or oxepins (Noda, J., Volkamer, R., Molina, M.J., 2009. Dealkylation of alkylbenzenes: a significant pathway in the toluene, o-, m-, and p-xylene + OH reaction. Journal of Physical Chemistry A 113, 9658–9666.). We have investigated the formation of cresols from the reactions of OH radicals with m-xylene and p-cymene, and obtain upper limits of <1% for formation of each cresol isomer from OH + m-xylene and <2% for formation of each cresol isomer from OH + p-cymene. In addition, we have measured the formation yield of 4-methylacetophenone (the major product formed subsequent to H-atom abstraction from the CH(CH₃)₂ group) in the OH + p-cymene reaction to be 14.8 ± 3.2%, and estimate that H-atom abstraction from the CH₃ and CH(CH₃)₂ groups in p-cymene accounts for 20 ± 4% of the overall OH radical reaction. We also used a relative rate technique to measure the rate constant for the reaction of OH radicals with 4-methylacetophenone to be (4.50 ± 0.43) × 10^?12 cm³ molecule^?1 s^?1 at 297 ± 2 K.     

Winter-grazing reduces methane uptake by soils of a typical semi-arid steppe in Inner Mongolia,China

Steppe ecosystems are regarded as an important sink of atmospheric methane (CH₄) and grazing is hypothesized to reduce CH₄ uptake. However, firm experimental evidence is required to prove this hypothesis. Using a fully automated, chamber-based measuring system, we conducted continuous high-frequency (at a 3-h interval) measurements of CH₄ uptake in a Leymus chinensis steppe, which is a typical grassland ecosystem in Inner Mongolia, China. Two management regimes were investigated: ungrazed since 1999 (UG99) and winter-grazed since 2001 (WG01). Measurements were carried out continuously during the periods of June–September 2004, May–September 2005 and March–June 2006. During all of these periods, significantly lower mean CH₄ uptake (±S.E.) at WG01 (28±0.7 μg C m⁻² h⁻¹) as compared to UG99 (56±1.0 μg C m⁻² h⁻¹) (p<0.01) was found. Total CH₄ uptake during the growing seasons (May–September) 2004 and 2005 at WG01 and UG99 was quantified as 1.15 and 2.15 kg C ha⁻¹, respectively. Annual rates of CH₄ uptake were approximately 1.91 (WG01) and 3.58 kg C ha⁻¹ (UG99), respectively. These results indicate that winter-grazing of steppe significantly reduced atmospheric CH₄ uptake by ca. 47%. The winter-grazing practice may have inhibited CH₄ uptake by (a) increasing the likelihood of physiological water stress for CH₄-consuming bacteria during dry periods, (b) decreasing gas diffusion into the soil and, (c) reducing the populations of CH₄ oxidizing bacteria. These three mechanisms could have collectively or independently facilitated the observed inhibitory effects. Our results suggest that grazing exerts a considerable negative impact on CH₄ uptake in semi-arid steppes at regional scales. Notwithstanding, further studies involving year-round, intensive measurements of CH₄ uptake are needed.     

Sulfuric odorous compounds emitted from pig-feeding operations

The objective of the study was to quantify the concentration and emission levels of sulfuric odorous compounds emitted from pig-feeding operations. Five types of pig-housing rooms were studied: gestation, farrowing, nursery, growing and fattening rooms. The concentration range of sulfuric odorous compounds in these pig-housing rooms were 30–200 ppb for hydrogen sulfide (H₂S), 2.5–20 ppb for methyl mercaptan (CH₃SH), 1.5–12 ppb for dimethyl sulfide (DMS; CH₃SCH₃) and 0.5–7 ppb for dimethyl disulfide (DMDS; CH₃S₂CH₃), respectively. The emission rates of H₂S, CH₃SH, DMS and DMDS were estimated by multiplying the average concentration (mg m⁻³) measured near the air outlet by the mean ventilation rate (m³ h⁻¹) and expressed either per area (mg m⁻² h⁻¹) or animal unit (AU; liveweight of the pig, 500 kg) (mg pig⁻¹ h⁻¹). As a result, the emission rates of H₂S, CH₃SH, DMS and DMDS in the pig-housing rooms were 14–64, 0.8–7.3, 0.4–3.4 and 0.2–1.9 mg m⁻² h⁻¹, respectively, based on pig's activity space and 310–723, 18–80, 9–39 and 5–22 mg AU⁻¹ h⁻¹, respectively, based on pig's liveweight, which indicates that their emission rates were similar, whether based upon the pig's activity space or liveweight. In conclusion, the concentrations and emission rates of H₂S were highest in the fattening room followed by the growing, nursery, farrowing and gestation rooms whereas those of CH₃SH, DMS and DMDS concentrations were largest in the growing room followed by the nursery, gestation and farrowing rooms.     

