Ambient Non-methane Hydrocarbons Research Articles

Obtaining accurate non-methane hydrocarbon data for ambient air in urban areas: comparison of non-methane hydrocarbon data between indirect and direct methods

Abstract. Since non-methane hydrocarbons (NMHCs) include numerous species of volatile organic compounds (VOCs), they are the only indicators that can characterize the total amount of VOCs in ambient air. More than 90 % of NMHC instruments in the market use the indirect method for NMHC determination, utilizing a gas chromatograph to determine the concentrations of total hydrocarbons (THCs) and methane in air. However, we found indirect NMHC measurements incorrectly characterized the low NMHC concentrations in the urban air. These measurements were hindered by the uncertain changes in the errors associated with low THC concentrations, humidity and macroscopic substances (oxygen) in the atmosphere. In this study, we conducted intercomparisons between 10 instruments in the market using different operation principles; among these, two used the direct method, and eight used the indirect method. For the indirect method, experiments showed that when the NMHC concentration was 50 ppb C, the errors in the measurement results were 32 % (CH4) and 98 % (THC) when compared to theoretical values. The oxygen content in the sample gas directly affected the response of the THC. The effect of increased oxygen content on the analysis of oxygen-containing substances was more significant than that of the increase in hydrocarbon substances. The response of dry zero was blank, and the response value increased non-linearly with relative humidity (RH). RH had a great impact on low NMHC concentrations of nearly 50 %. For the direct method, although various flow designs were applied for different instruments, the results indicated that they generally showed lower interference and higher accuracy for the ambient NMHC measurements. With the online direct methods, we obtained more reliable data and characteristics for low-concentration NMHCs in downtown Shanghai. The median of hourly data was 163.1 ppb C, and the highest ratio of the maximum and minimum concentrations of NMHCs reached 9.56 in a single day.

Long-term field calibration of low-cost metal oxide VOC sensor: Meteorological and interference gas effects

This study aimed to evaluate the performance of the Sensirion SGP30 MOS (metal oxide semiconductor) VOC sensors (SMVSs) for a long sampling period (10–12 months) at different ambient air monitoring stations (AQMSs). In the field tests, temperature (T), relative humidity (RH), carbon monoxide (CO) concentration, and non-methane hydrocarbons (NMHC) concentrations were found to be the crucial parameters influencing the sensor readings. A multiple linear regression (MLR) calibration model using hourly T, RH, CO, and VOC values as parameters was developed at Zhongming (ZM) station and validated at Hsinchu (HC) and Tainan (TN) stations. After calibration, the SMVS performance was improved significantly with the decrease of mean normalized bias (MNBs) and mean normalized errors (MNEs) of hourly-average data from +228 to 473% to ±25.9% and 231–473%–47.2%, respectively based on the reference NMHC values in the AQMSs. For ambient NMHC concentrations higher than 100 ppbv, the MLR-calibrated results were further improved with MNBs (MNEs) less than ±20% (28.3%). The correlation between calibrated sensor data and reference data was enhanced significantly with the R2 values increasing from 0.27 to 0.50 to 0.65–0.78 at three stations. Therefore, these well-calibrated sensors can become viable tools for many purposes including hotspot identification and characterization, and personal exposure study (MNE<30%).

Effects of regional air pollutants on respiratory diseases in the basin metropolitan area of central Taiwan

