Carbonyls and non-methane hydrocarbons at a rural mountain site in northeastern United States

Measurements of carbonyls and C₂–C₆ non-methane hydrocarbons (NMHCs) were made in ambient air at a rural site at the summit of Whiteface Mountain (WFM) in New York State. Alkanes dominated in the samples, with ethane and propane making up about 55% of the total on a carbon-atom basis. Ethane, the longest-lived of the NMHCs, showed a mixing ratio in the range of 0.86–2.1 ppbv. Photochemical ageing analysis indicated an anthropogenic influence on the NMHC levels. The photochemical reactivity of the hydrocarbons, calculated in terms of propylene-equivalent concentration, was dominated by alkenes (propene and ethene), which accounted for 74% of the total NMHC sum. Air mass back-trajectories have been used to investigate the origin of the observed NMHCs and carbonyls. Higher concentrations were found when air masses arrived from the midwestern US corridor. Acetone was the most abundant species, comprising from 31% to 53% of the total detected carbonyls, followed by MEK (15–53%), HCHO (7–39%), and CH₃CHO (7–19%). Average concentrations were determined to be 1.61 ppbv for CH₃C(O)CH₃, 1.40 ppbv for MEK, 1.16 ppbv for HCHO, and 0.49 ppbv for CH₃CHO. The variations in carbonyl concentrations were observed to follow patterns similar to variations in O₃ concentrations, typical of secondary products. Correlations and statistical analysis of the carbonyls and NMHCs were performed, and showed that most of the compounds derived from mixing and photochemical transformation of long-range transported pollutants from the major source areas. Ranking of the carbonyls with respect to removal of the OH radical showed HCHO to be the most important species, followed by CH₃CHO, MEK, and CH₃C(O)CH₃.     

Spatial and temporal variations in the trace elemental data over the northeastern United States

Time series of trace elemental concentrations (14 species) of atmospheric fine particles measured in the northeastern United States between 1988 and 1998 are analyzed for spatial and temporal variations. The influence of synoptic-scale systems to the transport and accumulation of pollutants can be investigated successfully if the short-term fluctuations (i.e. weather-induced variations) embedded in the time series of pollutant concentrations are separated from the original time series. The spatial short-term correlation coefficients for Al, Br, Fe, Se, and Zn permit good predictions of pollutant concentrations up to distances of about 350 km from a given monitor. The species correlation matrices for individual sites reveal that As, Br, Se, and Zn are highly correlated in New York State, while Fe, Mn, and V show also strong correlations, suggesting the commonality of source regions for these industrial and urban pollutants impacting New York.     

Organic Matter of the Troposphere—II.: Natural Background of biogenic lipid matter in aerosols over the rural western United States

Higher plant waxes are the predominant natural components in the lipid fractions (> C₁₅) of aerosols sampled over rural and oceanic regions. Hydrocarbon, fatty acid, ketone and fatty alcohol fractions of the lipids were characterized in terms of their contents of homologous compound series and specific biogenic molecular markers. Particulate samples from the rural western United States have been analyzed and compared with samples from urban Los Angeles and remote areas over the Atlantic Ocean. The samples from rural sites contained predominantly vascular plant wax and lesser amounts of higher plant sterols and resin residues. Urban samples and, to varying degrees, some rural samples contained primarily higher weight residues of petroleum products. The loadings of hydrocarbons derived from higher plant waxes ranged approximately from 10 to 160 ng m⁻³ of air (for fatty acids, 10–100 ng m⁻³ and for fatty alcohols, 10–200 ng m⁻³). Higher molecular weight lipids (i.e. plant epicuticular wax, terpenes, etc.) from flora comprise a significant component of the organic carbon in rural aerosols. Primary biogenic residues are major components of aerosols in all areas and they are important components in the global cycling of organic carbon.     

