Distribution Of Emission Factors Research Articles

In Situ Sampling of NOx Emissions from United States Natural Gas Flares Reveals Heavy-Tail Emission Characteristic.

Natural gas flaring is a common practice employed in many United States (U.S.) oil and gas regions to dispose of gas associated with oil production. Combustion of predominantly hydrocarbon gas results in the production of nitrogen oxides (NOx). Here, we present a large field data set of in situ sampling of real world flares, quantifying flaring NOx production in major U.S. oil production regions: the Bakken, Eagle Ford, and Permian. We find that a single emission factor does not capture the range of the observed NOx emission factors within these regions. For all three regions, the median emission factors fall within the range of four emission factors used by the Texas Commission for Environmental Quality. In the Bakken and Permian, the distribution of emission factors exhibits a heavy tail such that basin-average emission factors are 2-3 times larger than the value employed by the U.S. Environmental Protection Agency. Extrapolation to basin scale emissions using auxiliary satellite assessments of flare volumes indicates that NOx emissions from flares are skewed, with 20%-30% of the flares responsible for 80% of basin-wide flaring NOx emissions. Efforts to reduce flaring volume through alternative gas capture methods would have a larger impact on the NOx oil and gas budget than current inventories indicate.

Comparing the Use of High- to Low-Cost Black Carbon and Carbon Dioxide Sensors for Characterizing On-Road Diesel Truck Emissions.

The exhaust plume capture method is a commonly used approach to measure pollutants emitted by in-use heavy-duty diesel trucks. Lower cost sensors, if used in place of traditional research-grade analyzers, could enable wider application of this method, including use as a monitoring tool to identify high-emitting trucks that may warrant inspection and maintenance. However, low-cost sensors have for the most part only been evaluated under ambient conditions as opposed to source-influenced environments with rapidly changing pollutant concentrations. This study compared black carbon (BC) emission factors determined using different BC and carbon dioxide (CO2) sensors that range in cost from $200 to $20,000. Controlled laboratory experiments show that traditional zero and span steady-state calibration checks are not robust indicators of sensor performance when sampling short duration concentration peaks. Fleet BC emission factor distributions measured at two locations at the Port of Oakland in California with 16 BC/CO2 sensor pairs were similar, but unique sensor pairs identified different high-emitting trucks. At one location, the low-cost PP Systems SBA-5 agreed on the classification of 90% of the high emitters identified by the LI-COR LI-7000 when both were paired with the Magee Scientific AE33. Conversely, lower cost BC sensors when paired with the LI-7000 misclassified more than 50% of high emitters when compared to the AE33/LI-7000. Confidence in emission factor quantification and high-emitter identification improves with larger integrated peak areas of CO2 and especially BC. This work highlights that sensor evaluation should be conducted under application-specific conditions, whether that be for ambient air monitoring or source characterization.

In-Use Performance and Durability of Particle Filters on Heavy-Duty Diesel Trucks.

Diesel particle filters (DPFs) are standard equipment on heavy-duty diesel trucks with 2007 and newer engines in the U.S. This study evaluates the performance and durability of these filters. Black carbon (BC) emission rates from several thousand heavy-duty trucks were measured at the Port of Oakland and Caldecott Tunnel over multiple years as California regulations accelerated the adoption of DPFs. As DPF use increased, fleet-average BC emissions decreased, and emission factor distributions became more skewed. Relative to 2004-2006 engines without filters, DPFs reduced BC emission rates by 65-70% for 2007-2009 engines and by >90% for 2010+ engines. Average BC emission rates for 2007-2009 engines increased by 50-67% in 2015 relative to measurements made 1-2 years earlier. Some trucks in this cohort have become high-emitters, indicating that some DPFs are no longer working well. At the Port, where DPFs were universal in 2015, high-emitting 2007-2009 engines (defined here as emitting >1 g BC kg-1) comprised 7% of the fleet but were responsible for 65% of the total BC emitted. These observations raise concerns about DPF durability and the prospects for fully mitigating adverse effects of diesel particulate matter on human health and the environment.