This study divided a basin metropolitan area with high air pollution into three subareas, namely urban, suburban, and rural, on the basis of population density for a systematic analysis of the effects of local air pollutants on respiratory diseases. A panel data regression model was used to estimate the annual incidence growth rates (AIGRs) of the four respiratory diseases, namely lung cancer, chronic obstructive pulmonary disease, asthma, and pneumonia, resulting from exposure to fine particulate matter (PM2.5, diameter of 2.5 μm or less), odd oxygen (ODO), or nonmethane hydrocarbon (NMHC). The results indicate that the prevailing wind direction is not a major factor determining the distribution of air pollutants. The spatial distributions of ODO and NMHC differed from that of PM2.5. Three air pollutants contributed to positive AIGRs of the four diseases in the study area, but PM2.5 which had a negative AIGR for asthma in the rural subarea. The pollutants with the strongest effects on AIGR, in descending order, were NMHC, PM2.5, and ODO. The effect of ambient NMHC was significant and nonnegligible, especially in the urban subarea. A dimensionless potential AIGR (PAIGR) formula was established to quantitatively compare the effects of different air pollutants on the four respiratory diseases. The results indicate that ambient NMHC had the strongest effect on the incidences of the respiratory diseases, followed by that of ambient PM2.5. The effect of ambient NMHC was significant and nonnegligible, especially in the urban subarea. The PAIGR ratio ranges of PM2.5 to ODO and NMHC to ODO for the four diseases in urban subsarea were from 3 to 19 and from 289 to 920, respectively. This study also applied multivariate regression to assess the association among 5 aspects, namely air quality, point source, line source, area source, and socioeconomic status, and the incidences of the four respiratory diseases. The results indicate that the model has favorable fit and can thus reflect the associations of the 15 factors of 5 aspects with the four respiratory diseases in each subarea.

Long-term ambient hydrocarbon exposure and incidence of urinary bladder cancer

Particulate matter and volatile organic compounds, including total hydrocarbons (THCs), are major ambient air pollutants. Primary nonmethane hydrocarbons (NMHCs) originate from vehicle emissions. The association between air pollution and urinary bladder cancer (UBC) is debatable. We investigated whether long-term exposure to ambient hydrocarbons increases UBC risk among people aged ≥ 20 years in Taiwan. Linkage dataset research with longitudinal design was conducted among 589,135 initially cancer-free individuals during 2000–2013; 12 airborne pollutants were identified. Several Cox models considering potential confounders were employed. The study outcomes were invasive or in situ UBC incidence over time. The targeted pollutant concentration was divided into three tertiles: T1/T2/T3. The mean age of individuals at risk was 42.5 (SD 15.7), and 50.5% of the individuals were men. The mean daily average over 10 years of airborne THC concentration was 2.25 ppm (SD 0.13), and NMHC was 0.29 ppm (SD 0.09). Both pollutants show long-term monotonic downward trend over time using the Mann–Kendall test. There was a dose-dependent increase in UBC at follow-up. UBC incidence per 100,000 enrollees according to T1/T2/T3 exposure to THC was 60.9, 221.2, and 651.8, respectively; it was 170.0/349.5/426.7 per 100,000 enrollees, corresponding to T1/T2/T3 exposure to NMHC, respectively. Without controlling for confounding air pollutants, the adjusted hazard ratio (adj.HR) was 1.83 (95% CI 1.75–1.91) per 0.13-ppm increase in THC; after controlling for PM2.5, adj.HR was even higher at 2.09 (95% CI 1.99–2.19). The adj.HR was 1.37 (95% CI 1.32–1.43) per 0.09-ppm increase in ambient NMHC concentration. After controlling for SO2 and CH4, the adj.HR was 1.10 (95% CI 1.06–1.15). Sensitivity analyses showed that UBC development risk was not sex-specific or influenced by diabetes status. Long-term exposure to THC and NMHC may be a risk factor for UBC development. Acknowledging pollutant sources can inform risk management strategies.

Ambient non-methane hydrocarbons and their contribution to ozone formation potential in a super coal chemical industry in China’s Energy Golden Triangle