Modeled response of ozone to electricity generation emissions in the northeastern United States using three sensitivity techniques

Electrical generation units (EGUs) are important sources of nitrogen oxides (NO_x) that contribute to ozone air pollution. A dynamic management system can anticipate high ozone and dispatch EGU generation on a daily basis to attempt to avoid violations, temporarily scaling back or shutting down EGUs that most influence the high ozone while compensating for that generation elsewhere. Here we investigate the contributions of NO_x from individual EGUs to high daily ozone, with the goal of informing the design of a dynamic management system. In particular, we illustrate the use of three sensitivity techniques in air quality models—brute force, decoupled direct method (DDM), and higher-order DDM—to quantify the sensitivity of high ozone to NO_x emissions from 80 individual EGUs. We model two episodes with high ozone in the region around Pittsburgh, PA, on August 4 and 13, 2005, showing that the contribution of 80 EGUs to 8-hr daily maximum ozone ranges from 1 to >5 ppb at particular locations. At these locations and on the two high ozone days, shutting down power plants roughly 1.5 days before the 8-hr ozone violation causes greater ozone reductions than 1 full day before; however, the benefits of shutting down roughly 2 days before the high ozone are modest compared with 1.5 days. Using DDM, we find that six EGUs are responsible for >65% of the total EGU ozone contribution at locations of interest; in some locations, a single EGU is responsible for most of the contribution. Considering ozone sensitivities for all 80 EGUs, DDM performs well compared with a brute-force simulation with a small normalized mean bias (–0.20), while this bias is reduced when using the higher-order DDM (–0.10).

Implications: Dynamic management of electrical generation has the potential to meet daily ozone air quality standards at low cost. We show that dynamic management can be effective at reducing ozone, as EGU contributions are important and as the number of EGUs that contribute to high ozone in a given location is small (<6). For two high ozone days and seven geographic regions, EGUs would best be shut down or their production scaled back roughly 1.5 days before the forecasted exceedance. Including online sensitivity techniques in an air quality forecasting model can provide timely and useful information on which EGUs would be most beneficial to shut down or scale back temporarily.     

Quantifying flexibility in combating climate change: modelling the implications of flexibility mechanisms in the climate change negotiations

With the 'International Trading of Emission Allowances' (ITEA) model, we have analysed the flexibility mechanisms provided for in the Kyoto Protocol. Three main mechanisms of flexibility are analysed differentiation of initial commitments, multiple sources, and locational flexibility (trading). A differentiation of commitments could help the evolution of commitments, especially with a trading regime, which could create some income. Multiple sources give a large pool of cheaper abatement options from the non-CO₂ gases, and costs are reduced substantially. Finally, a trading regime would make available even more cheap abatement options, mainly in the economies in transition (EITs). This regime would provide income support for the EITs, helping them to speed up their transition. The combined mechanisms reduce dramatically the costs for the compliance with the protocol for the whole of Annex I; they fall to zero in some cases. Two other main findings deal with the EU and the EITs. Internal trading would ease the debate on the internal distribution of commitments within the EU under the bubble provision, reducing costs significantly. The allocations in the protocol for the EITs probably create a huge excess - 'hot air' - which could seriously harm the agreement if it is not dealt with. Excluding the hot air will increase costs for the quota importers, and it will also slightly reduce income for the relevant EITs, but this is offset by a rising price, which also benefits other EITs.     

Assessment of secondary organic carbon in the Southeastern United States: a review

Organic carbon (OC) is one of the major components of ambient PM2.5 (particulate matter [PM] < or = 2.5 microm in aerodynamic diameter) and a significant portion of OC is from secondary organic aerosol (SOA) formation in the southeastern United States. Various approaches (based on measurement and modeling results) are applied to estimate secondary organic carbon (SOC) and its origins in the region. SOC estimates by various methods are consistent as to clear seasonal variation (i.e., relatively higher SOC in summer) and little spatial variability (i.e., a regional characteristic of SOC). However, there are differences as to the origins of SOC. SOA organic tracer and emission-based modeling studies indicate that the biogenic origin of SOC is dominant in the Southeast, showing that biogenic-origin SOC accounts for 90% of SOC in summer and more than 70% even in other seasons. However, results from other studies suggest that the anthropogenic origin of SOC is dominant, significant amounts of anthropogenic-origin SOC, or important roles of anthropogenic pollutants for SOA formation, especially at urban areas, as strong correlations between water-soluble OC (an indicator of SOC) and anthropogenic pollutants, considerable amounts of fossil water-soluble OC, and significant contributions of fossil SOC (37-52% in summer months, 70-73% in winter months) are observed. Therefore, more studies are needed to reconcile the differences in the source attribution of SOC measurements.     

