Nonattainment Areas Research Articles

UNDERSTANDING INTRA-NEIGHBORHOOD PATTERNS IN FINE PARTICULATE AIR POLLUTION USING MOBILE MONITORING IN BRADDOCK, PA

Background and Aims: Braddock, Pennsylvania, in the eastern suburbs of Pittsburgh, lies in a valley adjacent to the Monongahela River. An economically distressed area, Braddock is home to the Edgar Thomson Steel Works, one of the few remaining active steel mills in Pittsburgh. Braddock exceeds both the average annual (>15 µg/m3) and daily (>35 µg/m3) National Ambient Air Quality Standards (NAAQS) for particulate matter (PM2.5), and is situated in a federal PM2.5 non-attainment area. Methods: A mobile monitoring design was used to explore the within-neighborhood spatial and temporal (within-day and between-day) variability in PM2.5 and PM10. Our sampling route consisting of 25 designated stops, of 3- to 5-minute intervals, sampled in summer and winter months, during morning and afternoon hours, in 2010-2011. Ambient weather data was obtained from Pittsburgh International Airport, and examined to identify inversion events. Results: The PM2.5 and PM10 mobile monitoring data display some spatial variation between stops, and substantial temporal variations across days. Concentrations also differed substantiailly between morning and afternoon runs. The PM2.5/ PM10 ratio was generally high (0.8 to 1), suggesting a predominance of fresh combustion particles in our sampling area. For morning sampling runs, mean PM2.5 concentrations ranged from 31 to 55 µg/m3 (SD = 1.53 and 4.92 µg/m3, respectively), and mean PM10 concentrations ranged from 30 to 70 µg/m3 (SD = 1.64 and 7.68 µg/m3, respectively). During summer months, afternoon concentrations were significantly lower than in the morning for both PM2.5 and PM10, owing to morning inversions in the river valley. During the winter, concentrations were generally lower than during summer, but showed lesser diurnal variability, with no inversion events. Conclusions: These pilot data reveal significant diurnal and spatial variability in both PM2.5 and PM10 concentrations within Braddock. Results will inform the design of a stationary monitoring network, to be implemented and maintained as part of a longitudinal study on childhood asthma exacerbation in Braddock.

The tree BVOC index

Urban trees can produce a number of benefits, among them improved air quality. Biogenic volatile organic compounds (BVOCs) emitted by some species are ozone precursors. Modifying future tree planting to favor lower-emitting species can reduce these emissions and aid air management districts in meeting federally mandated emissions reductions for these compounds. Changes in BVOC emissions are calculated as the result of transitioning to a lower-emitting species mix in future planting. A simplified method for calculating the emissions reduction and a Tree BVOC index based on the calculated reduction is described. An example illustrates the use of the index as a tool for implementation and monitoring of a tree program designed to reduce BVOC emissions as a control measure being developed as part of the State Implementation Plan (SIP) for the Sacramento Federal Nonattainment Area.

The higher price of cleaner fuels: Market power in the rail transport of fuel ethanol

This paper provides evidence of market power in the transportation of ethanol used in reformulated gasoline and alternative transportation fuels. I estimate a reduced form model for railroad route-level prices. My identification strategy instruments for railroad entry, controls for selection and explicitly models capacity constraints. A detailed understanding of this industry is important because U.S. environmental policies seek to substantially expand ethanol use. Evidence of market power may alter the types of policies pursued by lawmakers. I find that ethanol shipment prices are lower for more competitive routes. I also find evidence that railroads price discriminate based on environmental regulation at route destinations. Monopolist prices for shipments to carbon monoxide non-attainment areas are 3% higher than shipments to other destinations. This price premium falls sharply with increased competition. This suggests a perverse result where environmental regulation increases the price of a clean input.

Low-Wind/High Particulate Matter Episodes in the Calexico/Mexicali Region

The U.S. Environmental Protection Agency (EPA) currently classifies Imperial County, CA, as a nonattainment area for PM10 (particulate matter [PM] ≤ 10 μm in diameter), and this region suffers from high rates of chronic bronchitis and childhood asthma. Although high annual and daily average PM levels can have negative health and economic effects, recent studies have identified an association between adverse health effects and short-term PM spikes of tens of micrograms per cubic meter. This study identified PM episodes in Calexico/Mexicali that involve PM concentration spikes with concentrations up to 10 times greater than those reported to cause adverse health effects. These episodes appear to be relatively common during the winter months, are associated with wind speeds below 2 m/sec and stable boundary level heights below 500 m, and can comprise a large portion of the 24-hr PM levels. The organic composition of the PM10 samples collected during the low-wind/high-PM episodes differed from that collected at other times. However, a preliminary source attribution identified only one significant difference between the source classes: agricultural burning accounted for 6.7% of organic-fraction PM10 for low-wind/high-PM episodes versus 0.25% at other times. This preliminary source attribution also revealed that motor vehicles were the most important relative contributor to organic PM10.