Country- and manufacturer-level attribution of air quality impacts due to excess NOx emissions from diesel passenger vehicles in Europe

In 2015, diesel cars accounted for 41.3% of the total passenger car fleet in Europe. While harmonized emissions limits are implemented at the EU level, on-road emissions of diesel cars have been found to be up to 16 times higher than those measured in test stands. These excess emissions have been estimated to result in increased PM2.5 and ozone exposure causing approximately 5000 premature mortalities per year in Europe. Interventions aimed at mitigating these damages need to take into account the physical and political boundaries in Europe, where emissions from one country may have an impact on neighboring populaces (trans-boundary impacts). To date, the trans-boundary implications of excess NOx emissions in Europe are not understood and only excess NOx emissions have only been studied at the fleet level and for Volkswagen group cars. In this study, a distribution of emission factors is derived from existing on-road measurements for 10 manufacturers, covering 90% of all new vehicle registrations in Europe from 2000 to 2015. These distributions are combined with inventory data and driving behavior to quantify excess emissions of nitrogen oxides (NOx) in Europe in 2015. To quantify the changes in PM2.5 and ozone concentrations resulting from these emissions, we use a state-of-the-art chemical transport model (GEOS-Chem). Concentration-response functions from the epidemiological literature are applied to estimate the premature mortality outcomes and the number of life-years lost associated with degraded air quality. Uncertainty in the input parameters is propagated through the analysis using a Monte Carlo approach. We find that 70% of the total health impacts from excess NOx are due to trans-boundary emissions. For example, 61% of the impacts in Germany of total excess NOx emissions are caused by emissions released in other countries. These results highlight the need for a coordinated policy response at the European level. In addition, we find that total emissions accounting for country-specific fleet mixes and driving behaviors vary between manufacturers by a factor of 10 and mortality impacts per kilometer driven by a factor of 8. Finally, we find that if all manufacturers reduced emissions of the vehicles currently on the road to those of the best-performing manufacturer in the corresponding Euro standard, approximately 1900 premature deaths per year could be avoided.

Field measurements of solid-fuel cookstove emissions from uncontrolled cooking in China, Honduras, Uganda, and India

Cookstoves have wide-reaching impacts on human health, air quality, and the climate. We measured emissions from uncontrolled cooking in 41 households in China, Honduras, Uganda, and India using a portable sampler. Test sites were chosen to cover a range of stove types (traditional and “improved”), fuels (wood, charcoal and coal), and cooking practices. We report test-integrated fuel-based emission factors (EFs) of fine particulate matter (PM2.5) mass, organic carbon (OC), elemental carbon (EC), as well as real time EFs of carbon monoxide (CO), black carbon (BC), total particle number, and particle size distributions. There was substantial house-to-house variability in emissions; the distribution of EFs were also highly positively skewed by several “superemitter” stoves in China (those with PM2.5 EFs 5–20 times greater than the median value). The highest PM2.5 mass emission factors were measured in China (median:10.3 g/kg-fuel), and the lowest in Uganda (median: 1.7 g/kg-fuel). The median PM2.5 mass EFs in wood-burning stoves in Honduras and India were similar: 3.7 g/kg-fuel and 4.1 g/kg-fuel, respectively. However, Indian stoves had higher EC EFs then Honduran stoves, demonstrating that emissions depend on more that fuel type; regional differences, such as cooking styles and stove design, may influence aerosol properties as well. Coal and charcoal stoves had higher OC:EC than wood stoves. The differences between the CO, PM2.5, and OC:EC ratios of “improved” and traditional stoves in India and Honduras were not statistically significant. To the best of our knowledge, we report the first cookstove source size distributions measurements from uncontrolled in-home cooking. These distributions varied between countries, which will influence local radiative effects. Particle size distributions from stoves tested in China, Honduras, and India were unimodal in the size range measured, with geometric mean diameters (GMDs) of 66 nm, 48 nm, and 76 nm, respectively. The median GMD of particles emitted from Ugandan charcoal stoves was 39, and when all tests are averaged, the resulting distribution appears tri-modal, with modes near 15, 30, and 100 nm. Real-time emissions data reveal high BC and particle number emissions during startup and fuel additions, which can be seen in the positively skewed distributions. Emissions of BC were most skewed, indicating that they were highly event-driven, followed by total particle number. CO emissions were more evenly spread across cooking events.