ATR-FTIR characterization of organic functional groups and inorganic ions in ambient aerosols at a rural site

An Attenuated Total Reflectance-Fourier Transform Infrared (ATR-FTIR) spectroscopic method was used to measure organic functional groups and inorganic ions at Tonto National Monument (TNM), an Interagency Monitoring of Protected Visual Environments (IMPROVE) sampling site in a rural area near Phoenix, Arizona. Functional groups and ions from common aerosol compound classes such as aliphatic and aromatic CH, methylene, methyl, aldehydes/ketones, carboxylic acids, ammonium sulfate and nitrate as well as functional groups from difficult to measure compound classes such as esters/lactones, acid anhydrides, carbohydrate hydroxyl and ethers, amino acids, and amines were quantified. On average, ～33% of the PM_1.0 mass was composed of organic aerosol. The average (standard deviation) composition of the organic aerosol at TNM was 34% (6%) biogenic functional groups, 21% (5%) oxygenated functional groups, 28% (7%) aliphatic hydrocarbon functional groups (aliphatic CH, methylene and methyl) and 17% (1%) aromatic hydrocarbon functional groups. Compositional analysis, functional group correlations, and back trajectories were used to identify three types of events with source signatures: primary biogenic-influenced, urban-influenced, and regional background. The biogenic-influenced event had high concentrations of amino acids and carbohydrate hydroxyl and ether, as well as aliphatic CH and aromatic CH functional groups and qualitatively high levels of silicate. The urban-influenced events had back trajectories traveling directly from the Phoenix area and high concentrations of hydrocarbons, oxygenated functional groups, and inorganic ions. This aerosol characterization suggests that both primary emissions in Phoenix and secondary formation of aerosols from Phoenix emissions had a major impact on the aerosol composition and concentration at TNM. The regional background source had low concentrations of all functional groups, but had higher concentrations of biogenic functional groups than the urban source.     

Spatial distribution of source locations for particulate nitrate and sulfate in the upper-midwestern United States

Two back-trajectory analysis methods designed to be used with multiple site data, simplified quantitative transport bias analysis (SQTBA) and residence time weighted concentration (RTWC), were applied to nitrate and sulfate concentration data from two rural sites (the Mammoth Cave National Park and the Great Smoky Mountain National Park) and five urban sites (Chicago, Cleveland, Detroit, Indianapolis, and St. Louis) for an intensive investigation on the spatial patterns of origins for these two species in the upper-midwestern area. The study was made by dividing the data into five categories: all sites and all seasons, rural sites in summer, rural sites in winter, urban sites in summer, and urban sites in winter. A general conclusion was that the origins of the nitrate in these seven sites were mainly in the upper-midwestern areas, while the sulfate in these seven sites were mainly from the Ohio and Tennessee River Valley areas. The upper-midwestern areas are regions of high ammonia emissions rather than high NO_x emissions. In the winter, metropolitan areas showed the highest nitrate emission potential suggesting the importance of local NO_x emissions. In the summer, ammonia emissions from fertilizer application in the lower midwestern area made a significant contribution to nitrate in the rural sites of this study. The impact of the wind direction prevalence on the source spatial patterns was observed by comparing the urban and rural patterns of the summer. The differences between the results of two methods are discussed and suggestions for applying these methods are also provided.     

