Total Non-methane Hydrocarbons Research Articles

Biogenic hydrocarbon emissions and landcover/climate change in a subtropical savanna

Biogenic non-methane hydrocarbon (NMHC) emissions strongly influence the chemical composition of the troposphere. Thus, variations in emissions of these compounds are expected to cause changes in concentrations of important atmospheric trace gases. Here, we assess the relative magnitude of potential changes in NMHC (e.g., isoprene and monoterpene) emissions using field flux measurements from a subtropical savanna parkland/thorn woodland site in conjunction with model predictions of climate and landcover change. NMHC emissions of about 40 plant species were characterized. Grasses, as a group, had low emission rates. Several common woody species had high emission rates. However, there was little evidence of emissions being consistently related to woody plant taxonomy, growthform or functional groups. Above-canopy measurements were used to validate modeled isoprene flux predictions of about 2 mg C m−2 h−1 for savanna parkland/thorn woodland and ca. 0.7 mg C m−2 h−1 for the regional landscape, which is a mixture of savanna parkland/thorn woodland and cropland. Linkage of the biogenic emissions model with a plant succession model indicated that landcover change since the early 1800s has elicited a 3-fold increase in total NMHC emissions. This increase reflected changes in vegetation species composition (from domination by grasses which were typically ‘low emitters’, to shrubs and trees, many of which were ‘high emitters’) and increases in foliar density. Field measurements on two common shrub species indicated that isoprene emission increased exponentially with increases in leaf temperature from 20 to 40° C and were not suppressed by drought stress. Accordingly, our model predicted that projected increases in ambient temperature (3 to 6°C) emissions could produce a 2-fold increase in biogenic NMHC emissions. Cloud cover, precipitation, relative humidity, and winds also exerted some control over NMHC emissions, but their influence was highly variable and difficult to estimate. Although our results are specific to southern Texas USA, they indicate the magnitude of change in NMHC emissions that could occur at other locations when climate and vegetation composition are altered.

Crown fire emissions of CO2, CO, H2, CH4, and TNMHC from a dense Jack pine boreal forest fire

Samples of high‐intensity crown fire smoke were collected using a helicopter during the International Crown Fire Modeling Experiment near Fort Providence, Northwest Territories, Canada. The samples were analyzed for carbon dioxide (CO2), carbon monoxide (CO), hydrogen (H2), methane (CH4), and total nonmethane hydrocarbons (TNMHC). CO2− normalized mean emission ratios (ERs) and emission factors (g product/kg fuel burned) were determined for CO2, CO, H2, CH4, and TNMHC. Carbon monoxide production was determined to increase during high‐intensity crowning. Unlike CO, a corresponding increase in the production of H2, CH4, and TNMHC during crowning was not detected. This represents the first clear indication that we know of where relative increases in CO production from vegetation fires are not positively correlated with corresponding increases in CH4, H2, and TNMHC production. These results may be important to the atmospheric carbon budget, and to the potential use of CO as a normalizing parameter for boreal forest fire emissions.

Hazardous air pollutant and ozone precursor emissions from a low-NO x natural gas-fired industrial burner

Due to heightened environmental concerns, urban areas throughout the world are switching to natural gas for fueling continuous stationary combustion systems. As natural gas systems shift to lean, premixed operation to reduce NO x formation and maintain high combustion efficiency, hazardous air pollutant and ozone precursor emissions—specifically, volatile organic compounds (VOCs)—may potentially increase. The regulation of stationary source VOC pollutants under the 1990 Clean Air Act Amendments may pose unforeseen challenges in the design and operation of advanced gas-fired combustion systems. The present paper investigates the relationship between VOC emissions and excess air, fuel-air mixing, and NO x and CO emission levels for a scaled, generic, low-NO x , natural gas-fired burner. The stack samples were analyzed for C 2 −C 10 aliphatic hydrocarbons, aromatic hydrocarbons, and aldehydes. Most VOCs were emitted in low concentrations (<100 ppbv). However, certain conditions or high swirl ability limits generated relatively high total VOC levels (≈.01–10 ppmC). The VOC concentrations correlated well with CO and total nonmethane hydrocarbon values, indicating that these two parameters may serve as surrogates for VOC emissions under lean conditions. The results suggest that there are selected optimal operating conditions that minimize all pollutants. If natural gas-fired systems operate at their optimal conditions, a significant regulatory concern with respect to hazardous air pollutant and ozone precursor emissions can be mitigated.