An Improved Approach to Estimate Methane Emissions from Coal Mining in China.

China, the largest coal producer in the world, is responsible for over 50% of the total global methane (CH4) emissions from coal mining. However, the current emission inventory of CH4 from coal mining has large uncertainties because of the lack of localized emission factors (EFs). In this study, province-level CH4 EFs from coal mining in China were developed based on the data analysis of coal production and corresponding discharged CH4 emissions from 787 coal mines distributed in 25 provinces with different geological and operation conditions. Results show that the spatial distribution of CH4 EFs is highly variable with values as high as 36 m3/t and as low as 0.74 m3/t. Based on newly developed CH4 EFs and activity data, an inventory of the province-level CH4 emissions was built for 2005-2010. Results reveal that the total CH4 emissions in China increased from 11.5 Tg in 2005 to 16.0 Tg in 2010. By constructing a gray forecasting model for CH4 EFs and a regression model for activity, the province-level CH4 emissions from coal mining in China are forecasted for the years of 2011-2020. The estimates are compared with other published inventories. Our results have a reasonable agreement with USEPA's inventory and are lower by a factor of 1-2 than those estimated using the IPCC default EFs. This study could help guide CH4 mitigation policies and practices in China.

Implementation of the MEGAN (v2.1) biogenic emission model in the ECHAM6-HAMMOZ chemistry climate model

Abstract. A biogenic emission scheme based on the Model of Emissions of Gases and Aerosols from Nature (MEGAN) version 2.1 (Guenther et al., 2012) has been integrated into the ECHAM6-HAMMOZ chemistry climate model in order to calculate the emissions from terrestrial vegetation of 32 compounds. The estimated annual global total for the reference simulation is 634 Tg C yr−1 (simulation period 2000–2012). Isoprene is the main contributor to the average emission total, accounting for 66 % (417 Tg C yr−1), followed by several monoterpenes (12 %), methanol (7 %), acetone (3.6 %), and ethene (3.6 %). Regionally, most of the high annual emissions are found to be associated with tropical regions and tropical vegetation types. In order to evaluate the implementation of the biogenic model in ECHAM-HAMMOZ, global and regional biogenic volatile organic compound (BVOC) emissions of the reference simulation were compared to previous published experiment results with MEGAN. Several sensitivity simulations were performed to study the impact of different model input and parameters related to the vegetation cover and the ECHAM6 climate. BVOC emissions obtained here are within the range of previous published estimates. The large range of emission estimates can be attributed to the use of different input data and empirical coefficients within different setups of MEGAN. The biogenic model shows a high sensitivity to the changes in plant functional type (PFT) distributions and associated emission factors for most of the compounds. The global emission impact for isoprene is about −9 %, but reaches +75 % for α-pinene when switching from global emission factor maps to PFT-specific emission factor distributions. The highest sensitivity of isoprene emissions is calculated when considering soil moisture impact, with a global decrease of 12.5 % when the soil moisture activity factor is included in the model parameterization. Nudging ECHAM6 climate towards ERA-Interim reanalysis has an impact on the biogenic emissions, slightly lowering the global total emissions and their interannual variability.

Investigating the real-world emission characteristics of light-duty gasoline vehicles and their relationship to local socioeconomic conditions in three communities in Los Angeles, California