Correlations between fine particulate matter (PM2.5) and meteorological variables in the United States: Implications for the sensitivity of PM2.5 to climate change

We applied a multiple linear regression (MLR) model to study the correlations of total PM_2.5 and its components with meteorological variables using an 11-year (1998–2008) observational record over the contiguous US. The data were deseasonalized and detrended to focus on synoptic-scale correlations. We find that daily variation in meteorology as described by the MLR can explain up to 50% of PM_2.5 variability with temperature, relative humidity (RH), precipitation, and circulation all being important predictors. Temperature is positively correlated with sulfate, organic carbon (OC) and elemental carbon (EC) almost everywhere. The correlation of nitrate with temperature is negative in the Southeast but positive in California and the Great Plains. RH is positively correlated with sulfate and nitrate, but negatively with OC and EC. Precipitation is strongly negatively correlated with all PM_2.5 components. We find that PM_2.5 concentrations are on average 2.6 μg m^?3 higher on stagnant vs. non-stagnant days. Our observed correlations provide a test for chemical transport models used to simulate the sensitivity of PM_2.5 to climate change. They point to the importance of adequately representing the temperature dependence of agricultural, biogenic and wildfire emissions in these models.     

Spatial and temporal distributions of airborne sulfate in parts of the United States

The current knowledge of the spatial and temporal distribution of airborne, water soluble sulfate is surveyed for two “scales” of atmospheric activity. The “urban” scale with episodes extending over a day or two over distances of about 100 km is illustrated for two comparable American cities, Los Angeles and New York. The regional scale with episodes extending up to several days over distances of 1000 km is exemplified by case studies in the greater eastern United States. Examination of available data reveals several features of the spatial and temporal variation in sulfate occurrence, including seasonal changes, and correlations with aerometric parameters. The importance of water vapor and air mass character on sulfate concentrations is assessed in both the urban and regional conditions. The results of initial attempts to simulate the impact of sulfur oxide emissions on ambient sulfate distributions are compared with an episode case extending over several days in July 1974.     

Measurement of black carbon aerosols near two Chinese megacities and the implications for improving emission inventories

Knowledge of the distribution and sources of black carbon (BC) is essential to understanding its impact on radiative forcing and the establishment of a control strategy. In this study, we analyze atmospheric BC and its relationships with fine particles (PM_2.5) and trace gases (CO, NO_y and SO₂) measured in the summer of 2005 in two areas frequently influenced by plumes from Beijing and Shanghai, the two largest cities in China. The results revealed different BC source characteristics for the two megacities. The average concentration of BC was 2.37 (±1.79) and 5.47 (±4.00) μg m^?3, accounting for 3.1% and 7.8% of the PM_2.5 mass, in Beijing and Shanghai, respectively. The good correlation between BC, CO and NO_y (R² = 0.54–0.77) and the poor correlation between BC and SO₂ suggest that diesel vehicles and marine vessels are the dominant sources of BC in the two urban areas during summer. The BC/CO mass ratio in the air mass from Shanghai was found to be much higher than that in the air mass from Beijing (0.0101 versus 0.0037 ΔgBC/ΔgCO), which is attributable to a larger contribution from diesel burning (diesel-powered vehicles and marine vessels) in Shanghai. Based on the measured ratios of BC/CO and annual emissions of CO, we estimate that the annual emissions of BC in Beijing and Shanghai are 9.51 Gg and 18.72 Gg, respectively. The improved emission rates of BC will help reduce the uncertainty in the assessment of the impact of megacities on regional climate.     

Spatial variability of carbonaceous aerosols and associated source tracers in two cites in the Midwestern United States