Characterization of non-methane hydrocarbons in the rural southeast United States

Measurements of non-methane hydrocarbons, as well as ozone, meteorological and trace gas data, made at four rural sites located within the southeastern United States as a part of the Southern Oxidants Study are compared. The C 2–C 10 hydrocarbons were obtained during the 1200–1300 local time period, once every six days from September 1992 through October 1993. The light molecular weight alkanes (ethane, propane, n-butane, iso-butane, ethene and acetylene) display a seasonal variation of a winter maximum and summer minimum. Isoprene was virtually non-existent during the winter at all sites, and averaged from 9.8 ppbC (Yorkville, Georgia) to 21.15 ppbC (Centreville, Alabama) during the summer. The C 10 terpene concentration was largest during the summer period with averages ranging between 3.19 ppbC (Centreville, Alabama) and 6.38 ppbC (Oak Grove, Mississippi); winter time concentrations ranged from 1.25 to 1.9 ppbC for all sites. Propylene-equivalent concentrations were calculated to account for differences in reaction rates between the hydroxyl radical and individual hydrocarbons, and to thereby estimate their relative contribution to ozone, especially in regard to the highly reactive biogenic compounds such as isoprene. The propy-equivalent concentrations from the biogenics represent at least 65% of the total non-methane hydrocarbon sum at these four sites during the summer season. A plot of ozone versus NO γ-NO highlights the NO x limited relationship of this region.

A global three‐dimensional chemical transport model: 2. Nitrogen oxides and nonmethane hydrocarbon results

In this paper, nitrogen oxide and total nonmethane hydrocarbons (NMHCs) from the University of Oslo global three‐dimensional chemical transport model (CTM) are presented and compared with data from both surface and free tropospheric observations. The model includes the most important processes, including photochemical and thermal reactions, wet and dry deposition, natural and anthropogenic emissions, stratospheric contributions of NOy, and daily variations in the meteorological fields generated from the NASA Goddard Institute for Space Studies general circulation model. The model exhibits daily and seasonal variations in NMHC and NOy species, consistent with our understanding of tropospheric photochemistry. Generally good agreement between modeled mixing ratios and observations is shown for NOy, PAN and total NMHCs over 3 orders of magnitude in both source and reote regions. For NOx, the model gives good agreement in rural and urban regions; however it tends to under predict clean free tropospheric concentrations by about 20 parts per trillion by volume (50–100%). This is most likely due to subgrid boundary layer exchange processes, too efficient removal of NOx and/or recent increases in NOx emissions which are not included in our 1980 emissions inventory (especially in east Asia). Seasonal cycles for NOx, PAN, NOy and NMHCs from a number of surface locations where these data are available are reproduced well. Speciation of NOy in the model is shown to be consistent with observations at three sites where such data are available; Scotia, Pennsylvania; Mauna Loa, Hawaii; and Alert, Northwest Territories where different NOy species dominate at each location (NOx, HNO3, and PAN respectively). Several uses of the CTM are demonstrated. Total tropospheric NOx, PAN5 HNO3, and NOy are calculated with the model and shown to vary seasonally. The seasonal variations are consistent with enhanced lifetimes during winter. The model is also used to determine the fractional contributions of NOy from the major anthropogenic source regions (Europe, Asia, and North America) at Mauna Loa. Future applications of the model will focus on the global ozone and nitrogen budgets and the sources of NOx to the remote free troposphere.

NOx during ozone depletion events in the arctic troposphere at Ny-Ålesund, Svalbard

Measurements of NOx, ozone, non-methane hydrocarbons (NMHC), and other atmospheric constituents were made at the Zeppelin-mountain atmospheric monitoring station near Ny-Ålesund, Svalbard, during the spring of 1994. On a few occasions, we observed tropospheric ozone depletion events with minimum ozone mixing ratios of 3.9 ppbv that lasted for up to 2 days. This paper presents the first measurements of NOx during ozone depletion events. The objective of this work is to explore the role of NOx during those periods. During depletion periods, mixing ratios of NOx, total NMHC, and acetylene dropped to minima of < 4.5 pptv, 3.6 ppbCv, and 123 pptv, respectively. These mixing ratios were significantly lower than the means for our campaign, which were 23.6 pptv, 14.3 ppbCv, and 478 pptv, respectively. Because NO2 would quickly scavenge the BrO radical, the low observed NOx mixing ratios are consistent with proposed mechanisms involving catalytic destruction of ozone by the Br radical. A mechanism involving NOx to recycle halogen radicals seems unlikely in light of the current study.