The Higher Price of Cleaner Fuels: Market Power in the Rail Transport of Fuel Ethanol

This paper provides evidence of market power in the transportation of ethanol used in reformulated gasoline and alternative transportation fuels. I estimate a reduced form model for railroad route-level prices. My identification strategy instruments for railroad entry, controls for selection and explicitly models capacity constraints. A detailed understanding of this industry is important because U.S. environmental policies seek to substantially expand ethanol use. Evidence of market power may alter the types of policies pursued by lawmakers. I find that ethanol shipment prices are lower for more competitive routes. I also find evidence that railroads price discriminate based on environmental regulation at route destinations. Monopolist prices for shipments to carbon monoxide non-attainment areas are 3% higher than shipments to other destinations. This price premium falls sharply with increased competition. This suggests a perverse result where environmental regulation increases the price of a clean input.

Geologic and infrastructure factors for delineating areas for clean coal: examples in Texas, USA

Texas has a wide variety of areas that can be targeted for new clean-coal facilities. These areas are delineated by mapping spatial linkages between coal- and lignite-bearing formations, groundwater and surface-water resources, and CO2 sinks in brine formations for long-term CO2 storage or in mature oil fields with potential for enhanced oil recovery (EOR). However, a variety of infrastructure factors make it feasible to also target numerous areas outside coal and lignite basins in Texas. These infrastructure factors include pipelines for delivery of CO2 to subsurface sinks and delivery of coal-produced hydrogen to refineries, ease of connection to existing transmission lines, distribution of nonattainment areas where new clean-coal facilities could be constructed and be compliant with strict air-quality standards, and railroads that can transport coal and other feedstock to new clean-coal facilities. Primary regions in Texas where favorably co-located CO2 source-sink factors related to coal and lignite trends include the Gulf Coast, the Eastern Shelf of the Permian Basin, and the Fort Worth Basin. However, areas outside coal and lignite basins, particularly the Permian Basin where a new clean-coal facility is being planned, also have clean-coal potential because of existing CO2 pipelines and proximity to EOR fields that can economically sustain new clean-coal facilities.

Assessment of air quality benefits from national air pollution control policies in China. Part II: Evaluation of air quality predictions and air quality benefits assessment

Following the meteorological evaluation in Part I, this Part II paper presents the statistical evaluation of air quality predictions by the U.S. Environmental Protection Agency (U.S. EPA)’s Community Multi-Scale Air Quality (Models-3/CMAQ) model for the four simulated months in the base year 2005. The surface predictions were evaluated using the Air Pollution Index (API) data published by the China Ministry of Environmental Protection (MEP) for 31 capital cities and daily fine particulate matter (PM 2.5, particles with aerodiameter less than or equal to 2.5 μm) observations of an individual site in Tsinghua University (THU). To overcome the shortage in surface observations, satellite data are used to assess the column predictions including tropospheric nitrogen dioxide (NO 2) column abundance and aerosol optical depth (AOD). The result shows that CMAQ gives reasonably good predictions for the air quality. The air quality improvement that would result from the targeted sulfur dioxide (SO 2) and nitrogen oxides (NO x) emission controls in China were assessed for the objective year 2010. The results show that the emission controls can lead to significant air quality benefits. SO 2 concentrations in highly polluted areas of East China in 2010 are estimated to be decreased by 30–60% compared to the levels in the 2010 Business-As-Usual (BAU) case. The annual PM 2.5 can also decline by 3–15 μg m −3 (4–25%) due to the lower SO 2 and sulfate concentrations. If similar controls are implemented for NO x emissions, NO x concentrations are estimated to decrease by 30–60% as compared with the 2010 BAU scenario. The annual mean PM 2.5 concentrations will also decline by 2–14 μg m −3 (3–12%). In addition, the number of ozone (O 3) non-attainment areas in the northern China is projected to be much lower, with the maximum 1-h average O 3 concentrations in the summer reduced by 8–30 ppb.