Semi-continuous and 24-h averaged measurements of fine carbonaceous aerosols were made concurrently at three sites within each of two U.S. Midwestern Cities; Detroit, Michigan and Cleveland, Ohio; during two, one-month intensive campaigns conducted in July of 2007 and January & February of 2008. A comparison of 24-h measurements revealed substantial intra-urban variability in carbonaceous aerosols consistent with the influence of local sources, and excesses in both PM_2.5 organic carbon (OC) and elemental carbon (EC) were identified at individual sites within each city. High time-resolved black carbon (BC) measurements indicated that elemental carbon concentrations were higher at sites adjacent to freeways and busy surface streets, and temporal patterns suggested that excess EC at sites adjacent to freeways was dominated by mobile source emissions while excesses in EC away from traffic corridors was dominated by point/area source emissions. The site-to-site variability in OC concentrations was approximately 7% within the neighborhood scale (0.5–4 km) and between 4 and 27% at the urban scale (4–100 km). In contrast, measurements of organic source tracers, in conjunction with a Chemical Mass Balance (CMB) source-apportionment model, indicated that the spatial variation in the contribution of both mobile and stationary sources to PM_2.5 OC often exceeded the variation in OC mass concentration by a factor of 3 or more. Markers for mobile sources, biomass smoke, natural gas, and coal combustion differed by as much as 60% within the neighborhood scale and by greater than 200% within the urban scale. The observations made during this study suggest that the urban excess of carbonaceous aerosols is much more complex than has been previously reported and that a more rigorous, source-oriented approach should be taken in order to assess the risk associated with exposure to carbonaceous aerosols within the industrialized environments of the Midwestern United States.     

Summer and winter nonmethane hydrocarbon emissions from on-road motor vehicles in the Midwestern United States

On-road vehicle emission rates of nonmethane hydrocarbons (NMHCs) were measured in two tunnels in Milwaukee, WI, in summer 2000 and winter 2001. Seasonal ambient temperatures in the Midwestern United States vary more widely than in locations where most studies of NMHC emissions from vehicle fleets have been conducted. Ethanol is the added fuel oxygenate in the area, and, thus, emissions measured here are of interest as other regions phase out methyl tertiary butyl ether and increase the use of ethanol. Total emissions of NMHCs in three types of tunnel tests averaged 4560 +/- 800 mg L(-1) fuel burned (average +/- standard error). To investigate the impact of cold start on vehicle emissions, samples were collected as vehicles exited a parking structure in subzero temperatures. NMHC emissions in the subzero cold-start test were 8830 +/- 190 mg L(-1) fuel-nearly double the tunnel emissions. Comparison of ambient data for the Milwaukee area with tunnel emissions showed the impact of seasonal differences in fuels and emissions on the urban atmosphere. Composition of fuel samples collected from area gas stations in both seasons was correlated with vehicle emissions; the predominant difference was increased winter emissions of lighter hydrocarbons present in winter gasoline. A chemical mass balance model was used to determine the contributions of whole gasoline and gasoline headspace vapors to vehicle emissions in the tunnel and cold-start tests, which were found to vary with season. Results of the mass balance model also indicate that partially combusted components of gasoline are a major contributor to emissions of aromatic compounds and air toxic compounds, including benzene, toluene, xylenes, napthalene, and 1,3-butadiene, whereas air toxics hexane and 2,2,4-trimethylpentane are largely attributed to gasoline and headspace vapors.     

Orchard management under the effects of climate change: implications for apple,plum, and almond growing

Environmental Science and Pollution Research - The authors analyzed certain species and varieties of fruit tree in which applied crop technology is used and also undergoes the effects of climate...     

Black carbon and polycyclic aromatic hydrocarbon emissions from vehicles in the United States-Mexico border region: pilot study

The investigators developed a system to measure black carbon (BC) and particle-bound polycyclic aromatic hydrocarbon (PAH) emission factors during roadside sampling in four cities along the United States-Mexico border, Calexico/Mexicali and El Paso/Juarez. The measurement system included a photoacoustic analyzer for BC, a photoelectric aerosol sensor for particle-bound PAHs, and a carbon dioxide (CO2) analyzer. When a vehicle with measurable emissions passed the system probe, corresponding BC, PAH, and CO2 peaks were evident, and a fuel-based emission factor was estimated. A picture of each vehicle was also recorded with a digital camera. The advantage of this system, compared with other roadside methods, is the direct measurement of particulate matter components and limited interference from roadside dust. The study revealed some interesting trends: Mexican buses and all medium-duty trucks were more frequently identified as high emitters of BC and PAH than heavy-duty trucks or passenger vehicles. In addition, because of the high daily mileage of buses, they are good candidates for additional study. Mexican trucks and buses had higher average emission factors compared with U.S. trucks and buses, but the differences were not statistically significant. Few passenger vehicles had measurable BC and PAH emissions, although the highest emission factor came from an older model passenger vehicle licensed in Baja California.     