Source compositions of trace gases released during African savanna fires

Measurements of biomass burn‐produced trace gases were made using low‐altitude helicopter penetrations of smoke plumes above burning African savanna during the Southern African Fire‐Atmosphere Research Initiative (SAFARI‐92). Smoke from two large prescribed fires conducted in the Kruger National Park, South Africa, on September 18 and 24, 1992, was sampled at altitudes ranging from 20 to 100 m above ground level during flaming and smoldering phases of combustion. Carbon dioxide (CO2) normalized emission ratios (dX/dCO2 (vol/vol), where X denotes a trace gas) for carbon monoxide (CO), hydrogen (H2), methane (CH4), total nonmethane hydrocarbons (TNMHC), and nitrous oxide (N2O) were determined. The emission ratios were used in conjunction with fuel consumption estimates to calculate emission factors (grams of product per gram of fuel) for these gases. Emission factors for CO2, CO, CH4, and N2O of 1.61, 0.055, 0.003, and 1.6 × 10−4 g/g fuel, respectively, were determined. The fires advanced rapidly through the savanna (primarily grass) fuels with minimal amounts of smoldering combustion. The relatively low emission ratios determined for these fires indicated excellent combustion efficiency. About 93% of the carbon released into the atmosphere as a result of these fires was in the form of CO2.

Volatile organic compounds up to C 20 emitted from motor vehicles; measurement methods

To understand better the sources of observed differences between on-road vehicle emissions and model estimates, and to evaluate the emission of ozone precursors from motor vehicles, a series of experiments was conducted in the Fort McHenry Tunnel, Baltimore, Maryland (18–24 June 1992), and in the Tuscarora Mountain Tunnel, Pennsylvania (2–8 September 1992). Samples were collected using stainless steel canisters (whole air samples, analyzed for C 2C 12 hydrocarbons), Tenax-TA solid adsorbent cartridges (for semi-volatile hydrocarbons, in the C 8C 20 range), and 2,4-dinitrophenylhydrazine (DNPH) impregnated cartridges (for carbonyl compounds). The samples were analyzed using high resolution gas chromatographic separation with Fourier transform infrared/mass spectrometric detection (GC/IRD/ MSD) for qualitative identification and with flame ionization detection (GC/FID) for quantitation of hydrocarbons, and high performance liquid chromatography (HPLC) for identification and quantitation of carbonyl compounds. A custom-designed database management system was used to handle the large data sets generated by these analyses. From the evaluation of canister and Tenax sample stability upon storage, it was found that hydrocarbons in the C 8C 12 range seemed to be more stable in the Tenax cartridge than in the canister. The effect of the Nafion® dryer (frequently used for moisture removal prior to cryogenic concentration of the canister samples) was also assessed and it was found to lower the measured concentrations of hydrocarbons collected in the canisters. Comparison of hydrocarbon concentrations found in the Tenax and canister samples allows an assessment of the contribution of semi-volatile hydrocarbons (C 10C 20 range derived from Tenax data) to the total non-methane hydrocarbons (C 2C 20, derived from canisters and Tenax data). The results of this study show that hydrocarbons in the range of C 10C 20 are important components of gas-phase hydrocarbons emitted from heavy-duty diesel vehicles (they account for approximately half of the total gas-phase non-methane hydrocarbon emission rates) and hence that solid adsorbent sampling should be used in addition to canister sampling in measurements of motor vehicle emissions.

