Sources Of Non-methane Hydrocarbons Research Articles

Source apportionment of ambient non-methane hydrocarbons in Hong Kong: Application of a principal component analysis/absolute principal component scores (PCA/APCS) receptor model

Receptor-oriented source apportionment models are often used to identify sources of ambient air pollutants and to estimate source contributions to air pollutant concentrations. In this study, a PCA/APCS model was applied to the data on non-methane hydrocarbons (NMHCs) measured from January to December 2001 at two sampling sites: Tsuen Wan (TW) and Central & Western (CW) Toxic Air Pollutants Monitoring Stations in Hong Kong. This multivariate method enables the identification of major air pollution sources along with the quantitative apportionment of each source to pollutant species. The PCA analysis identified four major pollution sources at TW site and five major sources at CW site. The extracted pollution sources included vehicular internal engine combustion with unburned fuel emissions, use of solvent particularly paints, liquefied petroleum gas (LPG) or natural gas leakage, and industrial, commercial and domestic sources such as solvents, decoration, fuel combustion, chemical factories and power plants. The results of APCS receptor model indicated that 39% and 48% of the total NMHCs mass concentrations measured at CW and TW were originated from vehicle emissions, respectively. 32% and 36.4% of the total NMHCs were emitted from the use of solvent and 11% and 19.4% were apportioned to the LPG or natural gas leakage, respectively. 5.2% and 9% of the total NMHCs mass concentrations were attributed to other industrial, commercial and domestic sources, respectively. It was also found that vehicle emissions and LPG or natural gas leakage were the main sources of C 3–C 5 alkanes and C 3–C 5 alkenes while aromatics were predominantly released from paints. Comparison of source contributions to ambient NMHCs at the two sites indicated that the contribution of LPG or natural gas at CW site was almost twice that at TW site. High correlation coefficients (R 2 > 0.8) between the measured and predicted values suggested that the PCA/APCS model was applicable for estimation of sources of NMHCs in ambient air.

Ground-Based and Airborne Measurements of Nonmethane Hydrocarbons in BERLIOZ: Analysis and Selected Results

During the Berlin Ozone Experiment BERLIOZ in July–August 1998 quasi-continuous measurements ofC2–C12 nonmethane hydrocarbons (NMHCs) were carried out at 10 sites in and around the city of Berlin using on-line gas-chromatographic systems (GCs) with a temporal resolution of 20–120 minutes. Additional airborne NMHCmeasurements were made using canister sampling on three aircraft and an on-line GC system on a fourth aircraft. The ground based data are analyzed to characterize the different sites and to identify the influence of emissions from Berlin on its surroundings. Benzene mixing ratios at the 4 rural sites were rather low (<0.5 ppbv). Berlin (and the surrounding highway ring) was identified as the main source of anthropogenic NMHCs at Eichstadt and Blossin, whilst other sources were important at the furthermost site Menz. The median toluene/benzene concentration ratio in Berlin was 2.3 ppbv/ppbv, agreeing well with measurements in other German cities. As expected, the ratios at the background sites decreased with increasing distance to Berlin and were usually around one or below. On 20 and 21 July, the three northwesterly sites were situated downwind of Berlin and thus were influenced by its emissions. Considering the distance between the sites and the windspeed, the city plume was observed at reasonable time scales, showing decreasing toluene/benzene ratios of 2.3, 1.6 and 1.3 with increasing distance from Berlin. Isoprene was the only biogenic NMHC measured at BERLIOZ. It was themost abundant compound at the background sites on the hotter days, dominating the local NMHC reactivity with averaged contributions to the total OH loss rate of 51% and 70% at Pabstthum and Blossin, respectively. Emissionratios (relative to CO and to the sum of analysed NMHCs) were derived from airborne measurements. The comparison with an emission inventory suggests traffic-related emissions to be the predominating source of the considered hydrocarbon species. Problems were identified with the emission inventory for propane, ethene and pentanes.

Analysis of motor vehicle emissions during the Nashville/Middle Tennessee Ozone Study

On‐road gasoline and diesel‐powered vehicle emissions in Nashville, Tennessee, were characterized using fuel sales as a measure of vehicle activity, and emission factors derived from infrared remote sensing, ambient air concentration ratios, and roadway tunnel measurements. On‐road vehicle emissions of carbon monoxide (CO), nonmethane hydrocarbons (NMHC), and oxides of nitrogen (NOx) on weekdays during summer 1995 were estimated to be 270±60, 43±13, and 53±9 metric tons per day, respectively. Diesel engines were a minor source of CO and NMHC, but were responsible for ∼50% of NOx emissions from on‐road vehicles. The Environmental Protection Agency's MOBILE 5B emission model predictions were similar to fuel‐based estimates for all pollutants, except for NOx where the MOBILE model predicted a smaller contribution to total on‐road vehicle emissions from diesel engines. Chemical composition profiles for hydrocarbon emissions were developed based on tunnel air and fuel samples collected in Nashville during summers 1995 and 1999. More than half of the tunnel NMHC mass was liquid fuel that escaped combustion; the remaining mass came from products of incomplete combustion such as ethane, acetylene, C2‐C4 alkenes, and 1,3‐butadiene. No major changes in the composition of vehicle‐related NMHC emissions were observed between 1995 and 1999 in Nashville.