Ambient non-methane hydrocarbons (NMHCs) were investigated at Shenhua coal chemical industrial park (SH), and Baofeng coal chemical industrial park (BF) in Ningdong Energy and Chemical Industrial Base (NECIB) in China’s Energy Golden Triangle (EGT). Ambient air samples were collected using pre-evacuated 2-L electro-polished stainless steel canisters at SH and BF from 9:00 a.m. to 9:30 a.m. (UTC+8) from 22 to 31 December 2016. Fifty-seven NMHCs were analyzed using gas chromatography-mass selective detector/flame ionization detector. The average NMHCs mixing ratios were 49.05 ± 44.37 ppbv in SH, and 39.31 ± 18.77 ppbv in BF. Overall, alkanes took up the largest proportion (＞60%), followed by alkenes, acetylene, and aromatics. The propylene-equivalent (Prop-Equiv) concentration and the ozone formation potential (OFP) of NMHCs were calculated to estimate their chemical reactivities. Alkenes played a predominant role in NMHCs reactivity, among which propylene and ethylene were the largest contributors. OFP values show that alkenes and acetylene were the largest contributors (60%) to measured total NMHCs. Ethylene, propylene, m/p-xylene, n-butane, 1-butene, propane and acetylene were the major precursors in ground-level ozone formation in this region, which accounted for 66% and 62% of the total ozone formed by NMHCs at BF and SH, respectively. This study identified that industrial activities were the primary sources of NMHCs, confirmed by the high ratios of benzene to toluene (B/T = 2.23). Therefore, these organic pollutants should be monitored further based on their high toxicities.

Acute effects of ambient non-methane hydrocarbons on cardiorespiratory hospitalizations: A multicity time-series study in Taiwan

BackgroundFew environmental epidemiological studies and no large multicity studies have evaluated the acute short-term health effects of ambient non-methane hydrocarbons (NMHC), the essential precursors of ground-level ozone and secondary organic aerosol formation. ObjectiveWe conducted this multicity time-series study in Taiwan to evaluate the association between airborne NMHC exposure and cardiorespiratory hospital admissions. MethodsWe collected the daily mean concentrations of NMHC, fine particulate matter (PM2.5), ozone (O3), weather conditions, and daily hospital admission count for cardiorespiratory diseases between 2014 and 2017 from eight major cities of Taiwan. We applied an over-dispersed generalized additive Poisson model (GAM) with adjustment for temporal trends, seasonal variations, weather conditions, and calendar effects to compute the effect estimate for each city. Then we conducted a random-effects meta-analysis to pool the eight city-specific effect estimates to obtain the overall associations of NMHC exposure on lag0 day with hospital admissions for respiratory and circulatory diseases, respectively. ResultsOn average, a 0.1-ppm increase of lag0 NMHC demonstrated an overall 0.9% (95% CI: 0.4–1.3%) and 0.8% (95% CI: 0.4–1.2%) increment of hospital admissions for respiratory and circulatory diseases, respectively. Further analyses with adjustment for PM2.5 and O3 in the multi-pollutant model or sensitivity analyses with restricting the NMHC monitoring from the general stations only confirmed the robustness of the association between ambient NMHC exposure and cardiorespiratory hospitalizations. ConclusionOur findings provide robust evidence of higher cardiorespiratory hospitalizations in association with acute exposure to ambient NMHC in eight major cities of Taiwan.

Sources of ambient non-methane hydrocarbon compounds and their impacts on O3 formation during autumn, Beijing

The field observation of 54 non-methane hydrocarbon compounds (NMHCs) was conducted from September 1 to October 20 in 2020 during autumn in Haidian District, Beijing. The mean concentration of total NMHCs was 29.81 ± 11.39 ppbv during this period, and alkanes were the major components. There were typical festival effects of NMHCs with lower concentration during the National Day. Alkenes and aromatics were the dominant groups in ozone formation potential (OFP) and OH radical loss rate (LOH). The positive matrix factorization (PMF) running results revealed that vehicular exhaust became the biggest source in urban areas, followed by liquefied petroleum gas (LPG) usage, solvent usage, and fuel evaporation. The box model coupled with master chemical mechanism (MCM) was applied to study the impacts of different NMHCs sources on ozone (O3) formation in an O3 episode. The simulation results indicated that reducing NMHCs concentration could effectively suppress O3 formation. Moreover, reducing traffic-related emissions of NMHCs was an effective way to control O3 pollution at an urban site in Beijing.