ABSTRACTThis paper discusses results from a vehicular emissions research study of over 350 vehicles conducted in three communities in Los Angeles, CA, in 2010 using vehicle chase measurements. The study explores the real-world emission behavior of light-duty gasoline vehicles, characterizes real-world super-emitters in the different regions, and investigates the relationship of on-road vehicle emissions with the socioeconomic status (SES) of the region. The study found that in comparison to a 2007 earlier study in a neighboring community, vehicle emissions for all measured pollutants had experienced a significant reduction over the years, with oxides of nitrogen (NOX) and black carbon (BC) emissions showing the largest reductions. Mean emission factors of the sampled vehicles in low-SES communities were roughly 2–3 times higher for NOX, BC, carbon monoxide, and ultrafine particles, and 4–11 times greater for fine particulate matter (PM2.5) than for vehicles in the high-SES neighborhood. Further analysis indicated that the emission factors of vehicles within a technology group were also higher in low-SES communities compared to similar vehicles in the high-SES community, suggesting that vehicle age alone did not explain the higher vehicular emission in low-SES communities.Evaluation of the emission factor distribution found that emissions from 12% of the sampled vehicles were greater than five times the mean from all of the sampled fleet, and these vehicles were consequently categorized as “real-world super-emitters.” Low-SES communities had approximately twice as many super-emitters for most of the pollutants as compared to the high-SES community. Vehicle emissions calculated using model-year-specific average fuel consumption assumptions suggested that approximately 5% of the sampled vehicles accounted for nearly half of the total CO, PM2.5, and UFP emissions, and 15% of the vehicles were responsible for more than half of the total NOX and BC emissions from the vehicles sampled during the study.Implications: This study evaluated the real-world emission behavior and super-emitter distribution of light-duty gasoline vehicles in California, and investigated the relationship of on-road vehicle emissions with local socioeconomic conditions. The study observed a significant reduction in vehicle emissions for all measured pollutants when compared to an earlier study in Wilmington, CA, and found a higher prevalence of high-emitting vehicles in low-socioeconomic-status communities. As overall fleet emissions decrease from stringent vehicle emission regulations, a small fraction of the fleet may contribute to a disproportionate share of the overall on-road vehicle emissions. Therefore, this work will have important implications for improving air quality and public health, especially in low-SES communities.

Effects of Particle Filters and Selective Catalytic Reduction on Heavy-Duty Diesel Drayage Truck Emissions at the Port of Oakland.

Effects of fleet modernization and use of diesel particle filters (DPF) and selective catalytic reduction (SCR) on heavy-duty diesel truck emissions were studied at the Port of Oakland in California. Nitrogen oxides (NOx), black carbon (BC), particle number (PN), and size distributions were measured in the exhaust plumes of ∼1400 drayage trucks. Average NOx, BC, and PN emission factors for newer engines (2010-2013 model years) equipped with both DPF and SCR were 69 ± 15%, 92 ± 32%, and 66 ± 35% lower, respectively, than 2004-2006 engines without these technologies. Intentional oxidation of NO to NO2 for DPF regeneration increased tailpipe NO2 emissions, especially from older (1994-2006) engines with retrofit DPFs. Increased deployment of advanced controls has further skewed emission factor distributions; a small number of trucks emit a disproportionately large fraction of total BC and NOx. The fraction of DPF-equipped drayage trucks increased from 2 to 99% and the median engine age decreased from 11 to 6 years between 2009 and 2013. Over this period, fleet-average BC and NOx emission factors decreased by 76 ± 22% and 53 ± 8%, respectively. Emission changes occurred rapidly compared to what would have been observed due to natural (i.e., unforced) turnover of the Port truck fleet. These results provide a preview of more widespread emission changes expected statewide and nationally in the coming years.

Emission factors of SO<sub>2</sub>, NO<sub><i>x</i></sub> and particles from ships in Neva Bay from ground-based and helicopter-borne measurements and AIS-based modeling

Abstract. Emission factors of SO2, NOx and size-distributed particle numbers were measured for approximately 300 different ships in the Gulf of Finland and Neva Bay area during two campaigns in August/September 2011 and June/July 2012. The measurements were carried out from a harbor vessel and from an Mi-8 helicopter downwind of passing ships. Other measurements were carried out from shore sites near the island of Kronstadt and along the Neva River in the urban area of Saint Petersburg. Most ships were running at reduced speed (10 kn), i.e., not at their optimal load. Vessels for domestic and international shipping were monitored. It was seen that the distribution of the SO2 emission factors is bi-modal, with averages of 4.6 and 18.2 gSO2 kgfuel-1 for the lower and the higher mode, respectively. The emission factors show compliance with the 1% fuel sulfur content Sulfur Emission Control Areas (SECA) limit for 90% of the vessels in 2011 and 97% in 2012. The distribution of the NOx emission factor is mono-modal, with an average of 58 gNOx kgfuel-1. The corresponding emission related to the generated power yields an average of 12.1 gNOx kWh−1. The distribution of the emission factors for particulate number shows that nearly 90% of all particles in the 5.6 nm to 10 μm size range were below 70 nm in diameter. The distribution of the corresponding emission factors for the mass indicates two separated main modes, one for particles between 30 and 300 nm and the other for above 2 μm. The average particle emission factors were found to be in the range from 0.7 to 2.7 × 1016 particles kgfuel-1 and 0.2 to 3.4 gPM kgfuel-1, respectively. The NOx and particulate emissions are comparable with other studies. The measured emission factors were compared, for individual ships, to modeled ones using the Ship Traffic Emission Assessment Model (STEAM) of the Finnish Meteorological Institute. A reasonably good agreement for gaseous sulfur and nitrogen emissions can be seen for ships in international traffic, but significant deviations are found for inland vessels. Regarding particulate mass, the values of the modeled data are about 2–3 times higher than the measured results, which probably reflects the assumptions made in the modeled fuel sulfur content. The sulfur contents in the fuel retrieved from the measurements were lower than the previously used assumptions by the City of Saint Petersburg when carrying out atmospheric modeling, and using these measurements it was possible to better assess the impact of shipping on air quality.