Hydrocarbon source apportionment in Mexico City using the chemical mass balance receptor model

A field study was conducted in Mexico City during May–November 1997 to determine non-methane hydrocarbons (NMHC) species emitted from different sources: application of slow curing asphalt pavement, liquefied petroleum gas (vapour phase), dry cleaning, graphic arts, landfill, emissions of motor vehicle exhaust inside a tunnel, hot soak, whole gasoline, painting operations and degreasing. Forty-five ambient air samples of NMHC were simultaneously collected from 6:00 to 9:00 a.m. at three different sites, Xalostoc, Pedregal and La Merced, denominated receptors, during the spring and fall of 1996. In both cases samples were collected in stainless-steel canisters and analysed by gas chromatography with flame ionisation detection system. Based on these measurements the chemical mass receptor model (CMB) was applied to estimate the contribution of the different NMHC source to ambient pollution. The average results for the two sampling periods showed that the major sources of NMHC for the three sites were: motor vehicle exhaust with an average contribution of 54.9, 57.4 and 63.8% for Xalostoc, Pedregal and La Merced, respectively, followed by handling and distribution of liquefied petroleum gas with 28.5% in Xalostoc, 20.0% in Pedregal and 24.0% in La Merced.

Nonmethane hydrocarbons in the troposphere: Impact on the odd hydrogen and odd nitrogen chemistry

The chemistry of light nonmethane hydrocarbons (NMHCs), including C2H6, C3H8, n‐C4H10, C2H4, and C3H6, was incorporated into a seasonally varying, one‐dimensional model of the mid‐latitude troposphere (45°N). Simulations were performed for both marine and continental atmospheres. Where possible, these simulations have been compared with surface and aircraft measurements of test molecules, such as C2H6, C3H8, CO, peroxyacetyl nitrate (PAN), and peroxypropionyl nitrate (PPN). Model calculations predict that NMHC oxidation produces acetaldehyde and acetone in concentrations that can exceed that of formaldehyde. Organic peroxides were found to be present in concentrations that, considered collectively, are comparable to that of hydrogen peroxide. Peroxyacetyl nitrate is the dominant odd nitrogen (NOx) compound in wintertime and is surpassed only by HNO3 during the summer. The inclusion of NMHC‐PAN chemistry has little effect on summertime odd hydrogen/odd nitrogen photochemistry, but is shown to have a substantial impact in wintertime, particularly over the continents, where NOx concentrations are high and temperatures are low. Under these circumstances, oxidation of NMHC compounds can enhance ground‐level OH and HO2 concentrations by factors of 5–50, respectively. Formation of PAN during the wintertime can reduce upper tropospheric NOx concentrations by a factor of 2–3 over the oceans and a factor of 20–30 over the continents. Significant changes also occur in the predicted concentrations of HNO3 and HO2NO2. The effects of NMHCs on wintertime photochemistry might be moderated by seasonal variations in NMHC source strengths or by horizontal transport of trace gases from the continents to the oceans and from high latitudes toward the equator. Nonetheless, it seems likely that models of the troposphere must include NMHC‐PAN chemistry in order to correctly predict the seasonal behavior of trace chemicals.

Authors' reply

The concentration, composition, and variability of nonmethane hydrocarbons (NMHCs) and carbon monoxide (CO) were characterized in a suburban region of south-central China. Weekly samples were collected in 2007 in the Changsha suburban area and analyzed with a three-stage preconcentration method coupled with GC–MS. A time series of NMHC measurements showed seasonal variation, with a higher level occurring in winter and a lower level in summer. Toluene was the most abundant species with an average concentration of 2.51 ± 1.87 ppbv, followed by benzene (2.04 ± 1.30 pptv). According to the level of identified NMHCs, vehicular exhaust appears to be the main source of NMHCs in Changsha. Among alkanes, the highest level is propane with a concentration of 1.31 ± 0.71 ppbv, it indicated an extensive use and leakage of liquefied petroleum gas (LPG) in Changsha. The concentrations of NMHCs were influenced by the wind direction; a high level of NMHCs was carried by winds from southern China. Significant biogenic isoprene emissions were observed, with good correlation between isoprene level and temperature. Finally, when the typical individual NMHC species and CO in the morning and afternoon were compared, the shorter lifetime of NMHC species relative to CO could explain the poorer correlation observed in the afternoon.