Ozone National Ambient Air Quality Research Articles

Photochemical model representation of ozone and precursors during the 2017 Lake Michigan ozone study (LMOS)

Several areas in the Lake Michigan region are violating the human health-based ozone (O3) National Ambient Air Quality Standard. Land-water meteorology driven build-up of precursor pollutants (NOX and VOC) from mobile and stationary sources undergo photochemical O3 production and result in seasonal high O3 episodes during the spring and summertime. Routine and specialized surface measurements coupled with airborne and remotely sensed measurements from the 2017 Lake Michigan Ozone Study (LMOS) provide an opportunity to evaluate photochemical grid model representation of these processes. The Community Multiscale Air Quality Model (CMAQ) was applied at a 4-km grid resolution for the Lake Michigan region and compared against routine and field study measurements to determine how well the modeling system captures emissions, meteorology, and chemical production during O3 episodes.The model captured day to day and diurnal variability in observed O3 along Lake Michigan but often missed peak O3. Surface level NO2 was generally well characterized, but the model seemed to be missing a significant source of VOC, likely both regional and local (not necessarily the same source sector) based on model sensitivities. On June 2, 2017, the model captured the timing of the lake to land breeze but underestimated near-surface wind speed which coincided with peak O3. The underestimation of surface O3 north of Chicago at Zion, Illinois, on this afternoon may be related to over-water vertical mixing, the modeled lake breeze being too weak to transport ozone and precursors back onshore, regional and aloft underprediction of O3, or some combination of each of these factors. Despite underpredictions of peak O3 at some monitors on certain days, the modeling system is useful for developing control scenarios for this region. Model-predicted O3 sensitivity to precursors matched other assessments and suggests both NOX and VOC anthropogenic emissions are important to reduce O3 in the Chicago area.

Weekend‐Weekday Implications and the Impact of Wildfire Smoke on Ozone and Its Precursors at Boulder Reservoir, Colorado Between 2017 and 2019

AbstractThe Northern Front Range of Colorado regularly exceeds the ozone (O3) National Ambient Air Quality Standard. This region is unique because it is impacted by emissions from urban activities (i.e., traffic and light industry) as well as from oil and natural gas production. Here, we summarize three years of observations from a new O3 monitoring site at the western edge of the region, located at the Boulder Reservoir. There were 41 days at the Boulder Reservoir in 2017, 2018, and 2019 when the maximum daily 8‐hour average O3 mixing ratio (MDA8 O3) exceeded 70 ppbv. Of these 41 high O3 days, 40 occurred between May and September, two were influenced by stratospheric intrusion events, one was influenced by a local industrial fire, and 13 of the days were impacted by wildfire smoke. Within the smoke‐free subset of data, weekend‐weekday differences in O3 versus nitrogen oxides (NOx) during 2018 and 2019 suggest NOx‐limited O3 production. Enhanced nonmethane volatile organic compounds (NMVOC) to NOx ratios are also observed on weekend days and are driven by weekend reductions in NOx. An analysis of 13 NMVOCs on days that had MDA8 O3 > 70 ppb showed that NMVOC abundances and their relative source contributions are variable at this location. Finally, we compare smoke‐impacted with smoke‐free conditions. At a given temperature, smoke‐impacted days have higher expected O3 mixing ratios than smoke free‐days. On average, benzene, toluene, and hexane are also elevated during smoke‐impacted periods.

Cumulative joint effects of air pollution and extreme heat events among hemodialysis patients