Characterization of particulate matter emissions from on-road gasoline and diesel vehicles using a soot particle aerosol mass spectrometer

Abstract. Particulate matter (PM) emissions were measured in July 2010 from on-road motor vehicles driving through a highway tunnel in the San Francisco Bay area. A soot particle aerosol mass spectrometer (SP-AMS) was used to measure the chemical composition of PM emitted by gasoline and diesel vehicles at high time resolution. Organic aerosol (OA) and black carbon (BC) concentrations were measured during various time periods that had different levels of diesel influence, as well as directly in the exhaust plumes of individual heavy-duty (HD) diesel trucks. BC emission factor distributions for HD trucks were more skewed than OA distributions (N = 293), with the highest 10% of trucks accounting for 56 and 42% of total measured BC and OA emissions, respectively. OA mass spectra measured for HD truck exhaust plumes show cycloalkanes are predominate in exhaust OA emissions relative to saturated alkanes (i.e., normal and iso-paraffins), suggesting that lubricating oil rather than fuel is the dominant source of primary organic aerosol (POA) emissions in diesel vehicle exhaust. This finding is supported by the detection of trace elements such as zinc and phosphorus in the exhaust plumes of individual trucks. Trace elements were emitted relative to total OA at levels that are consistent with typical weight fractions of commonly used additives present in lubricating oil. A comparison of measured OA and BC mass spectra across various sampling periods revealed a high degree of similarity in OA and BC emitted by gasoline and diesel engines. This finding indicates a large fraction of OA in gasoline exhaust is lubricant-derived as well. The similarity in OA and BC mass spectra for gasoline and diesel engine exhaust is likely to confound ambient source apportionment efforts to determine contributions to air pollution from these two important sources.

몬테 카를로 시뮬레이션을 이용한 소나무 탄소배출계수의 불확도 평가

본 연구의 목적은 몬테 카를로 시뮬레이션을 이용하여 소나무 탄소배출계수 자료의 확률밀도를 추정하고 불확도를 제시하는데 있다. 이용된 탄소배출계수는 목재기본밀도, 바이오매스확장계수, 뿌리함량비이고 4개의 확률밀도 함수(정규분포, 로그정규분포, 감마분포, 와이불 분포)를 고려하였다. 2-표본 콜모그로프-스미르노프 검정통계량과 누적밀도그림을 비교하여 최적의 확률밀도함수를 선정하고 상한과 하한의 불확도를 제시하였다. 본 연구의 결과에 의하면, 각 탄소배출계수에서 추정된 확률밀도함수는 강원지방소나무에서 목재기본밀도는 감마분포, 바이오매스확장계수는 로그정규분포, 뿌리함량비는 정규분포이고 중부지방소나무에서 목재기본밀도는 정규분포, 바이오매스확장계수는 감마분포, 뿌리함량비는 감마분포를 나타내었다. 강원지방소나무 탄소배출계수의 불확도는 상한에서 62.1%, 하한에서 -52.6%이고 중부지방소나무는 상한에서 43.9%, 하한에서 -34.5%를 나타내었다. The purpose of this study was to calculate uncertainty of emission factor collected data and to evaluate the applicability of Monte Carlo simulation technique. To estimate the distribution of emission factors (Such as Basic wood density, Biomass expansion factor, and Root-to-shoot ratio), four probability density functions (Normal, Lognormal, Gamma, and Weibull) were used. The two sample Kolmogorov-Smirnov test and cumulative density figure were used to compare the optimal probability density function. It was observed that the basic wood density showed the gamma distribution, the biomass expansion factor results the log-normal distribution, and root-shoot ratio showd the normal distribution for Pinus densiflora in the Gangwon region; the basic wood density was the normal distribution, the biomass expansion factor was the gamma distribution, and root-shoot ratio was the gamma distribution for Pinus densiflora in the central region, respectively. The uncertainty assessment of emission factor were upper 62.1%, lower -52.6% for Pinus densiflora in the Gangwon region and upper 43.9%, lower -34.5% for Pinus densiflora in the central region, respectively.

