Air Quality Assessment Report

An air quality assessment report for the binational Paso del Norte region was written by project team members in fiscal year 2012 (FY12). Some highlights are reported here. Complex terrain, topography, meteorology and emission sources play an important role in determining the impact of pollution on air quality in the study area. The varied landscape includes highly urbanized and rural areas in the Chihuahuan Desert, Rio Grande River Valley, and four mountain ranges (Gila, Organ, Franklin, and Sierra Juárez). Large emission sources include natural desert lands, motor vehicles, manufacturing, various industrial sectors, power plants, and paved and unpaved roads. Smaller emission sources, impacting localized areas, include mining, agriculture and land development. Meteorological conditions create strong winds and blowing dust throughout the region in the winter and spring months (November-May). Atmospheric inversions and calm winds do not allow vertical or horizontal mixing, trapping pollutants near the surface, increasing concentrations of particulate matter. In summer, plentiful sunshine provides the light necessary to drive ozone formation in the more urbanized areas and thunderstorm outflow during the monsoon season can cause localized blowing dust.

Image of geographic region of air quality assessment

Regulation

The United States Environmental Protection Agency (EPA) sets National Ambient Air Quality Standards (NAAQS) for six criteria air pollutants (CAPs). These six pollutants are carbon monoxide, lead, nitrogen dioxide, ozone, particulate pollution, and sulfur dioxide. Federal law requires EPA to review each NAAQS on a five-year schedule to determine the adequacy of each standard to protect public health in light of new research, technology, and existing emission reduction programs. When an area does not meet a NAAQS, the EPA designates it as nonattainment, which triggers planning, emission reduction, and monitoring requirements. Currently, a small portion of Doña Ana County (Anthony, NM) and all of El Paso County are designated as nonattainment for particulate matter sets National Ambient Air Quality Standards (NAAQS) for six criteria air pollutants (CAPs). These six pollutants are carbon monoxide, lead, nitrogen dioxide, ozone, particulate pollution, and sulfur dioxide. Federal law requires EPA to review each NAAQS on a five-year schedule to determine the adequacy of each standard to protect public health in light of new research, technology, and existing emission reduction programs. When an area does not meet a NAAQS, the EPA designates it as nonattainment, which triggers planning, emission reduction, and monitoring requirements. Currently, a small portion of Doña Ana County (Anthony, NM) and all of El Paso County are designated as nonattainment for particulate matter with an aerodynamic diameter of 10 micrometers or less (PM10). With the implementation of the 8-hour ozone NAAQS in 1997, the 1-hour ozone nonattainment areas in Doña Ana and El Paso Counties were re-designated to attainment with requirements to maintain the standard (maintenance status) for a period of ten years. In 1991 the city of El Paso was designated as nonattainment for the 8-hour Carbon Monoxide (CO) NAAQS. By 2003 El Paso attained the CO standard and a maintenance plan was approved by EPA in 2008.) with an aerodynamic diameter of 10 micrometers or less (PM10). With the implementation of the 8-hour ozone NAAQS in 1997, the 1-hour ozone nonattainment areas in Doña Ana and El Paso Counties were re-designated to attainment with requirements to maintain the standard (maintenance status) for a period of ten years. In 1991 the city of El Paso was designated as nonattainment for the 8-hour Carbon Monoxide (CO) NAAQS. By 2003 El Paso attained the CO standard and a maintenance plan was approved by EPA in 2008.

The Impact of Wildfires on Ozone Concentration

The air quality assessment report was divided into four sections. The first section was devoted to an assessment of ozone (O3 ) and the effect wildfires have on concentrations of it in the region. In this study the annual trends and patterns of time and location of 8-hr maximum O3 concentrations in the Paso del Norte region were analyzed and their associations with fires were examined. O3 measurements were retrieved from EPA’s Air Quality System (AQS), while the times and locations of fires were acquired from USDA’s MODIS fire detection module. Time series analysis of deseasonalized O3 levels showed statistically significant declining trends for most of the sites located in populated areas and high correlation coefficients among each other due to reductions of NOx (oxides of nitrogen) emissions . A 0.12 ppbv/yr increase of 8-hr O3 concentration was computed for Chiricahua in Arizona, a background site located in a Class I protected area, while moderate correlations with the urban sites were computed. The absolute 8-hr maximum O3 concentrations were comparable in urban, rural and background sites. Strong relationships between the monthly 8-hr maximum O3 concentrations and categorical variables representing the fire frequency for each month in six buffer zones were computed. Fires incidents near the sites (less than 250 miles) in central Arizona, central Texas and western Mexico triggered a decrease of 8-hr maximum O3 concentration by 5 to 13 ppbv in urban and rural sites and an increase of 2 ppbv in Chiricahua due to the modifications of the VOC (volatile organic compounds)/NOx mixtures. Conversely, fire incidents in southeast US, Cuba and central Mexico contributed from 5 up to 19 ppbv due to mixing of aloft O3 formed during air transport. These findings indicated that regional fire incidents may trigger high O3 episodes, possible NAAQS violations and an increase of hospitalizations from asthma and COPD by 1-3% annually.