Measurements of PAN, alkyl nitrates, ozone, and hydrocarbons during spring in interior Alaska

Measurements of the atmospheric mixing ratios of ozone, peroxyacetylnitrate (PAN), hydrocarbons, and alkyl nitrates were made in a boreal forest ecosystem in the interior of Alaska from March 15 to May 14, 1993. During this period the mixing ratios of PAN, alkyl nitrates, and nonmethane hydrocarbons (NMHCs) generally decreased due to the influence of both meteorology and OH removal. Mean mixing ratios of ozone, PAN, C2 ‐ C6 alkyl nitrates, and total C2 ‐ C5 NMHC during southerly flow periods were 24.4 parts per billion (ppbv), 132.1 parts per trillion (pptv ), 34 pptv, and 8.2 ppbCv, respectively. During a short period of northerly flow, mixing ratios of PAN and total NMHC were approximately 2 times the southerly flow mixing ratios. PAN is correlated with ozone, and alkyl nitrates are correlated with alkanes. PAN and ozone mixing ratios exhibit similar diurnal variations on a number of days with an early morning minimum and afternoon maximum. This is likely due to a diurnal cycle in the boundary layer ‐ free troposphere exchange and loss processes in the boundary layer for both O3 and PAN. Higher molecular weight (mw) hydrocarbons and alkyl nitrates are observed to decrease more quickly than the lower mw hydrocarbons, consistent with removal by OH as the primary loss process.

Volatile hydrocarbons from domestic wood burning

The quantitative proportions of 16 alkenes, 5 alkadienes, 5 alkynes and several alkanes and arenes were determined in emissions from wood burning in a wood-stove and in small-scale model experiments. Samples were taken on triple-layer adsorption cartridges, and gas chromatographic separations were performed on an aluminium oxide column. Ethene, ethyne and benzene were major components, especially from efficient flame combustion. The proportions of C 3C 7 alkenes were markedly higher for smouldering. The carcinogenic compounds benzene and 1,3-butadiene constituted roughly 10–20% and 1–2% by weight of total non-methane hydrocarbons. Similar results were obtained for hardwood and softwood.

The composition and concentration of hydrocarbons in the range of C2 to C18 emitted from motor vehicles

Sampling was carried out in the Caldecott Tunnel, located in the San Francisco (California) area. Three daily samples were collected, using stainless steel canisters and Tenax-TA solid adsorbent cartridges, over 2 days in June 1991. The samples were analyzed using high resolution gas chromatographic separation and Fourier transform infrared/mass spectrometric detection (GC/IRD/MSD) or flame ionization detection (FID) of individual hydrocarbons. The comparison of hydrocarbon concentrations found in the Tenax and canister samples and the assessment of the contribution of semivolatile hydrocarbons (C10–C18 range) to total non-methane hydrocarbons (C2–C10), as measured by the canister method, is presented.

Measurements of trace gases emitted by Australian savanna fires during the 1990 dry season

During 18–23 July 1990, 31 smoke samples were collected from an aircraft flying at low altitudes through the plumes of tropical savanna fires in the Northern Territory, Australia. The excess (above background) mixing ratios of 17 different trace gases including CO2, CO, CH4, several non-methane hydrocarbons (NMHC), CH3CHO, NO x (− NO + NO2), NH3, N2O, HCN and total unspeciated NMHC and sulphur were measured. Emissionratios relative to excess CO2 and CO, and emissionfactors relative to the fuel carbon, nitrogen or sulphur content are determined for each measured species. The emission ratios and factors determined here for carbon-based gases, NO x , and N2O are in good agreement with those reported from other biomass burning studies. The ammonia data represent the first such measurements from savanna fires, and indicate that NH3 emissions are more than half the strength of NO x emissions. The emissions of NO x , NH3, N2O and HCN together represent only 27% of the volatilised fuel N, and are primarily NO x (16%) and NH3 (9%). Similarly, only 56% of the volatilised fuel S is accounted for by our measurements of total unspeciated sulphur.

