Inventory and Characterization of Emissions

This report was written in 2012 as a part of the Bi-national Air Quality Project. Highlights that are of interest to the public are reported below. Read the full report here.

This report summarizes a survey of inventories of land-based air pollutant sources. Air pollution emission source categories in this region include:

  • major point sources (e.g., power stations, incinerators, cement plants, and steam generators)
  • area sources (e.g., fires, wind-blown dust, cooking, and residential fuel combustion)
  • mobile sources (e.g., cars, trucks, off-road heavy equipment, trains, and aircraft)
  • agricultural and ranching activities(e.g., fertilizers, tilling and harvesting operations and ammonia emissions from livestock)
  • biogenic sources (e.g., oxides of nitrogen from biological activity in soils and hydrocarbon emissions from plants)

Road dust from unpaved and paved roads constitutes one of the most important sources of PM10 (particulate matter with a diameter equal to or less than 10 micrometers) and PM2.5 (particulate matter with a diameter of less than 2.5 micrometers) in the Paso del Norte and across the study region. A recent emission inventory for Cd. Juárez estimated 26% of the annual PM2.5 emissions came from unpaved roads (PNEG, 2003). In Ciudad Juárez and in other rural areas, unpaved road dust is a critical health and nuisance issue since many busy urban roads are unpaved and paving has not kept up with the population growth. In Cd. Juárez, approximately half a million vehicles (passenger cars and trucks) are registered in the city, with nearly 50,000 vehicles crossing the U.S.-Mexican border into El Paso each day (US BTS, 2009).

Dust emissions from agricultural activities are expected to be the greatest between January and March when major land preparation activities occur in the Mesilla Valley and areas south of El Paso on both sides of the border. Unpaved road dust can be a significant contributor to the overall particulate matter emission inventory, especially during agricultural harvests when vehicles travel down the numerous farm roads. Most urban roads are paved, but in many small settlements, or colonias, the majority of roads are unpaved with little or no dust control.

Particulates from combustion sources have been detected at urban and non-urban receptors throughout the year, but they are most abundant during the wintertime holiday season at urban sites. Particulates from residential heating account for as much as 44% of the annual PM2.5 in Cd. Juárez. Small space heaters are widely used in Cd. Juárez in the cool months in homes without central heating. Some of these heaters are fueled by propane, but many are still fueled with wood or other combustibles, which can include refuse. As much as 60% of the lower income family houses use an unvented gas space heater or wood burning heater (Graham et al., 2004, 2005). As in many areas in the west, spatially dense monitoring studies have shown that the residential wood smoke contributions are more variable in space than motor vehicle exhaust emissions, with much higher contributions in residential neighborhoods than in commercial districts just a few kilometers away.

Atmospheric oxidation reactions of nitrogen oxides (NO + NO2 = NOx), sulfur dioxide (SO2), and volatile organic compounds (VOCs) during winter contribute to the formation of condensable nitrate (NO3-), sulfate (SO42-), and organic compounds that, under certain meteorological conditions, favor the formation of new particles with aerodynamic diameters less than 2.5 micrometers. On-road and non-road mobile sources are a significant source of NOx in the Paso del Norte air basin. Sulfur dioxide and oxides of nitrogen emissions are most intense along the major roadways, as well as in population centers where many vehicle miles are logged each day. Particulate matter emissions are largest in the population centers and are minor at the point source locations.

Point Source Emissions

New Mexico Point Source Inventory

The NMED Air Quality Bureau emissions inventory database is the primary source of atmospheric point source pollutant emissions in New Mexico. The AQB is responsible for the management and dissemination of this database. This is New Mexico’s regulatory emission inventory that provides detailed historical point source records for PM10, PM2.5, TSP, NOx, CO, CO2, NH3, SO2, total VOC, and the 188 listed federal hazardous air pollutants and state toxic air pollutants. The point source emission inventory exists at the facility level providing allowable annual emissions. Approximately 300 companies and 805 facilities are included in the 2002 inventory. Actual annual emissions exist for the major sources measuring over 100 tons per year. Major point sources of NOx in the study area in New Mexico include the El Paso Electric Rio Grande Generating Station at Sunland Park, the Luna Energy Facility near Deming, the PNM Lordsburg Generating Station and the PNM Afton Generating Station west of La Mesa.