BACKGROUND AND AIM: Increasing number of studies have linked air pollution exposure with renal function decline and disease. However, there is a lack of data on its impact among end-stage renal disease (ESRD) patients and its potential modifying effect from extreme heat events (EHE). METHODS: Fresenius Kidney Care (FKC) records from 28 selected northeastern counties were used to pool daily all-cause mortality (ACM) and all-cause hospital admissions (ACHA) counts. County-level daily ambient PM2.5 and ozone were estimated using a high-resolution spatiotemporal coupled model and matched to ESRD patients based on ZIP codes of treatment sites. We used time-stratified case-crossover analyses to characterize acute exposures using same day (Lag 0) and cumulative exposure for up to 3 days (Lag 0-3). A distributed lag non-linear model (DLNM) framework was applied in non-stratified and EHE-stratified analyses. We used a nested model comparison hypothesis test to evaluate for interaction effects. RESULTS:From 2001 to 2016, the sample population consisted of 43,338 ESRD patients and yielded 5,217 deaths and 78,433 hospital admissions. A 10-unit increase in PM2.5 concentration was associated with a 5% increase in ACM (rate ratio [RRLag0-3], 1.05; 95% CI, 1.00-1.10) and same-day O3 (RRLag0, 1.02; 95% CI, 1.01-1.03) after adjusting for extreme heat exposures. Exceedance of ozone national ambient air quality standard (NAAQS) in the prior 3 days (Lag 0-3) was associated with a 29% increase in ACM (RRLag0-3, 1.29; 95% CI, 1.00-1.66) during EHE days. Data suggest that EHE can modify the association between ground-level Lag 0-3 ozone and mortality and Lag 0-3 PM2.5 exposures and mortality. CONCLUSIONS:Our findings suggest that extreme heat events may modify the association between air pollution and ACM among ESRD patients. National level assessments are needed to investigate how this relationship may vary by individual-level determinants and geographic region. KEYWORDS: Air pollution, Ozone, Particulate matter, Short-term exposure, Temperature extremes

Scientist Civic Engagement and the US Ozone Standards in 2020

BACKGROUND AND AIM: In 2020, the United States Environmental Protection Agency (EPA) proposed to retain, without revision, its national primary and secondary ozone National Ambient Air Quality Standards (NAAQS). As exposure scientists and environmental epidemiologists, we recognized that this decision may not have reflected the most updated research on ozone and population health effects. We thus aimed to inform the EPA of the state-of-the-science through official channels. METHODS: Within the North American Chapter (NAC) of the International Society for Environmental Epidemiology (ISEE), the Policy Committee worked as a team to gather, synthesize, and communicate evidence on ozone effects on population health. For the ozone NAAQS, one member attended the oral comment sessions and led the effort to draft and submit a written comment to the EPA. RESULTS:At the ISEE NAC Policy Committee, we recognized a proposed ruling that would have affected air quality in the US. We effectively organized to engage government stakeholders and communicate the latest research on ozone and population health. These actions entered into the public record a statement aimed at a general audience on the effects of ozone along with supporting scientific articles. Such materials could be considered in a court of law if and when a decision on the ozone NAAQS is contested. CONCLUSIONS:Environmental exposure and epidemiology research have the potential to inform policy decisions. The ISEE NAC Policy Committee provides an avenue for scientists to gain experience in communicating the research implications to decision-makers. KEYWORDS: Ozone, Research translation, Science communication, Policy

Urban core-downwind differences and relationships related to ozone production in a major urban area in Texas

San Antonio, the second-most populous city in Texas and the seventh-most populous city in the United States (US), has been designated a marginal non-attainment area by the US Environmental Protection Agency with respect to the 2015 ozone (O3) National Ambient Air Quality Standard. While stationary air quality monitoring sites are operated in the region by the Texas Commission on Environmental Quality (TCEQ), there are limited in situ field measurements for O3 and its precursors in the urban core. To better understand O3 dynamics in San Antonio, a suite of meteorological and gas instruments was deployed during May 2017. We incorporate field measurements from two campaign sites and one TCEQ stationary monitoring site into a zero-dimensional O3 model to characterize the local formation and destruction rates of O3, hydroxyl radical (OH) reactivity of volatile organic compounds (VOCs), O3 production efficiency, and O3 formation regime in the urban core and directly downwind of San Antonio. Upwind/downwind differences indicate the importance of photochemical processing of VOCs with carbon-carbon double bonds. San Antonio was mostly in a nitrogen oxide (NOX)-sensitive regime throughout the daytime during the campaign period, with O3 formation peaking at noon in the city center and early afternoon at the downwind region. Formaldehyde (HCHO), isoprene, and alkenes dominated VOC reactivity, with alkenes and isoprene from San Antonio's core (upwind) likely contributing to the downwind formation of HCHO and enhancing its OH reactivity. However, their direct impact on downwind O3 production was not observed. Model results suggest further strengthening NOX emission controls to decrease O3 formation in San Antonio.