Natural and anthropogenic methane sources in New England

We have recently completed a methane emissions inventory for the New England region. Methane emissions were calculated to be 0.91 Tg yr^-1, with wetlands and landfills dominating all other sources. Wetlands are estimated to produce 0.33 Tg CH₄ yr^-1, of which 74% come from Maine. Active landfills emit an estimated 0.28 Tg CH₄ yr^-1, 60% of which are generated from twelve landfills. Although uncertainty in the estimate is greater, emissions from closed landfills are on the same order of magnitude as active landfills and wetlands; 0.25 Tg CH₄ yr^-1. Sources of moderate magnitude include ruminant animals (0.05 Tg CH₄ yr^-1) and residential wood combustion (0.03 Tg CH₄ yr^-1). Motor vehicles, natural gas, and wastewater treatment make only minor contributions. New England is heavily forested and the soil uptake of atmospheric methane in upland forests, 0.06 Tg CH₄ yr^-1, decreases emissions from soils by about 18%. Although uncertainties remain, our estimates indicate that even in a highly urbanized region such as New England, natural sources of methane make the single greatest contribution to total emissions, with state totals varying between 8% (Massachusetts) and 92% (Maine). Because emissions from only a few large landfills dominate anthropogenic sources, mitigation strategies focused on these discrete point sources should result in significant improvements in regional air quality. Current federal regulations mandate landfill gas collection at only the largest sites. Expanding recovery efforts to moderately sized landfills through either voluntary compliance or further regulations offers the best opportunity to substantially reduce atmospheric methane in New England. In the short term, however, the large contribution from closed, poorly regulated landfills may make the attribution of air quality improvements difficult. Mitigation efforts toward these landfills should also be a priority.     

The composition and sources of PM2.5 organic aerosol in two urban areas of Chile

Fine particle (PM_2.5) samples were collected, using a charcoal diffusion denuder, in two urban areas of Chile, Santiago and Temuco, during the winter and spring season of 1998. Molecular markers of the organic aerosol were determined using GC/MS. Diagnostic ratios and molecular tracers were used to investigate the origin of carbonaceous aerosols. As main sources, road and non-road engine emissions in Santiago, and wood burning in Temuco were identified. Cluster analysis was used to compare the chemical characteristics of carbonaceous aerosols between the two urban environments. Distinct differences between Santiago and Temuco samples were observed. High concentrations of isoprenoid (30–69 ng m⁻³) and unresolved complex mixture (UCM) of hydrocarbons (839–1369 ng m⁻³) were found in Santiago. High concentrations of polynuclear aromatic hydrocarbons (751±304 ng m⁻³) and their oxygenated derivatives (4±2 ng m⁻³), and of n-alk-1-enes (16±13 ng m⁻³) were observed in Temuco.     

Atmospheric degradation of fluoroesters (FESs): Gas-phase reactivity study towards OH radicals at 298 K

Using the relative technique, rate coefficients have been measured for the gas phase reactions of hydroxyl radicals with four fluoroacetates, methyl trifluoroacetate (CF₃COOCH₃), ethyl trifluoroacetate (CF₃COOCH₂CH₃), methyl difluoroacetate (CF₂HCOOCH₃) and 2,2,2-trifluoroethyl trifluoroacetate (CF₃COOCH₂CF₃). Experiments were carried out at 296±2 K and atmospheric pressure (∼750 Torr) using nitrogen or synthetic air as bath gases. The following rate coefficients were derived for the reaction of OH radicals (in units of cm³ mol⁻¹ s⁻¹) with CF₃COOCH₃, k=(4.97±1.04)×10⁻¹⁴, CF₃COOCH₂CH₃, k=(2.64±0.59)×10⁻¹³, CF₂HCOOCH₃, k=(1.48±0.34)×10⁻¹³ and CF₃COOCH₂CF₃, (1.05±0.23)×10⁻¹³. The rate constants obtained are compared with previous literature data of other volatile organic compounds to establish reactivity trends. Atmospheric implications are discussed in terms of lifetimes and fates of the fluoroacetates in the troposphere.     