Annual nonmethane hydrocarbon trends in Beijing from 2000 to 2019

High loads of ground-level ozone have occurred with the implementation of the Air Pollution Prevention and Control Action Plan. However, the long temporal variation in precursor nonmethane hydrocarbons (NMHCs) has rarely been studied. In this study, we examined the evolution of NMHCs in Beijing based on ambient measurements from 2000 to 2019. The results indicated that the annual variation of ambient NMHCs during 2000 and 2019 could be divided into two stages. The mixing ratios of NMHCs rapidly rose during 2000 and 2009 (1.76 ppbv/year) but exhibited a downward trend from 2009 to 2019 at rate of 0.80 ppbv/yr. Moreover, the notable decrease in alkenes and aromatics after 2009 led to a sharp decrease in the propylene-equivalent concentration (PEC) (-0.80 ppbv/year). Implementation of emission reduction measures in Beijing have effectively reduced the contribution of vehicle-related sources, but the contribution of solvent usage and fuel consumption increased, which will become the focus of VOC control in Beijing in the future.

Impact of Encouraging Vehicles to Refuel at Night on Ozone and Non-Methane Hydrocarbons (NMHCs): A Case Study in Ji’nan, China

Gasoline evaporation is a potential source of ambient non-methane hydrocarbons (NMHCs) during summer, and thus the policy of encouraging vehicles to refuel at night has been implemented to control ground-level ozone (O3) and NMHCs. In this study, NMHCs and trace gases were observed online at an urban site of Ji’nan during May–July in 2019 and 2020 to assess the impact of this policy. After the implementation of this policy, the average concentration of daily maximum 8 h moving average O3 decreased from 198 μg/m3 to 181 μg/m3. Meanwhile, the average mixing ratio of NMHCs decreased from 19.89 ppbv to 18.02 ppbv. Sources of NMHCs were then apportioned using the positive matrix factorization model. Four factors were resolved and identified, including vehicle exhaust, paint and solvents usage, gasoline evaporation, and biogenic emission. Relative contributions of these four sources were 52.5%, 20.6%, 18.3%, and 8.6%, respectively. After the implementation of this policy, relative contributions of gasoline evaporation in 1:00–4:00 increased from 20.2–22.7% to 25.4–28.2%, while those for 16:00–18:00 decreased from 16.8–18.7% to 13.9–15.7%. The non-linear relationship of O3 with NMHCs and NOx was investigated using a box model based on observations. Results suggest that O3 production was mainly controlled by NMHCs. Aromatics and alkenes were the key NMHC species in O3 formation. Furthermore, two scenarios of encouraging vehicles to refuel at night were designed to evaluate their impact on O3. The relative decreases of O3 peak concentrations were lower than 1%, indicating that this policy had a limited impact on O3 during the observation period.

Evaluating oil and gas contributions to ambient nonmethane hydrocarbon mixing ratios and ozone-related metrics in the Colorado Front Range

Recently, oil and natural gas (O&NG) production activities in the Denver-Julesburg Basin have expanded rapidly. Associated nonmethane hydrocarbon (NMHC) emissions contribute to photochemical formation of ground-level ozone and include benzene as well as other hazardous air pollutants. Using positive matrix factorization (PMF) and chemical mass balance (CMB) methods, we estimate how much O&NG activities and other sources contribute to morning NMHC mixing ratios measured from 2013 to mid-2016 at a site in Platteville, CO, in the Denver-Julesburg Basin, and at a contrasting site in downtown Denver. A novel adjoint sensitivity analysis method is then used to estimate corresponding contributions to ozone and ozone-linked mortality in the Denver region. Average 6–9 am NMHC mixing ratios in Platteville were seven times higher than those in Denver in 2013 but four times higher in 2016. CMB estimates that O&NG activities contributed to the Platteville (Denver) site an average of 96% (56%) of NMHC on a carbon basis while PMF indicated 92% (33%). Average vehicle-related contributions of NMHC are estimated as 41% by CMB and 53% by PMF in Denver. Estimates of the fractional contribution to potential ozone and ozone-linked mortality from O&NG activities are smaller while those from vehicles are larger than the NMHC contributions. CMB (PMF) indicate that greater than 78% (40%) of annual average benzene in Denver is attributable to vehicle emissions while greater than 75% (67%) of benzene in Platteville is attributable to O&NG activities.