Historical Air Quality

The second part of the report looked at the historical levels of pollutants. The pollutants of most concern in the region are ozone (O3), carbon monoxide (CO) and particulate matter (PM10 and PM2.5.) PM10 is particulate matter that measures up to 10 micrometers in diameter; PM2.5 is particulate matter that measures less than 2.5 micrometers in diameter. Exceedances for ozone and particulate matter are routinely monitored in the Paso del Norte (PdN) airshed. An exceedance occurs when pollutant concentrations are higher than the level prescribed by the specific NAAQS. Not all exceedances are violations of the NAAQS and do not automatically make an area nonattainment. Violations of the NAAQS occur when the monitored levels of a pollutant exceed the form of the standard. Exceedances of the NAAQS for all three pollutants are routinely monitored in the Paso del Norte airshed. Exceedances of the PM10 NAAQS are monitored at all sites in the study region.

The study found that the spring months showed the most exceedances of PM10. Only 2 percent of days have 24-hour averages that exceed the NAAQS of 150 at monitoring sites in the Paso del Norte. Monitors located in the Paso del Norte air basin (Anthony, Chaparral, Desert View and Sunland Park City Yard) show slightly higher 24-hour PM10 averages than the monitors in Las Cruces and Deming. PM2.5 levels are highest during the winter and tend to drop off the rest of the year except for days with windblown dust. The number of monitored exceedances ranged from zero in 2009 to a high of 10 in 2011.

Palomas-Columbus Air Quality Study

The third section discussed the work that was done during the Palomas, Mexico-Columbus, New Mexico air quality study. This study was to investigate the impacts of the cattle feedlot on ambient air quality in Palomas, Mexico. It turned out after starting the study that the cattle were no longer being sent to the Palomas cattle facility, and we changed the scope of the project to accommodate the change in emission sources. We ended up changing the objectives to estimate the spatial and temporal distributions of PM10 concentrations, especially near fugitive dust sources, and to estimate fugitive dust contributions based on existing PM10 emissions information. During the study, three exceedances of the 24-hour PM10 National Ambient Air Quality Standards were observed in Palomas and two were observed in New Mexico. The two exceedances in New Mexico were during strong dust storms due to high winds. These episodes not only affected the Palomas/Columbus area but most of southern New Mexico and parts of the southern Great Plains as the dust plumes were transported by strong southwesterly winds. Several conclusions can be drawn from the PM10 samples in this study with respect to particle measurements, emission sources, and human exposure. The highest exposures to PM10 were from regional dust storms that brought in transported dust on top of wind-blown dust locally generated from erodible areas. Overall, the highest 24-hour averaged PM10 concentrations were measured at the CTSO site, south of the cattle facility. PM10 concentrations at that site over the study period averaged 78 µg/m3 with a median value of 75 µg/m3. The second highest average PM10 concentrations were measured at the CTSW site, west of the cattle facility. There the average daily PM10 was 74 µg/m3 and the median value was 69 µg/m3. An analysis of homogeneity across the study PM10 network showed that concentrations are highly variable on most days. There were three days when the PM10 concentrations varied by more than a factor of 10, and one day when the highest and lowest spanned more than 150 µg/m3.

Remote Sensing of Regional Dust Events

The fourth section reviewed our work done to use satellite remote sensing to estimate population exposure to extreme dust events in the region. As of the end of FY12, we have identified 442 days during the period from April 2000 to May 2012 when there were dust events. Using the tools and methods to extract plume outlines, we are in the process of building the geodatabase of dust plume outlines from imagery acquired during those 442 days. We are also investigating other data sources that may provide clues on the extent of dust plumes based on the NWS Cooperative observation network. Some of the observations go back to the 1890s and continue to the present. We also discussed some of the ongoing work in predicting dust episodes using the CHIMERE and DREAM model.

Microscopic Analysis of Aerosol Particles

The final section briefly reviewed some of the chemical analysis that is ongoing to understand the sources of particulate matter in the region. This section shows some of the recent results that we have received through the analysis of PM10 and PM2.5 filter samples from Sunland Park. We used a scanning electron microscope S-3400N Type II with Noran System Six 300 Nanotrace x-ray microanalysis system. This was done at the NMSU Microscopy Suite of the Core University Research Resources Laboratory. We began a microscopic analysis of a subset of the 47 mm PTFE Teflon filters of PM10 and PM2.5 aerosol collected at the Sunland Park City Yard site to observe individual particle morphologies and elemental composition. The vast majority of the particles in the 1 to 10 µm range are composed of geological materials such as silicon, calcium, iron and aluminum.