The Environmental Cost of Reducing Agricultural Fine Particulate Matter Emissions

The U.S. Environmental Protection Agency (EPA) revised the National Ambient Air Quality Standards (NAAQS) in 2006, reducing acceptable fine particulate matter (PM2.5) levels; state environmental protection agencies in states with nonattainment areas are required to draft State Implementation Plans (SIPs) detailing measures to reduce regional PM2.5 levels by reducing PM2.5 and PM2.5 precursor emissions. These plans need to account for increases in emissions caused by operating control technologies. Potential PM2.5 emissions reductions realized by adding a second set of dust cyclones were estimated for the cotton ginning industry. Increases in energy consumption were calculated based on dust cyclone air pressure drop. Additional energy required was translated into increased emissions using published emission factors and state emissions inventories. Reductions in gin emissions were compared with increases in emissions at the power plant. Because of the electrical energy required, reducing one unit of agricultural PM2.5 emissions at a cotton gin results in emitting 0.11–2.67 units of direct PM2.5, 1.39–69.1 units of PM2.5 precursors, 1.70–76.8 units of criteria pollutants, and 692–15,400 units of greenhouse gases at the point where electricity is produced. If regulations designed to reduce rural PM2.5 emissions increase electrical power consumption, the unintended net effect may be more emissions, increased environmental damage, and a greater risk to public health.

Formaldehyde and its relation to CO, PAN, and SO<sub>2</sub> in the Houston-Galveston airshed

Abstract. The Houston-Galveston Airshed (HGA) is one of the major metropolitan areas in the US that is classified as a nonattainment area of federal ozone standards. Formaldehyde (HCHO) is a key species in understanding ozone related air pollution; some of the highest HCHO concentrations in North America have been reported for the HGA. We report on HCHO measurements in the HGA from summer 2006. Among several sites, maximum HCHO mixing ratios were observed in the Houston Ship Channel (HSC), a region with a very high density of industrial/petrochemical operations. HCHO levels at the Moody Tower (MT) site close to downtown were dependent on the wind direction: southerly maritime winds brought in background levels (0.5–1 ppbv) while trajectories originating in the HSC resulted in high HCHO (up to 31.5 ppbv). Based on the best multiparametric linear regression model fit, the HCHO levels at the MT site can be accounted for as follows: 38.5±12.3% from primary vehicular emissions (using CO as an index of vehicular emission), 24.1±17.7% formed photochemically (using peroxyacetic nitric anhydride (PAN) as an index of photochemical activity) and 8.9±11.2% from industrial emissions (using SO2 as an index of industrial emissions). The balance 28.5±12.7% constituted the residual which cannot be easily ascribed to the above categories and/or which is transported into the HGA. The CO related HCHO fraction is dominant during the morning rush hour (06:00–09:00 h, all times are given in CDT); on a carbon basis, HCHO emissions are up to 0.7% of the CO emissions. The SO2 related HCHO fraction is significant between 09:00–12:00 h. After 12:00 h HCHO is largely formed through secondary processes. The HCHO/PAN ratios are dependent on the SO2 levels. The SO2 related HCHO fraction at the downtown site originates in the ship channel. Aside from traffic-related primary HCHO emissions, HCHO of industrial origin serves as an appreciable source for OH in the morning.

Improving ozone modeling in complex terrain at a fine grid resolution – Part II: Influence of schemes in MM5 on daily maximum 8-h ozone concentrations and RRFs (Relative Reduction Factors) for SIPs in the non-attainment areas