Ambient Non-Methane Hydrocarbons (NMHCs) Measurements in Baoding, China: Sources and Roles in Ozone Formation

Ambient non-methane hydrocarbons (NMHCs) are important precursors of ozone (O3) and secondary organic aerosol (SOA). Online and offline measurements of NMHCs were conducted during September 2015 in Baoding, Hebei province of China, in order to investigate their sources and roles in ozone formation. Average levels of total NMHCs online measured at the urban site were 44.5 ± 26.7 ppb. Aromatics was the largest contributor to NMHCs levels and OH reactivity, with fraction of 27.1% and 35.9%, respectively. Based on offline measurements at eight sites, we found that toluene, ethylbenzene, and m,p-xylene displayed the highest level at the site close to automobile manufacturing factories, followed by downwind receptor sites and other sites. Positive matrix factorization (PMF) model was then used to analyze NMHCs sources. Four factors were identified, including traffic-related emission, automobile manufacturing coating, biogenic emission, and NG/LPG usage and background. Average relative contribution of automobile manufacturing coating to NMHCs levels during the entire online measurement period was 33.4%, and this value increased to 42% during two O3 pollution days. Sensitivity of O3 formation to NMHCs and NOX during an O3 pollution episode were analyzed using a box model based on observations. Relative incremental reactivity (RIR) results suggested that O3 formation was in NOx-titration regime (i.e., highly NMHCs-limited regime). Further scenario analyses on relationship of O3 formation with reduction of NOx and anthropogenic NMHCs (AHC) indicated that AHC and NOx should be reduced by a ratio greater than two and three to achieve 5% and 10% O3 control objectives, respectively. The largest RIR value for anthropogenic NMHC species was from xylenes, which were also an important contributor to SOA formation and dominantly from sources related to automobile manufacturing coating and traffic emission. This means reducing NMHCs emission from automobile manufacturing coating and traffic emission should be given priority for synergetic control of O3 and PM2.5.

Association of ambient non-methane hydrocarbons exposure with respiratory hospitalizations: A time series study in Taipei, Taiwan

Ambient hydrocarbons are important precursors of ground-level ozone and secondary organic aerosol formation. However, few studies have assessed the health impact of airborne hydrocarbons. We conducted this time series ecological study to evaluate the association of short-term airborne hydrocarbons exposure with hospital admissions for respiratory diseases, while controlling for co-exposure to criteria pollutants. Taipei air pollution and weather data for the period spanning from January 2010 to December 2017 were obtained from Taiwan Air Quality Monitoring Network. Subsequently, daily pollutant concentrations were linked with daily hospital admission counts for respiratory diseases into a time series data frame. The standard generalized additive Poisson model adjusted for temporal trends, seasonal variations, weather conditions, and calendar effects, was applied to examine the short-term associations of acute airborne hydrocarbon exposure with respiratory hospital admissions. Next, the robustness of the associations was tested using two-pollutant models with further adjustment for fine particulate matter (PM2.5) and gaseous pollutants. The results demonstrated that an interquartile range increase in non-methane hydrocarbon (NMHC) exposure on lag0 day (0.15 ppm) was associated with a 0.86% (95% confidence interval: 0.37%–1.36%), 2.06% (0.77%–3.38%), and 1.25% (0.31%–2.20%) increment in all-respiratory-disease-, asthma-, and chronic-obstructive-pulmonary-disease-linked hospital admissions, respectively. The associations were robust with further adjustment for co-exposure to PM2.5 and ozone. The acute effect estimate of methane on each respiratory category was sensitive to the co-pollutant adjustment and lost statistical significance in the two-pollutant models. In conclusion, we confirmed that airborne NMHC exposure increased the risk of respiratory-disease-related hospital admissions in Taipei; this information may aid in the regulation of hydrocarbon pollution.

Corrections to "Ambient Nonmethane Hydrocarbon Levels Along Colorado's Northern Front Range: Acute and Chronic Health Risks".