PCDD/DF and co-planar PCB emissions from crematories in Japan

Japan implemented dioxin emission guidelines for crematories in 2000, but the effects of the new guidelines have not been fully evaluated. In this study, concentrations of polychlorinated dibenzodioxins/dibenzofurans (PCDDs/DFs) and co-planar polychlorinated biphenyls (co-PCBs) were measured in flue gas, fly ash, and bottom ash (mainly bone) from several crematories as a follow-up investigation. Total concentrations (O2 12% normalized) of PCDDs/DFs and co-PCBs in flue gas ranged from 4.2to540ng/mN3, and toxic equivalent concentrations ranged from 0.000053 to 11ng-TEQ/mN3. Based on these measurements, the average emission factor was estimated to be 1400ng-TEQ/body. This is approximately one-third the emission factor recorded in 1999. The emission factor distributions from 1999 and our study in 2007 were log-normally distributed. Emission factors were significantly lower in 2007 than in 1999, which suggests that the guidelines have been effective in reducing dioxin emissions. Meanwhile, toxic equivalent concentrations in fly ash ranged from 0.014 to 13ng-TEQg−1. Higher dioxin concentrations in fly ash were observed in facilities that used a heat exchanger as a flue-gas cooling device. Because the concentrations of PCDDs/DFs and co-PCBs in flue gas were also elevated after heat exchangers during the investigation of PCDD/DF- and co-PCB-removal behaviors, secondary formation of PCDDs/DFs and co-PCBs on heat exchanger surfaces unambiguously occurred.

Evaluation of two isoprene emission models for use in a long-range air pollution model

Abstract. Knowledge about isoprene emissions and concentration distribution is important for chemistry transport models (CTMs), because isoprene acts as a precursor for tropospheric ozone and subsequently affects the atmospheric concentrations of many other atmospheric compounds. Isoprene has a short lifetime, and hence it is very difficult to evaluate its emission estimates against measurements. For this reason, we coupled two isoprene emission models with the Danish Eulerian Hemispheric Model (DEHM), and evaluated the simulated background ozone concentrations based on different models for isoprene emissions. In this research, results of using the two global biogenic emission models; GEIA (Global Emissions Inventory Activity) and MEGAN (the global Model of Emissions of Gases and Aerosols from Nature) are compared and evaluated. The total annual emissions of isoprene for the year 2006 estimated by using MEGAN is 592 Tg yr−1 for an extended area of the Northern Hemisphere, which is 21% higher than that estimated by using GEIA. The overall feature of the emissions from the two models is quite similar, but differences are found mainly in Africa's savannah and in the southern part of North America. Differences in spatial distribution of emission factors are found to be a key source of these discrepancies. In spite of the short life-time of isoprene, a direct evaluation of isoprene concentrations using the two biogenic emission models in DEHM has been made against available measurements in Europe. Results show an agreement between two models simulations and the measurements in general and that the CTM is able to simulate isoprene concentrations. Additionally, investigation of ozone concentrations resulting from the two biogenic emission models show that isoprene simulated by MEGAN strongly affects the ozone production in the African savannah; the effect is up to 10% more than that obtained using GEIA. In contrast, the impact of using GEIA is higher in the Amazon region with more than 8% higher ozone concentrations compared to that of using MEGAN. Comparing the ozone concentrations obtained by DEHM using the two different isoprene models with measurements from Europe and North America, show an agreement on the hourly, mean daily and daily maximum values. However, the average of ozone daily maximum value simulated by using MEGAN is slightly closer to the measured value for the average of all measuring sites in Europe.