Part II presents a comprehensive evaluation of CMAQ for August of 2002 on twenty-one sensitivity simulations (detailed in Part I) in MM5 to investigate the model performance for O 3 SIPs (State Implementation Plans) in the complex terrain. CMAQ performance was quite consistent with the results of MM5, meaning that accurate meteorological fields predicted in MM5 as an input resulted in good model performance of CMAQ. In this study, PBL scheme plays a more important role than its land surface models (LSMs) for the model performance of CMAQ. Our results have shown that the outputs of CMAQ on eighteen sensitivity simulations using two different nudging coefficients for winds (2.5 and 4.5 × 10 −4 s −1, respectively) tend to under predict daily maximum 8-h ozone concentrations at valley areas except the TKE PBL sensitivity simulations (ETA M-Y PBL scheme with Noah LSMs and 5-layer soil model and Gayno-Seaman PBL) using 6.0 × 10 −4 s −1 with positive MB (Mean Bias). At mountain areas, none of the sensitivity simulations has presented over predictions for 8-h O 3, due to relatively poor meteorological model performance. When comparing 12-km and 4-km grid resolutions for the PX simulation in CMAQ statistics analysis, the CMAQ results at 12-km grid resolution consistently show under predictions of 8-h O 3 at both of valley and mountain areas and particularly, it shows relatively poor model performance with a 15.1% of NMB (Normalized Mean Bias). Based on our sensitivity simulations, the TKE PBL sensitivity simulations using a maximum value (6 × 10 −4) among other sensitivity simulations yielded better model performance of CMAQ at all areas in the complex terrain. As a result, the sensitivity of RRFs to the PBL scheme may be considerably significant with about 1–3 ppb in difference in determining whether the attainment test is passed or failed. Furthermore, we found that the result of CMAQ model performance depending on meteorological variations is affected on estimating RRFs for attainment demonstration, indicating that it is necessary to improve model performance. Overall, G_c (Gayo-Seaman PBL scheme) using the coefficient for winds, 6 × 10 −4 s −1, sensitivity simulation predicts daily maximum 8-h ozone concentration closer to observations during a typical summer period from May to September and provides generally low future design values (DVFs) at valley and mountain areas compared to other simulations.

POLICY:EPA’s Ground-Level Ozone Standard Redux

POLICY:EPA’s Ground-Level Ozone Standard Redux

Lead in Air: Adjusting to a New Standard

When it comes to industrial lead processing, The Doe Run Company’s smelter is in a class by itself. Perched on the banks of the Mississippi River in Herculaneum, Missouri, the smelter’s blast furnaces convert vast amounts of lower-grade ore into more than 125,000 tons of nearly pure commercial-grade lead every year. In operation since 1982, this is both the nation’s largest primary lead smelter and its largest point source for lead emissions, with just over 59 tons of lead released to the air in 2005, according to the most recent figures from the National Emissions Inventory of the U.S. Environmental Protection Agency (EPA). By comparison, that year’s next-highest emitter—a Missouri lead recycling facility also operated by Doe Run—released 12.4 tons. Doe Run’s smelter in Herculaneum may be the nation’s largest point source for air lead emissions, but it’s not the only one. The National Emissions Inventory, whose next release is expected 31 December 2010, lists 200 facilities emitting between one-half and 1 ton of the metal annually and 139 facilities emitting more than 1 ton. These facilities, which include smelters, battery recyclers, metal foundries, power plants, and airports, represent new and ongoing sources of lead air pollution that will soon draw additional scrutiny from the EPA. Among them, only one—Doe Run’s Herculaneum smelter—put its surrounding community out of compliance under the original National Ambient Air Quality Standard (NAAQS, usually pronounced “nax”) for lead under the Clean Air Act. That will soon change, however, for in 2008, the EPA dropped the lead NAAQS for the first time in 30 years, from 1.5 μg/m3 to 0.15 μg/m3. States have until 2017 to meet the new standard. But if 2005–2007 emissions data hold, up to 18 additional locations will be out of attainment with the new lead NAAQS, including communities in Alabama, Colorado, Florida, Illinois, Indiana, Minnesota, Missouri, New Jersey, Ohio, Pennsylvania, Tennessee, and Texas. Meanwhile, the emergence of new nonattainment areas puts a spotlight on point sources, or identifiable sources of concentrated emissions, which—in the EPA’s view—account for the dominant share of lead air risks in the United States today. “It’s appropriate to infer that point sources—especially now with the removal of lead from gas—are the main routes of exposure to lead in outdoor air, at least in this country,” says Lewis Weinstock, group leader of the EPA Ambient Air Monitoring Group. That view puts the EPA squarely at odds with the lead industry. David Weinberg, a lawyer with Battery Council International (BCI), a trade group in Washington, DC, argues that “legacy” contamination from old leaded gas and house paint contributes more to elevated blood lead than point-source emissions do. Exposure to legacy lead occurs both by ingesting contaminated soils and by inhaling resuspended road dusts and soils. “We’re making tremendous strides controlling industrial lead emissions with closed-loop cycles,” Weinberg says. “And as you lower ambient levels of concern, historic sources—i.e., residual paint and gas contamination—become increasingly important.” Philip J. Landrigan, a pediatrician and lead researcher at Mount Sinai School of Medicine, points out, however, that the dominant source of exposure for a particular child depends on where the child lives. “It is very important to document lead emissions from all of these sources,” he says, “because even the smallest exposures to lead are now understood to cause damage to the developing brains of young children.”