Knowledge domain and emerging trends of carbon footprint in the field of climate change and energy use: a bibliometric analysis

Carbon footprint (CF) research has attained tremendous popularity for improving the climate environment purposes. In particular, current energy use has been identified as the main cause of climate change. CF plays an irreplaceable role in managing energy use, reducing gas emissions, and improving climate change. The objective of this study was to review studies that have developed CF and to perform a bibliometric analysis using two key terms: “climate change” and “energy use”. From bibliometric analysis using CiteSpace and VOSviewer, it was possible to establish a knowledge map of cooperative network structure and research evolution. We are aiming to reveal the main logical chain of CF research leading to climate change, to make up for the lack of current literature, and provide research inspiration for researchers. The research findings mainly focus on four aspects. First, the relevant research began in 2008 and is in a state of continuous rise. Second, due to the law of research development and the prominence of practical problems, related research has experienced a stage from conceptual methods to specific problems. Third, China and the USA assume an important role in which international cooperation is the overall trend. Fourth, related research can be divided into CF algorithm research, ecological environment management research, and specific cross-industry fields. In addition, possible opportunities for change in related research are explored. It is also suggested that the integration of CF with other footprints, when energy use and environmental change are fully considered, may become an important future research trend by providing a more comprehensive environmental impact.

     

Comparison of fine particles and the relationship between particle variations and meteorology at an urban site and a remote site in the Eastern United States

This study compared the variations in the mass of certain particles at an urban site, Washington, DC, and at a remote site, Shenandoah National Park, VA, in the eastern United States. Seven years (1991-1997) of Interagency Monitoring of Protected Visual Environments (IMPROVE) fine particulate matter (PM2.5), PM10, coarse fraction, SO4(2-), and total sulfur data were used for this study together with available meteorology/climatology data. Various statistical modeling and analysis procedures, including time series analysis, factor analysis, and regression modeling, were employed. Time series of the constituents were divided into four terms: the long-term mean, the intraannual perturbation, the interannual perturbation, and the synoptic perturbation. PM2.5 at the two sites made up approximately 72% of the total mass for PM10, and the coarse fraction made up the remaining 28%, on average. Thirty-one percent of the PM2.5 at the DC site and 42% at the Shenandoah site was SO4(2-), based on average data for the entire period. At the DC site, the two main contributors to the constituent mass were the long-term mean and the synoptic perturbation terms, and at the Shenandoah site, they were the long-term mean and the intra-annual perturbation terms. This suggested that the constituent mass at the two sites was affected by very different processes. The terms that provided the principal contribution to the constituent mass at the two sites were studied in detail. At the DC site, dew point trends, a climate variable, were the primary driver of the 7-year trends for PM2.5, PM10, the coarse fraction, and total sulfur, and SO2 emission trends were the primary driver of the trends for SO4(2-). SO2 emission trends influenced the trends for PM2.5 and total sulfur, appearing as the second term in the model, but only parameters dealing with climate trends had significant effects on the trends for PM10 and the coarse fraction. At the Shenandoah site, only parameters dealing with climate trends affected long-term particle trends.     

Assessment of the Nested Grid Model Estimates for Driving Regional Visibility Models in the Southwestern United States