Texas Point Source Inventory

The TCEQ collects information about air pollutants emitted from industrial point sources in Texas that is stored in the State of Texas Air Reporting System (STARS). Only those sites whose emission rates exceed the reporting applicability levels found in 30 Texas Administrative Code 101.10. Table 1 shows a listing of the point sources in El Paso County with emissions in tons per year. The top NOx emitter in the county is the Newman Generating Station in northern El Paso County. The Copper Station is another natural gas electrical generating station located in El Paso and is used as a peaking station.

Table of point source emissions in El Paso County, 2009
Table 1. Point Sources in El Paso County from the 2009 National Emissions Inventory

Arizona Point Source Inventory

The Arizona Department of Environmental Quality (ADEQ) collects information about air pollutants emitted from industrial point sources in Arizona. For this study, counties in southeast Arizona were considered. The largest point source of NOx in the area in Arizona is the Apache Station Power Plant. This station is located in Cochise County approximately 13 kilometers south of interstate 10 on highway 191.

Mexico Point Source Inventory

We looked at The Mexican National Emission Inventory for this study. We looked at the area of northern Chihuahua that is part of the study area. We have noticed that 37 of the 748 records had the same latitude/longitude value in the central business district of Cd. Juárez. A significant portion of the point source emissions are located at the Samalayuca power plant facility 42 kilometers south of Cd Juárez owned by state utility Comisión Federal de Electricidad (CFE).

Area Source Inventory

Agricultural Emissions

Agricultural activities and lands emit not only particulates but also gaseous pollutants. Dust emissions in the agricultural valleys are expected to be the greatest between January and March when major land preparation activities occur in the Mesilla and Rincon Valleys. Emissions from confined animal feeding operations include gaseous methane, ammonia, hydrogen sulfide, as well as dust from unpaved roads and wind erosion.

Fugitive Dust Emissions

Dust emissions are moderate during summer when surface winds are sluggish with many agricultural fields covered in vegetation. So-called not inventoried area sources, such as rock quarries, construction, open burning and agricultural tilling are not specifically included in the existing emissions inventory. Figure 1 shows the locations of some of these sources based on digital land use data, aerial photo interpretation and tabular data from annual reports (EMNRD, 2001; Orris, 2000; Pfeil, 2001).

Map of fugitive dust emissions of the NM border region
Figure 1. Locations of Historical Area Dust Sources

Unpaved Road Dust

Other major categories of fugitive PM include road dust and wind erosion. Unpaved road dust can be a significant contributor to the overall PM, especially during agricultural harvests when vehicles travel down the numerous farm roads. Most urban roads are paved but many small settlements, or colonias, have unpaved roads with little or no dust control.

Large dust plumes from dirt roads in the peripheral areas of Cd. Juárez can also be seen during period of low winds. When traveling through the western part of the city one can notice public transportation buses generating large dust plumes. An excellent observation point for the Paso del Norte air shed is from the top of Ranger Peak at the ridge of the Franklin Mountains. In the afternoon, dust plumes from the main road that leads into Anapra can be seen regularly.

Wind-Blown Dust Emissions

Wind-blown dust emissions from both natural and anthropogenic sources often dominate the total PM10 and PM2.5 mass measured in the region. Wind-blown dust sources tend to be highly localized in many cases depending on the erodibility and wind gusts. The Chihuahuan desert is one of several highly erodible areas of the North America, with documentation on dust storms since the early settlers in the 1800s.

Overall, fugitive dust emissions are lowest during summer when surfaces are moist from the monsoons. However, during drought conditions, the monsoon season may bring many thunderstorms with little to no rain, high winds, and consequently, wind-blown dust. Dust emissions increase during late spring when ground surfaces are dry and frontal passages create windy conditions with patchy precipitation.

There are numerous natural sources of PM in the study region. One of the most significant natural sources of PM is found on the approximately 275 square mile gypsum dune area located within the Tularosa Basin. The dunes are within the boundaries of the White Sands National Monument and White Sands Missile Range.