Validation of in-situ measurements of volatile organic compounds through flask sampling and gas chromatography/mass spectrometry analysis

Continuous monitoring of ambient non-methane hydrocarbons (NMHCs) by automated gas chromatographs equipped with flame ionization detection (termed in-situ GC/FID) with hourly data resolution was instated in ozone non-attainment areas throughout Taiwan. Performance of these on-site in-situ GCs was validated by manual flask sampling, as well as by in-lab gas chromatography/mass spectrometry (GC/MS) analysis. More than 50 VOCs from C 2 to C 11 were analyzed by both methods. Ninety flask samples were collected in series near an in-situ GC monitoring station in order to closely compare with the in-situ measurements. Both time-series and scatter plots from the two methods are displayed and discussed. It was found that over-simplified, un-humidified single-point calibration leading to surface loss was responsible for the bias in the in-situ method, resulting in greater error in accuracy as VOC volatility decreased. Although this over-estimate of the concentrations was found across all target VOCs, both methods were able to consistently capture the variability of ambient VOCs, with R 2 values greater than 0.9 for most of the major VOCs.

Biocrude oils from the fast pyrolysis of poultry litter and hardwood

The safe and economical disposal of poultry litter is becoming a major problem for the USA poultry industry. Current disposal methods such as land application and feeding to cattle are now under pressure because of pollution of water resources due to leaching, runoffs and concern for mad cow disease contamination of the food chain. Incineration or combustion is potentially applicable to large scale operations, but for small scale growers and EPA non-attainment areas, this is not a suitable option because of the high cost of operation. Thus, there is a need for developing appropriate technologies to dispose poultry litter. Poultry litters from broiler chicken and turkey houses, as well as bedding material were converted into biocrude oil in a fast pyrolysis fluidized bed reactor. The biocrude oil yields were relatively low ranging from 36 wt% to 50 wt% depending on the age and bedding material content of the litter. The bedding material (which was mostly hardwood shavings) biocrude oil yield was 63 wt%. The higher heating value (HHV) of the poultry litter biocrude oils ranged from 26 MJ/kg to 29 MJ/kg while that of the bedding material was 24 MJ/kg. The oils had relatively high nitrogen content ranging from 4 wt% to 8 wt%, very low sulfur (<1 wt%) content and high viscosity. The viscosities of the oils appeared to be a function of both the source of litter and the pyrolysis temperature. The biochar yield ranged from 27 wt% to 40 wt% depending on the source, age and composition of the poultry litter. The biochar ash content ranged from 24 wt% to 54 wt% and was very rich in inorganic components such as potassium and phosphorous.

Spot Fumigation: Fumigant Gas Dispersion and Emission Characteristics

Reducing emissions of volatile organic compounds (VOCs) from fumigant pesticides is mandatory in California, especially in "nonattainment areas" like the San Joaquin Valley that do not meet federal air quality standards. A two-year field study was conducted to examine the feasibility of site-specific fumigant application only at future tree sites with dramatically reduced amounts of fumigant chemicals on an orchard basis. Soil gas distribution and atmospheric emission of 1,3-dichloropropene and chloropicrin were measured after applying InLine using subsurface drip irrigation. It was predicted that except in the surface 20 cm of soil, satisfactory pest control could be achieved within a 15 cm radius from the injection point. Also, at radial distances of 15-51 cm from the point of fumigant injection, effective nematode control may be achieved. Cumulative atmospheric emission of the fumigants was estimated to be 18-23% of the applied active ingredients in plots that had been cover cropped with Sudan grass and 2-6% in plots that had remained bare for several months before treatment. Considering the significantly small amount of fumigant used on an orchard basis, the spot drip fumigation may achieve a 10-fold reduction in atmospheric VOCs load from fumigant pesticides.