Corrections to "Ambient Nonmethane Hydrocarbon Levels Along Colorado's Northern Front Range: Acute and Chronic Health Risks".

Ambient Nonmethane Hydrocarbon Levels Along Colorado's Northern Front Range: Acute and Chronic Health Risks.

Oil and gas (O&G) facilities emit air pollutants that are potentially a major health risk for nearby populations. We characterized prenatal through adult health risks for acute (1 h) and chronic (30 year) residential inhalation exposure scenarios to nonmethane hydrocarbons (NMHCs) for these populations. We used ambient air sample results to estimate and compare risks for four residential scenarios. We found that air pollutant concentrations increased with proximity to an O&G facility, as did health risks. Acute hazard indices for neurological (18), hematological (15), and developmental (15) health effects indicate that populations living within 152 m of an O&G facility could experience these health effects from inhalation exposures to benzene and alkanes. Lifetime excess cancer risks exceeded 1 in a million for all scenarios. The cancer risk estimate of 8.3 per 10 000 for populations living within 152 m of an O&G facility exceeded the United States Environmental Protection Agency's 1 in 10 000 upper threshold. These findings indicate that state and federal regulatory policies may not be protective of health for populations residing near O&G facilities. Health risk assessment results can be used for informing policies and studies aimed at reducing and understanding health effects associated with air pollutants emitted from O&G facilities.

Characterization of non-methane hydrocarbons and their sources in an industrialized coastal city, Yangtze River Delta, China

Ningbo is a highly industrialized city in the coastal area of the Yangtze River Delta (YRD), China. Large emissions and transport of non-methane hydrocarbons (NMHCs) may contribute to regional ozone (O3) and particulate matter (PM) pollution; however, the concentrations and sources of ambient NMHCs have not yet been investigated in Ningbo. In this study, ambient NMHCs were measured at two residential (SZ and CX) and two industrial (ZH and BL) sites and one suburban (XS) site over ten consecutive days in each season (10–20 December 2012 in winter, 14–23 April 2013 in spring, 15–24 July 2013 in summer, 22–31 October 2013, in autumn). A positive matrix factorization (PMF) model using multiple site data was deployed to explore the source contributions and their spatial and seasonal characteristics. The measurement results showed obvious seasonal variations in ambient NMHC concentrations (ranging from 17.89–28.48ppbv); chemical compositions were similar among the five sampling sites. PMF analysis showed that the petrochemical industry was the largest contributor (an average of 35.64%) to ambient NMHCs, while contributions of smaller sources (i.e., chemical and paint industries [14.34%], fuel and tank evaporation [16.02%], and residential solvent usage [7.24%]) showed spatial variations. Liquefied petroleum gas and fuel and tank evaporation contributed more in summer and autumn, while the contribution of the chemical and paint industries was greater in spring and winter. An evaluation of the ozone formation potential and secondary organic aerosol potential suggested that petrochemical and solvent-related sources were key parameters in mitigation of secondary pollutant formation. Seasonal variations in source contributions should be considered when formulating an effective NMHC abatement strategy.

Concentrations and sources of non-methane hydrocarbons (NMHCs) from 2005 to 2013 in Hong Kong: A multi-year real-time data analysis

To understand the long-term variations of nonmethane hydrocarbons (NMHCs) and their emission sources, real-time speciated NMHCs have been monitored in Hong Kong since 2005. Data analysis showed that the concentrations of C3–C5 and C6–C7 alkanes slightly increased from 2005 to 2013 at a rate of 0.0015 and 0.0005 μg m−3 yr−1 (p < 0.05), respectively, while aromatics decreased at a rate of 0.006 μg m−3 yr−1 (p < 0.05). Positive Matrix Factorization (PMF) model was applied to identify and quantify the NMHC sources. Vehicular exhaust, gasoline evaporation and liquefied petroleum gas (LPG) usage, consumer product and printing, architectural paints, and biogenic emissions were identified and on average accounted for 20.2 ± 6.2%, 25.4 ± 6.3%, 32.6 ± 5.8%, 21.5 ± 4.5%, and 3.3 ± 1.5% of the ambient NMHC concentrations, respectively. From 2005 to 2013, the contributions of both traffic-related sources and solvent-related sources showed no significant changes, different from the trends in emission inventory. On O3 episode days dominated by local air masses, the increase ratio of NMHC species from non-episode to episode days was found to be a natural function of the reactivity of NMHC species, suggesting that photochemical reaction would significantly change the NMHCs composition between emission sources and the receptors. Effect of photochemical reaction loss on receptor-oriented source apportionment analysis needs to be quantified in order to identify the NMHCs emission sources on O3 episode days.