In situ nonmethane hydrocarbon measurements on SAGA 3

During the third Soviet‐American Gas and Aerosol (SAGA 3) expedition to the central Pacific in February to March 1990 we observed C1‐C5 nonmethane hydrocarbons (NMHCs) both in the atmosphere and in the ocean. Atmospheric NMHCs project strongly on two factors: those NMHCs with lifetimes over 1 week (ethane, ethyne, propane, cyclopropane) display north‐south latitudinal gradients whose magnitudes are proportional to their photochemical loss rates, which is consistent with a northern hemispheric, continental source, while those NMHCs with lifetimes under 1 week (all alkenes and pentane) do not display latitudinal gradients but do vary in common in a more complicated manner, consistent with a heterogeneous, marine source. Data taken from a sea water equilibrator shows that alkene concentrations vary strongly with wind speed, supporting previous conclusions that sea‐air evasion is a major loss term for mixed layer alkenes. A reasonable balance exists between sea‐air fluxes and atmospheric column removal for some alkenes (ethene, propene, 1‐butene, and 1‐pentene), while the remainder are out of balance, with partial pressures insufficient to support atmospheric observations. The total NMHC sea‐air flux is about 0.8 μmole m−2d−1. Both our air and water concentrations fall near the low end of previously observed ranges. It is argued that some previous higher atmospheric observations may reflect systematic problems with canister sampling. During SAGA 3 the role of NMHCs in the remote atmospheric OH budget was secondary though important, accounting (in conjunction with NMHC oxidation products) for 10 to 20% of all OH removal during baseline periods and a substantially larger fraction during episodes of increased NMHC mixing ratios.

Trace gas emissions from tropical biomass fires: Yucatan Peninsula, Mexico

Mixing ratios for carbon dioxide (CO 2), carbon monoxide (CO), hydrogen (H 2), methane (CH 4) and total non-methane hydrocarbons (TNMHC) were determined from the smoke plumes of two small (∼0.25 ha) prescribed biomass fires conducted on the Yucatan Peninsula in Mexico. In the region of these fires the combination of climate and shallow soils produces a scrubby and stunted forest with species composition similar to the Brazilian rain forest, but at a noticeably reduced size. Aircraft collections of smoke from these fires were analysed and used to determine CO 2-normalized emission ratios ( ΔX/ ΔCO 2; v/v; where Δ = in-plume specie concentration less background concentration) for CO, H 2, CH 4 and TNMHC produced and released into the atmosphere from these fires. Suprisingly, high mean emission ratios for TNMHCs (∼1.7% of CO 2 release) and H 2 (∼2.5% of CO 2) were determined. Emission ratios for CO (∼7%) and CH 4 (∼0.7%), however, were found to fall within expected bounds.

Source Fingerprints for Volatile Non-Methane Hydrocarbons

Non-methane hydrocarbon (NMHC) source profiles consisting of 35 hydrocarbon species were measured for vehicle and petroleum refinery emissions. Refueling emissions were found to be sensitive to the grade and volatility class of fuel and to be composed mainly of saturated hydrocarbons such as n-butane and 2-methy I butane. Unsaturated and aromatic hydrocarbons, which are released from the tailpipe of vehicles as products of combustion and unburned fuel, were more prevalent in roadway emissions comprising approximately 34 percent of the total NMHCs. Cold-start emissions were nearly indistinguishable from the roadway emission profile. The only significant differences were in toluene, ethylene and acetylene, which may be related to the efficiency of combustion when the vehicle is initially started. Saturated hydrocarbon distributions of the hot-soak profiles were found to be similar to refueling emissions. The only significant difference in the profiles was in the aromatic content, which may be related to the grade of the gasoline and the effectiveness of evaporative emission control devices. The temporal variation in refinery emissions was significant and may be related to variations in refinery activities such as the production and blending of feed stocks to produce different fuels.

Trace gas measurements in the Kuwait oil fire smoke plume

We report trace gas measurements made both inside and outside the Kuwait oil‐fire smoke plume during a flight of an instrumented research aircraft on May 30, 1991. Concentrations of SO2, CO, and NOx averaged vertically and horizontally throughout the plume 80 km downwind of Kuwait City were 106, 127, and 9.1 parts per billion by volume (ppbv), respectively, above background concentrations. With the exception of SO2, trace gas concentrations were far below typical U.S. urban levels and primary national ambient air quality standards. Ambient ozone was titrated by NO in the dark, dense core of the smoke plume close to the fires, and photochemical ozone production was limited to the diffuse edge of the plume. Photochemical O3 production was noted throughout the plume at a distance of 160 km downwind of Kuwait City, and averaged 2.3 ppbv per hour during the first 3 hours of transport. Little additional photochemical production was noted at a downwind range of 340 km. The fluxes of sulfur dioxide, carbon monoxide, and reactive nitrogen from the roughly 520 fires still burning on May 30, 1991 are estimated at 1.4 × 107 kg SO2/d, 6.9 × 106 kg CO/d, and 2.7 × 105 kg N/d, respectively. Generally low concentrations of CO and NOx indicate that the combustion was efficient and occurred at low temperatures. Low total nonmethane hydrocarbon concentrations suggest that the volatile components of the petroleum were burned efficiently.