What Do Emissions Markets Deliver and to Whom? Evidence from Southern California's NOx Trading Program

An advantage of cap-and-trade programs over more prescriptive environmental regulation is that compliance flexibility and cost effectiveness can make more stringent emissions reductions politically feasible. However, when markets (versus regulators) determine where emissions occur, it becomes more difficult to assure that mandated emissions reductions are equitably achieved. We investigate these issues in the context of Southern California's RECLAIM program by matching facilities in RECLAIM with similar California facilities also in nonattainment areas. Our results indicate that average emissions fell 20 percent at RECLAIM facilities relative to our counterfactual. Furthermore, observed changes in emissions do not vary significantly with neighborhood demographic characteristics. (JEL H23, L51, Q53, Q58)

Public Collaboration in Transportation

Rapid population growth, traffic congestion and air pollution from automobiles have made Environmental Protection Agency to designate Denton County as part of the Dallas - Fort Worth 8-hour non-attainment area. In 2001, county residents and elected officials petitioned the Texas Legislature to create the Denton County Transportation Authority (DCTA). In 2002, DCTA was created through a countywide election to provide environment friendly public transportation services. Soon DCTA embarked on a plan for collaboration with the public and various stakeholders. In this case study, efforts have been made to understand the reasons behind DCTA's plan for collaboration, the initiatives it undertook and the public's perception of such collaborative efforts. Based on evidences, it has been concluded that even a well designed plan of interaction can have structural flaws. Such flaws coupled with lack of understanding of local history can impede the establishment of a meaningful partnership with the local community.

Health risk estimation due to carbon monoxide pollution at different spatial levels in Santiago, Chile

The Metropolitan Region of Santiago has been declared as nonattainment area for carbon monoxide (CO). The data was based on seven air monitoring stations that do not necessarily represent the real population exposure. Usually, a series of coefficients that relates the concentration of pollutants with health effects (betas of the concentration-response equations) are used. For the calculation of these betas, normally, a city average air pollution concentration is used; nevertheless, these betas do not necessarily represent the real risk of exposure that the inhabitants are experimented. For this reason, this study estimates two aspects that are unknown and that are necessary to policymakers in public health decisions. First, estimate the exposure at a lower spatial resolution level and, second, estimate a concentration-response curve that differs spatially and depends on the proportion of susceptible groups. We followed the Air Pollution and Health, European Approach/Spanish Multicenter Study on the Relationship Between Air Pollution and the Mortality methodology for the determination of the short-term health effect due to CO population exposure at the three spatial levels (city, zone, and county). We found that there are different risks in cardiorespiratory mortality in the group over 64 years old associated to an unequal exposure to CO in Santiago city. The higher risks are in counties located to the south-east of the city. These finding confirm the necessity to face, in a different way, the approach when evaluating control strategies and policy decision to control air pollution in Santiago.

What Do Emissions Markets Deliver and to Whom? Evidence from Southern California's NOx Trading Program

A perceived advantage of cap-and-trade programs over more prescriptive environmental regulation is that enhanced compliance flexibility and cost effectiveness can make more stringent emissions reductions politically feasible. However, increased compliance flexibility can also result in an inequitable distribution of pollution. We investigate these issues in the context of Southern California's RECLAIM program. We match facilities in RECLAIM with similar California facilities also located in non-attainment areas. Our results indicate that emissions fell approximately 24 percent, on average, at RECLAIM facilities relative to our counterfactual. Furthermore, we find that observed changes in emissions do not vary significantly with neighborhood demographic characteristics.

Impacts of background ozone production on Houston and Dallas, Texas, air quality during the Second Texas Air Quality Study field mission

A major objective of the 2006 Second Texas Air Quality Study (TexAQS II) focused on understanding the effects of regional processes on Houston and Dallas ozone nonattainment areas. Here we quantify the contributions of background (continental scale) ozone production on Houston and Dallas air quality during TexAQS II using ensemble Lagrangian trajectories to identify remote source regions that impact Houston and Dallas background ozone distributions. Global‐scale chemical analyses, constrained with composition measurements from instruments on the NASA Aura satellite, are used to provide estimates of background composition along ensemble back trajectories. Lagrangian averaged O3 net photochemical production (production minus loss, P‐L) rates along the back trajectories are used as a metric to classify back trajectories. Results show that the majority (6 out of 9 or 66%) of the periods of high ozone in Houston were associated with periods of enhanced background ozone production. Slightly less than 50% (7 out of 15) of the days with high ozone in the Dallas Metropolitan Statistical Area (MSA) show enhanced background ozone production. Source apportionment studies show that 5‐day Lagrangian averaged O3 P‐L in excess of 15 ppbv/d can occur during continental‐scale transport to Houston owing to NOy enhancements from emissions within the Southern Great Lakes as well as recirculation of the Houston emissions. Dallas background O3 P‐L is associated with NOy enhancements from emissions within Chicago and Houston.