Effects of Diesel Particle Filter Retrofits and Accelerated Fleet Turnover on Drayage Truck Emissions at the Port of Oakland

Heavy-duty diesel drayage trucks have a disproportionate impact on the air quality of communities surrounding major freight-handling facilities. In an attempt to mitigate this impact, the state of California has mandated new emission control requirements for drayage trucks accessing ports and rail yards in the state beginning in 2010. This control rule prompted an accelerated diesel particle filter (DPF) retrofit and truck replacement program at the Port of Oakland. The impact of this program was evaluated by measuring emission factor distributions for diesel trucks operating at the Port of Oakland prior to and following the implementation of the emission control rule. Emission factors for black carbon (BC) and oxides of nitrogen (NO(x)) were quantified in terms of grams of pollutant emitted per kilogram of fuel burned using a carbon balance method. Concentrations of these species along with carbon dioxide were measured in the exhaust plumes of individual diesel trucks as they drove by en route to the Port. A comparison of emissions measured before and after the implementation of the truck retrofit/replacement rule shows a 54 ± 11% reduction in the fleet-average BC emission factor, accompanied by a shift to a more highly skewed emission factor distribution. Although only particulate matter mass reductions were required in the first year of the program, a significant reduction in the fleet-average NO(x) emission factor (41 ± 5%) was observed, most likely due to the replacement of older trucks with new ones.

Assessment of German nitrous oxide emissions using empirical modelling approaches

Direct nitrous oxide (N2O) emissions from agricultural soils contribute considerably to anthropogenic GHG emissions. Albeit a key source of emissions in many countries, direct N2O emissions are still calculated and reported to the United Nations Convention on Climate Change using default emission factors defined in the IPCC guidelines (IPCC 1996, 2006). It is known that processes controlling production and transport of N2O are highly sensitive to environmental conditions defined by weather, soil and management. The accuracy of N2O emission budgets and the efficiency of mitigation can be improved if those dependencies are considered with regionalized emission factors. In this study an empirical method originating from soft computing techniques based on measured data is developed and applied to quantify direct N2O emissions from agricultural soils at field and national level in Germany between 1990 and 2005. The method is used to derive maps of emission factor distribution of direct N2O emissions of agricultural land in Germany. Model results are compared with alternative empirical approaches from literature. Results from developing empirical models show that grassland and cropland have to be differentiated according to the key controls driving N2O emissions. N2O emissions of German croplands are highly influenced by climatic conditions and soil properties. The variability of N2O fluxes on grasslands is mainly driven by the fertilizer N applied. The model comparison using measured European N2O emissions exhibits profound discrepancies between the models used on a regional scale. The nationwide budgets derived span a narrow range of −8 to 28% relative to direct N2O emissions quantified by the German national inventory report. The emission factor of German agriculture estimated by the developed model is 0.91% of fertilizer N applied.

On-road emission factor distributions of individual diesel vehicles in and around Beijing, China