Characterization of emissions from portable household combustion devices: particle size distributions,emission rates and factors,and potential exposures

A series of source tests were conducted to characterize emissions of particulate matter (PM), carbon monoxide (CO), carbon dioxide (CO₂), methane (CH₄), and total hydrocarbon (THC ) from five types of portable combustion devices. Tested combustion devices included a kerosene lamp, an oil lamp, a kerosene space heater, a portable gas range, and four unscented candles. All tests were conducted either in a well-mixed chamber or a well-mixed room, which enables us to determine emission rates and emission factors using a single-compartment mass balance model. Particle mass concentrations and number concentrations were measured using a nephelometric particle monitor and an eight-channel optical particle counter, respectively. Real-time CO concentrations were measured with an electrochemical sensor CO monitor. CO₂, CH₄, and THC were measured using a GC-FID technique. The results indicate that all particles emitted during steady burning in each of the tested devices were smaller than 1.0 μm in diameter with the vast majority in the range between 0.1 and 0.3 μm. The PM mass emission rates and emission factors for the tested devices ranged from 5.6±0.1 to 142.3±40.8 mg h⁻¹ and from 0.35±0.06 to 9.04±4.0 mg g⁻¹, respectively. The CO emission rates and emission factors ranged from 4.7±3.0 to 226.7±100 mg h⁻¹ and from 0.25±0.12 to 1.56±0.7 mg g⁻¹, respectively. The CO₂ emission rates and emission factors ranged from 5500±700 to 210,000±90,000 mg h⁻¹ and from 387±45 to 1689±640 mg g⁻¹, respectively. The contributions of CH₄ and THC to emission inventories are expected to be insignificant due both to the small emission factors and to the relatively small quantity of fuel consumed by these portable devices. An exposure scenario analysis indicates that every-day use of the kerosene lamp in a village house can generate fine PM exposures easily exceeding the US promulgated NAAQS for PM_2.5.     

Response of methane emission to invasion of Spartina alterniflora and exogenous N deposition in the coastal salt marsh

Spartina alterniflora exhibits great invading potential in the coastal marsh ecosystems. Also, nitrogen (N) deposition shows an apparent increase in the east of China. To evaluate CH₄ emissions in the coastal marsh as affected by the invasion of S. alterniflora and N deposition, we measured CH₄ emission from brackish marsh mesocosms vegetated with S. alterniflora and a native plant, Suaeda salsa, and fertilized with exogenous N at the rates of 0 and 2.7 g N m^?2, respectively. Dissolved porewater CH₄ concentration and redox potentials in soils as well as aboveground biomass and stem density of plants were also monitored. The averaged rate of CH₄ emission during the growing season in the S. alterniflora and S. salsa mesocosms without N application was 0.88 and 0.54 mg CH₄ m^?2 h^?1, respectively, suggesting that S. alterniflora plants significantly increased CH₄ emission mainly because of higher plant biomass rather than stem density compared to S. salsa, which delivered more substrates to the soil for methanogenesis. Exogenous N input dramatically stimulated CH₄ emission by 71.7% in the S. alterniflora mesocosm. This increase was attributable to enhancement in biomass and particularly stem density of S. alterniflora driven by N application, which transported greater photosynthesis products than oxygen into soils for CH₄ production and provided more pathways for CH₄ emission. In contrast, there was no significant effect of N fertilization on CH₄ emission in the S. salsa mesocosm. Although N fertilization significantly stimulated CH₄ production by increasing S. salsa biomass, no significant increase in stem density was observed. This fact, along with the low gas transport capacity of S. salsa, failed to efficiently transport CH₄ from wetlands into the atmosphere. Thus we argue that the stimulatory or inhibitory effect of N fertilization on CH₄ emission from wetlands might depend on the gas transport capacity of plants and their relative contribution to substrates for CH₄ production and oxygen for CH₄ oxidation in soil.     

Impact of permanent inundation on methane emissions from a Spartina alterniflora coastal salt marsh

To understand the effect of water level on CH₄ emissions from an invasive Spartina alterniflora coastal brackish marsh, we measured CH₄ emissions from intermittently and permanently (5 cm water depth) inundated mesocosms with or without N fertilizer added at a rate of 2.7 g N m^?2. Dissolved CH₄ concentrations in porewater and vertically-profiled sediment redox potential were measured, as were aboveground biomass and stem density of S. alterniflora. Mean CH₄ fluxes during the growing season in permanently inundated mesocosms without and with N fertilizer were 1.03 and 1.73 mg CH₄ m^?2 h^?1, respectively, which were significantly higher than in the intermittently inundated mesocosms. This response indicates that prolonged submergence of sediment, up to a water depth of 5 cm, stimulated CH₄ release. Inundation did not greatly affect aboveground biomass and stem density, but did significantly reduce redox potential in sediment, which in turn stimulated CH₄ production and increased the CH₄ concentration of porewater, resulting in higher CH₄ emission in the mesocosm. Our data showed that the stimulatory effect of shallow, permanent inundation on CH₄ emission in S. alterniflora marsh sediment was due primarily to an improved methanogenic environment rather than an increase in plant-derived substrates and/or the number of gas emission pathways through the plant’s aerenchymal system.