Prospero et al. (2002) mapped out sources of wind-blown soil dust in northern Mexico that regularly impact New Mexico and west Texas based on observations of the TOMS absorbing aerosol product. They mention three large playas that are presently active emitters of dust: Bolson de los Muertos, Laguna Guzman and Medanos de Samalayuca. Figure 2 shows the locations of these three playas as well as other large ones. Additional large dry lakes in Mexico include Laguna Santa Maria, Laguna los Moscos, Laguna Polvaredones, Laguna los Juguetes and La Soda Playa. The Cloverdale dry lake is located approximately 50 kilometers southwest of the now closed NMED Goldhill PM10 monitoring site.

Map of dust source areas in the NM border region
Figure 2. Dust Source Areas

North and South Alkali Flats are problematic for drivers on Interstate 10 west of Lordsburg when winds are high. In fact, many traffic fatalities have occurred during these events. In many cases these playas fill with water in the winter and summer and as they evaporate they become a reservoir for dust.

Mobile Source Emissions

Mobile sources include those that drive on the road (on-road) and those that are not licensed (off-road) to be on the road and those that can be moved and are not stationary. Off-road also includes construction vehicles, airplanes, and small motor driven equipment such as generators, gardening equipment, and lawn mowers. The Paso del Norte air basin is the most significant source of motor vehicle NOx and PM in southern New Mexico. Carbon monoxide, ultrafine particulates, and oxides of nitrogen emissions are most intense along the major roadways, as well as in population centers where many vehicle miles are logged each day.

Biomass Burning Emissions

This source category represents anthropogenic and natural sources across the region. Anthropogenic sources include residential wood burning, agricultural burning, and wood pile and prescribed burning. Wildfires are an example of natural sources even though they may have been human caused.

Biogenic Emissions

Biogenic hydrocarbon emissions from crops and uninhabited regions in the southern New Mexico study area are anticipated to be low because of sparse vegetation and little precipitation. Hot spot ammonia emissions are concentrated around the livestock feedlots along the Mesilla Valley. Some of the emissions, such as field burning and wildfires, are intermittent and local, and the annualized tons per day estimate does not reflect the degree to which they may have been contributors to ambient pollutant levels for the few days on which these activities took place.

Biogenic emissions result from natural biological processes, such as the decomposition or combustion of vegetative matter. Biogenic emissions are part of a closed carbon loop. Examples of biogenic emission sources include burning vegetation (biomass) to produce electricity or using plant-based biofuels for transport. Specifically, the emissions refer to emissions of volatile organic compounds from vegetation, emissions of nitrogen oxides from soil, terpenes, methane, and CO. For example, here are the relative contribution for each county of VOCs: Cochise, Graham, and Otero emit the highest VOCs, while El Paso and Greenlee counties emit the least.

References

ENMRD (2001). Annual Report. New Mexico Energy, Minerals and Natural Resources Department, 2001.

Graham, J.P., P.L. Gurian, V. Corella-Barud, and R. Avilla. (2004). Peri-urbanization and in-home environmental health risks: the side effects of planned and unplanned growth. Int J Hyg Environ Health. 2004; 207(5):447–54.

Graham, J.P., V. Corella-Barud, R. Avitia-Diaz and P. Gurian. (2005). The in-home environment and household health: A cross-sectional study of informal urban settlements in Northern Mexico, Int. J. Env. Res. and Public Health. 2005; 2(3): 394-402.

Orris, G.J. (2000). New Mexico aggregate production sites, 1997-1999. USGS Open-File Report 00-011-A. Prepared by USGS.

Pfeil, J. (2001). New Mexico's natural resources 2001. Prepared by Energy, Minerals and Natural Resources Department, Santa Fe, NM.

PNEG (2003). Development of GIS-based Maps for the Ciudad Juárez Area Source Emissions Inventory Project. Prepared for the Texas Commission on Environmental Quality. Prepared by the Texas Commission on Environmental Quality. Prepared by the Paso del Norte Environmental Group, El Paso, Texas. August 24.

Prospero, J.M., P. Ginoux, O. Torres, S. Nicholson, and T. Gill, Environmental Characterization of Global Sources of Atmospheric Soil Dust Identified with the NIMBUS7 Total Ozone Mapping Spectrometer (TOMS) Absorbing Aerosol Product, Rev. Geophys., 40 (1).

US Bureau of Transportation Statistics (BTS), U.S. Border Crossings/ Entries by State/Port and Month/Year Sorted by Year. 2009, http://www.transtats.bts.gov/BorderCrossing.aspx