Abstract This paper reports findings of a recent field study that characterized the on-road emissions of individual diesel vehicles in and around Beijing, China during November and December of 2009. We successfully sampled 230 individual trucks on 4 major expressways around the city as well as 57 individual buses in the city using refined mobile chasing techniques and fast response instruments. Emission factors (EF) for carbon monoxide (CO), black carbon (BC) and particulate matter with diameters less than 0.5 μm (PM 0.5 ) are derived from the measurements, which are consistent with the results from laboratory dynamometer tests. The PM 0.5 number emission factor distributions demonstrate consistent bimodal modes with peaks around 10 nm and 80 nm, while the mass emission factor distributions demonstrate a unimodal maximum around 110 nm for a majority of the trucks. The BC emissions are shown to be highly correlated with the mass emission of particles with 100–250 nm diameters, which are in good agreement with the results from previous studies. A number of important policy implications are discussed based on the results from this study. First, we identified “heavy emitters” in the on-road fleet we encountered, finding that 5% of diesel trucks in this sample are responsible for 50% of total BC emissions, and 20% of the trucks are responsible for 50% CO and PM 0.5 number emissions, 60% PM 0.5 mass emissions and over 70% of BC emissions. This suggests that emissions control programs should include identifying and removing heavy emitters from the road or improving their emissions. Second, the BC and PM 0.5 number emission factors of trucks registered in regions outside Beijing are significantly higher than those of Beijing-registered trucks, suggesting that improving engine and fuel standards in Beijing alone is not sufficient in reducing the traffic-related air pollution in Beijing. Third, the significantly lower emissions from Euro IV and CNG buses compared to the Euro II and Euro III buses support that introducing clean-burning buses is an effective way to reduce the overall vehicle emissions for the pollutants studied. Fourth, our refined chasing method demonstrates a cost-effective approach to characterize the emissions from a large number of on-road diesel vehicles. Further studies with large sample sizes are critical to constructing more accurate mobile emission inventories to represent the on-road vehicle population.

Evolution of particle number distribution near roadways. Part III: Traffic analysis and on-road size resolved particulate emission factors

On-road size-resolved particulate emission factors were computed using concurrently measured carbon monoxide (CO) as a freeway dilution indicator and correlating roadside particle measurements to CO measurements. The emission factors derived for the total particle number agree well with previous on-road investigations. However, this study extends this analysis to produce unique receptor-dependent, size-resolved, road and grid-level emission factor distributions. Both mileage- and fuel-based particle number and mass emission factors at road and grid levels, along with CO emission factors, are presented and the results from freeways with distinctly different percentages of heavy-duty diesel truck traffic are compared. The effects of plume processing on particle number near roadways are shown to be much more profound than on particle mass, further indicting that the adverse health effects observed near roadways are at least partially related to particle numbers.

Nitrous oxide emission factors for agricultural soils in Great Britain: the impact of soil water‐filled pore space and other controlling variables

AbstractMeasurements were made of nitrous oxide (N2O) emissions from N‐fertilised ungrazed grassland and arable land at sites widely distributed across Great Britain during 1999–2001. The closed static chamber method was used throughout. Emissions varied widely throughout the year at each site, and between sites. Daily fluxes up to 1200 g N2O–N ha−1 d−1 were recorded. The highest annual flux was 27.6 kg N2O–N ha−1 at a grassland site in Wales, whereas the lowest, 1.7 kg N2O–N ha−1, occurred on a soil overlying chalk in southern England. The key factors affecting N2O emissions from agricultural soil were soil WFPS, temperature and soil NO3––N content. On grassland, rainfall (particularly around the time of N application), with its consequent effect on water‐filled pore space (WFPS), was the main driving factor during the growing season. Annual emission factors (EFs), uncorrected for background emission, varied from 0.4 to 6.5% of the nitrogen (N) applied, covering a similar range for grassland to that found previously for sites restricted to Scotland. Continued monitoring at a grassland reference site near Edinburgh showed that annual EFs vary greatly from year to year, even with similar management, and that several years' data are required to produce a robust mean EF. The overall distribution of EFs in this and previous studies was log‐normal. The EFs for small‐grain cereals (and oilseed rape) peaked at a much lower value than those for grassland, whereas the values for leafy vegetables and potato crops fitted well into the grassland distribution. These differences in EF between various types of crop should be taken into account when compiling regional or national N2O emission inventories.

Individual Measurements of the Emission Factor of Aerosol Black Carbon in Automobile Plumes

As automobiles passed a measuring point, we recorded the concentrations of carbon dioxide and aerosol black carbon (BC) in their dispersing exhaust plumes. After subtraction of background levels, the ratio of the increments of these species allows us to calculate the emission factor of BC per unit mass of fuel from each individual vehicle. These factors spanned a range of greater than two orders of magnitude, representing the emission of from 4 × 10−6 to 10−3 grams of aerosol black carbon per gram of carbon consumed in the fuel. Their distribution showed that 20 percent of the vehicles accounted for 65 percent of the emissions. The real-time measurement methodology allows for a determination of the distribution of emission factors across the actual population of sources. These results are similar to the wide range of carbon monoxide emission factors reported recently.