Reconstruction of Northern Hemisphere 1950–2010 atmospheric non-methane hydrocarbons

Abstract. The short-chain non-methane hydrocarbons (NMHC) are mostly emitted into the atmosphere by anthropogenic processes. Recent studies have pointed out a tight linkage between the atmospheric mole fractions of the NMHC ethane and the atmospheric growth rate of methane. Consequently, atmospheric NMHC are valuable indicators for tracking changes in anthropogenic emissions, photochemical ozone production, and greenhouse gases. This study investigates the 1950–2010 Northern Hemisphere atmospheric C2–C5 NMHC ethane, propane, i-butane, n-butane, i-pentane, and n-pentane by (a) reconstructing atmospheric mole fractions of these trace gases using firn air extracted from three boreholes in 2008 and 2009 at the North Greenland Eemian Ice Drilling (NEEM) site and applying state-of-the-art models of trace gas transport in firn, and by (b) considering eight years of ambient NMHC monitoring data from five Arctic sites within the NOAA Global Monitoring Division (GMD) Cooperative Air Sampling Network. Results indicate that these NMHC increased by ~40–120% after 1950, peaked around 1980 (with the exception of ethane, which peaked approximately 10 yr earlier), and have since dramatically decreased to be now back close to 1950 levels. The earlier peak time of ethane vs. the C3–C5 NMHC suggests that different processes and emissions mitigation measures contributed to the decline in these NMHC. The 60 yr record also illustrates notable increases in the ratios of the isomeric iso-/n-butane and iso-/n-pentane ratios. Comparison of the reconstructed NMHC histories with 1950–2000 volatile organic compounds (VOC) emissions data and with other recently published ethane trend analyses from ambient air Pacific transect data showed (a) better agreement with North America and Western Europe emissions than with total Northern Hemisphere emissions data, and (b) better agreement with other Greenland firn air data NMHC history reconstructions than with the Pacific region trends. These analyses emphasize that for NMHC, having atmospheric lifetimes on the order of &lt; 2 months, the Greenland firn air records are primarily a representation of Western Europe and North America emission histories.

Prediction of non-methane hydrocarbons in Kuwait using regression and Bayesian kriged Kalman model

This article describes the hierarchical Bayesian approach for predicting average hourly concentrations of ambient non-methane hydrocarbons (NMHC) in Kuwait where records of six monitor stations located in different sites are observed at successive time points. Our objective is to predict the concentration level of NMHC in unmonitored areas. Here an attempt is made for the prediction of unmeasured concentration of NMHC at two additional locations in Kuwait. We will implement a kriged Kalman filter (KKF) hierarchical Bayesian approach assuming a Gaussian random field, a technique that allows the pooling of data from different sites in order to predict the exposure of the NMHC in different regions of Kuwait. In order to increase the accuracy of the KKF we will use other statistical models such as imputation, regression, principal components, and time series analysis in our approach. We considered four different types of imputation techniques to address the missing data. At the primary level, the logarithmic field is modeled as a trend plus Gaussian stochastic residual model. The trend model depends on hourly meteorological predictors which are common to all sites. The residuals are then modeled using KKF, and the prediction equation is derived conditioned on adjoining hours. On this basis we developed a spatial predictive distribution for these residuals at unmonitored sites. By transforming the predicted residuals back to the original data scales, we can impute Kuwait’s hourly non-methane hydrocarbons field.