Diurnal HO2 cycles at clean air and urban sites in the troposphere

We have determined HO2 concentrations at two Oregon sites for continuous periods of 36 to 48 hours, using fluorescence assay with gas expansion. At the sea level coastal site (45°N 124°W), NNW winds prevailed during daytime, and a point measurement of very low total nonmethane hydrocarbon concentration indicated the presence of remote tropospheric air of oceanic origin. At the urban site, HO2 was determined during moderately low ozone pollution levels. At both sites, maximum daily [HO2] was in the range of 1–2 × 108 cm−3 under clear‐sky conditions, with an estimated overall uncertainty of 40%. HO2 was detected by continuous low‐pressure sampling with flowing chemical conversion to HO, which was detected by laser‐excited fluorescence. The instrumental response to HO2 was calibrated by the self‐decay of HO2 at atmospheric pressure. Interference in the measured daytime HO2 concentrations by RO2 was estimated at less than 20%.

Factor Analysis of Hydrocarbon Species in the South-Central Coast Air Basin

The composition of canister hydrocarbon data collected at four surface sites and from aircraft during a 1985 field experiment in California's south-central coast air basin was analyzed to determine the source. Statistical routines from a commonly used software package (SAS) were used to perform a principal component extraction on a 15-variable vector space containing the most important hydrocarbons (as well as CO) in the air quality samples. The ratios of each of the 15 hydrocarbon species to total nonmethane hydrocarbon (NMHC) were plotted as a function of the ethane-to-acetylene (E/A) ratio. The plots serve as an estimator of the source profile and were consistent with the source profiles obtained by the principal component analysis. The source reconciliation analysis identified two principal sources. One appears to be rich in acetylene, carbon monoxide (CO), and some unique hydrocarbons. This source corresponds closely to accepted hydrocarbon profiles for automobile emissions. The second major source is high in methane, ethane, and propane, but also contains reasonable amounts of butane and pentane. This type of composition suggests a geogenic source. In addition to these two major sources, clean oceanic air was identified as a third component. The biogenic compound isoprene also occurred in some samples. Canister data from three of four sites were dominated by a profile of trace gases associated with a geogenic source. The reactivity of the geogenic air mass is about 50% that of urban air. The dominance of such a low-reactive emission source affects the amount of ozone predicted by photochemical modeling of the region.

Non-methane hydrocarbon and aldehyde measurements in Budapest, Hungary

Abstract During three summer measuring campaigns the atmospheric concentration of non-methane hydrocarbons and aldehydes were measured at two sites in Budapest. Two hundred and forty-five flask samples were analyzed for non-methane hydrocarbon concentration and hydrocarbon composition. For formaldehyde and acetaldehyde concentration 185 and 122 samples were analyzed, respectively. The total non-methane hydrocarbon concentration shows a characteristic diurnal variation with a peak between 6 a.m. and 9 a.m. At the two sites the average concentrations between 6 a.m. and 9 a.m. are 802 and 606 ppbC, respectively. Comparing the speciation of hydrocarbons in the air of Budapest with that measured in other cities we have realized a relative surplus in C6 alkanes which is balanced by the low contribution of C3–C4 alkanes. Both the formaldehyde and acetyldehyde concentration were found rather high. In the downtown the average concentrations are 10.4 and 4.4 ppb, while 3 km away from the center of the city the corresponding values are 28.0 and 5.8 ppb.

Natural hydrocarbon emissions in the United Kingdom

Natural hydrocarbon emissions from both forests and agricultural lands have been estimated on a regional basis for the U.K. The results of this study suggest total emissions are significantly higher than is currently accepted, with the major forested areas of Scotland, Wales and the north of England dominating the area contributions. Non-methane hydrocarbons (NMHC) emitted from natural sources are estimated at 211 × 10 3 tC yr −1 which represents 13% of the total NMHC emissions in the U.K.