ABSTRACT

The Nested Grid Model (NGM) is a primitive-equation meteorological model that is routinely exercised over North America for forecasting purposes by the National Meteorological Center. While prognostic meteorological models are being increasingly used to drive air quality models, their use in conducting annual simulations requires significant resources. NGM estimates of wind fields and other meteorological variables provide an attractive alternative since they are typically archived and readily available for an entire year. Preliminary evaluation of NGM winds during the summer of 1992 for application to the region surrounding the Grand Canyon National Park showed serious shortcomings. The NGM winds along the borders between California, Arizona and Mexico tend to be northwesterly with a speed of about 6 m/sec, while the observed flow is predominantly southerly at about 2-5 m/sec. The mesoscale effect of a thermal low pressure area over the highly heated Southern California and western Arizona deserts does not appear to be represented by the NGM because of its coarse resolution and the use of sparse observations in that region. Tracer simulations and statistical evaluation against special high resolution observations of winds in the southwest United States clearly demonstrate the northwest bias in NGM winds and its adverse effect on predictions of an air quality model. The “enhanced” NGM winds, in which selected wind observations are incorporated in the NGM winds using a diagnostic meteorological model provide additional confirmation on the primary cause of the northwest bias. This study has demonstrated that in situations where limited resources prevent the use of prognostic meteorological models, previously archived coarse resolution wind fields in which additional observations are incorporated to correct known biases provide an attractive option.     

Remote sensing-based estimates of annual and seasonal emissions from crop residue burning in the contiguous United States

Crop residue burning is an extensive agricultural practice in the contiguous United States (CONUS). This analysis presents the results of a remote sensing-based study of crop residue burning emissions in the CONUS for the time period 2003-2007 for the atmospheric species of carbon dioxide (CO2), methane (CH4), carbon monoxide (CO), nitrogen dioxide (NO2, sulfur dioxide (SO2), PM2.5 (particulate matter [PM] < or = 2.5 microm in aerodynamic diameter), and PM10 (PM < or = 10 microm in aerodynamic diameter). Cropland burned area and associated crop types were derived from Moderate Resolution Imaging Spectroradiometer (MODIS) products. Emission factors, fuel load, and combustion completeness estimates were derived from the scientific literature, governmental reports, and expert knowledge. Emissions were calculated using the bottom-up approach in which emissions are the product of burned area, fuel load, and combustion completeness for each specific crop type. On average, annual crop residue burning in the CONUS emitted 6.1 Tg of CO2, 8.9 Gg of CH4, 232.4 Gg of CO, 10.6 Gg of NO2, 4.4 Gg of SO2, 20.9 Gg of PM2.5, and 28.5 Gg of PM10. These emissions remained fairly consistent, with an average interannual variability of crop residue burning emissions of +/- 10%. The states with the highest emissions were Arkansas, California, Florida, Idaho, Texas, and Washington. Most emissions were clustered in the southeastern United States, the Great Plains, and the Pacific Northwest. Air quality and carbon emissions were concentrated in the spring, summer, and fall, with an exception because of winter harvesting of sugarcane in Florida, Louisiana, and Texas. Sugarcane, wheat, and rice residues accounted for approximately 70% of all crop residue burning and associated emissions. Estimates of CO and CH4 from agricultural waste burning by the U.S. Environmental Protection Agency were 73 and 78% higher than the CO and CH4 emission estimates from this analysis, respectively. This analysis also showed that crop residue burning emissions are a minor source of CH4 emissions (< 1%) compared with the CH4 emissions from other agricultural sources, specifically enteric fermentation, manure management, and rice cultivation.     

An evaluation of the UAM-V predicted concentrations of carbon monoxide and reactive nitrogen compounds over the eastern United States during summer 1995

While there is a clear need to evaluate a photochemical model's ability in predicting not only the concentrations of O3, but also precursors and other trace species, many previous studies have focused only on the assessment of During the 1995 summer season, in addition to the routine monitoring of criteria pollutants, several research-oriented monitoring campaigns were conducted over the eastern United States, providing an extensive database of reactive nitrogen compounds, CO, and speciated hydrocarbon data. In this study, we examine the ability of a photochemical modeling system, RAMS/ UAM-V, to reproduce the measured concentrations of CO, NO2, and NOy over the region during the summer of 1995. The results demonstrate that there is agreement between modeled and measured seasonal average concentrations of NO2, both at the routine and research monitors. The same is true for NOy, but to a lesser degree. However, the model is found to significantly underpredict CO for the routine monitors in comparison to the research monitors.