Non-methane Hydrocarbons and Their Ozone Formation Potentials in Foshan, China

Concentrations of non-methane hydrocarbons (NMHCs) were measured to investigate their temporal variations and major sources, and to explore the ozone formation potentials (OFP) of each NMHCs for the first time in December 2008 in Foshan. Ethane, propane, n-butane, i-pentane, 2,3-dimethylbutane, ethene, propene, ethyne, benzene and toluene were the 10 most abundant hydrocarbons, accounting for 82% of the concentration of total NMHCs. Concentrations of these hydrocarbons as well as their fractional contributions to the total NMHCs were higher in the morning and evening than in the afternoon, consistent with the variations in vehicle volumes during these periods. This suggests that the vehicular emission was likely the major source of NMHCs at this site. The mean B/T ratio (0.45 ± 0.24) further supported vehicular emission as the main source of the ambient NMHCs except for aromatic hydrocarbons. These aromatic hydrocarbons were mainly from solvent evaporation, as indicated by the diurnal variations in the ratios of toluene and m/p-xylene to benzene. The results from factor analysis also showed that combustion process and solvent usage were the major sources of NMHCs. On average, total Prop-Equiv and OFP were 153.0 ppbc and 863.4 μg/m 3 , respectively. Based on MIR (maximum incremental reactivity) scale, the leading contributors to OFP in decreasing concentrations were ethene, toluene, propene, i-pentane, m/p-xylene, 1-butene, ethylbenzene, o-xylene, 2,3-dimethylbutane and trans-2-butene, which in total explained 77% of the total OFP. Ranking by Prop-Equiv, the top 10 species were propene, toluene, ethene, 1-butene, i-pentane, m/pxylene, isoprene, 2,3-dimethylbutane, trans-2-butene and ethylbenzene, accounting for 66% of the total Prop-Equiv. Thus, alkenes played the most important role in O3 formation, followed by aromatics and alkanes during the study periods in Foshan.

Variation of ambient non-methane hydrocarbons in Beijing city in summer 2008

Abstract. In conjunction with hosting the 2008 Beijing Olympics, the municipal government implemented a series of stringent air quality control measures. To assess the impacts on variation of ambient non-methane hydrocarbons (NMHCs), the whole air was sampled by canisters at one urban site and two suburban sites in Beijing, and 55 NMHC species were quantified by gas chromatography equipped with a quadrupole mass spectrometer and a flame ionization detector (GC/MSD/FID) as parts of the field Campaign for the Beijing Olympic Games Air Quality program (CareBeijing). According to the control measures, the data were presented according to four periods: 18–30 June, 8–19 July, 15–24 August (during the Olympic Games), and 6–15 September (during the Paralympic Games). Compared with the levels in June, the mixing ratios of NMHCs obtained in the Olympic and Paralympic Games periods were reduced by 35% and 25%, respectively. Source contributions were calculated using a chemical mass balance model (CMB 8.2). After implementing the control measures, emissions from target sources were obviously reduced, and reductions in vehicle exhaust could explain 48–82% of the reductions of ambient NMHCs. Reductions in emissions from gasoline evaporation, paint and solvent use, and the chemical industry contributed 9–40%, 3–24%, and 1–5%, respectively, to reductions of ambient NMHCs. Sources of liquefied petroleum gas (LPG) and biogenic emissions were not controlled, and contributions from these sources from July to September were stable or even higher than in June. Ozone formation potentials (OFPs) were calculated for the measured NMHCs. The total OFPs during the Olympic and Paralympic Games were reduced by 48% and 32%, respectively, compared with values in June. Reductions in the OFPs of alkenes and aromatics explained 77–92% of total OFP reductions. The alkenes and aromatics were mainly from vehicle exhausts, and reductions of vehicle exhaust gases explained 67–87% of reductions in alkenes and 38–80% of reductions in aromatics. These findings demonstrate the effectiveness of the air quality control measures enacted for the 2008 Olympics and indicate that controlling vehicular emissions could be the most important measure to improve air quality in Beijing.