Long-term Baseline Ozone Changes in the Western US: A Synthesis of Analyses

Quantification of the magnitude and long-term changes of ozone concentrations transported into the US is important for effective air quality policy development. We synthesize multiple published trend analyses of western US baseline ozone, and show that all results are consistent with an overall, non-linear change – a rapid increase (~5 ppb/decade) during the 1980s that slowed in the 1990s, maximized in the mid-2000s, and was followed by a slow decrease (~1 ppb/decade) thereafter. This non-linear change accounts for ~2/3 of the variance in 28 published linear trend analyses; we attribute the other 1/3 of the variance to unquantified autocorrelation in the analyzed data sets that result primarily from meteorologically-driven interannual ozone variability. Recent systematic changes in baseline ozone at the US West Coast have been relatively small - the standard deviation of the 2-year means over the 1990-2017 period is 1.5 ppb. International efforts to reduce anthropogenic precursor emissions from all northern mid-latitude sources could possibly reduce baseline ozone concentrations, thereby improving US ozone air quality. Implications Statement Ozone is an air pollutant with significant human and ecological health impacts. Air masses transported into the western US from over the Pacific Ocean carry ozone concentrations that are, on average, a large fraction of the US health standard. The US EPA policy assessment conducted for the recent review of the ozone National Ambient Air Quality Standard (NAAQS) found that 2016 regional average MDA8 ozone concentrations in the western US maximized in summer at ~52 ppb and that ~40 ppb of that maximum was contributed by ozone of natural and transported anthropogenic contributions. Thus, quantifying these trans-boundary background ozone concentrations has been identified as an important issue for a complete understanding of US air quality (e.g., see discussion in Introduction of Jaffe et al., 2018). Published analyses of temporal trends of these transported ozone concentrations vary widely, from early reports of increases to more recent reports of decreases. We show that the long-term ozone changes have been nonlinear, with substantial concentration increases (as large as ~5 ppb/decade) before the mid-2000s when a maximum was reached, followed by a small decrease of ~1 ppb/decade) thereafter. Superimposed on the overall changes is significant interannual variability that makes accurate determination of systematic trends over decade-scale time periods uncertain. The end of the previously increasing trends, and the recent decreases in transported ozone concentrations is good news for US air quality, as it eases the difficulty of achieving the ozone air quality standard.

The effect of an upwind non-attainment area on ozone in California's Sierra Nevada Mountains

Abstract The climate, topography, high population and associated emissions of California pose unique challenges in attaining the ozone (O3) National Ambient Air Quality Standard. California's Sierra Nevada Mountains are situated east, and downwind of, the San Joaquin Valley (SJV), which has some of the worst air quality in the US. This work reports surface and vertical O3 observations over the Sierra Nevada Mountains and the SJV from 1998 to 2018. Over this period, the O3 concentrations observed on highly polluted days (95th percentile) decreased, primarily because of summertime emission reductions. Analysis of surface site diurnal data highlights the impacts that the SJV has on the Sierra Nevada Mountains, particularly at lower elevations. O3 typically remains higher overnight at mountain sites, compared to SJV sites, and as a result mountain sites can have high cumulative exposure to O3. Evidence of local and transport effects on O3 trends across the Sierra Nevada Mountains is presented through examining of the timing of O3 exceedances and correlations with different surface sites and with O3 aloft. The data indicate a strong regional influence of emissions from the SJV over the Sierra Nevada Mountains and aloft up to 3 km.

Future-Year Ozone Isopleths for South Coast, San Joaquin Valley, and Maryland

Many areas of the United States are working toward achieving the 2015 ozone National Ambient Air Quality Standard (NAAQS) attainment level. The objective of this study was to develop future-year (2030) volatile organic compounds and nitrogen oxides (VOC-NOx) isopleth diagrams of the 4th highest maximum daily 8-h average ozone design value concentrations at monitors of interest in the South Coast Air Basin (SoCAB) and San Joaquin Valley (SJV) in California, and in Maryland. The simulation results showed there would be attainment of the 2015 ozone NAAQS in 2030 without further controls at the selected monitors: 27% in SoCAB, 57% in SJV, and 100% in Maryland. The SoCAB ozone isopleths developed in this study were compared with those reported in the South Coast Air Quality Management District 2016 Air Quality Management Plan. There are several differences between the two modeling studies, the results are qualitatively similar for most of the monitors in the relative amounts of additional emission reductions needed to achieve the ozone NAAQS. The results of this study provide insight into designing potential control strategies for ozone attainment in future years for areas currently in non-attainment. Additional photochemical modeling using these strategies can then provide confirmation of the effectiveness of the controls.

What Are the Net Benefits of Reducing the Ozone Standard to 65 ppb? An Alternative Analysis.

In October 2015, the United States Environmental Protection Agency (EPA) lowered the level of the ozone National Ambient Air Quality Standard (NAAQS) from 0.075 ppm to 0.070 ppm (annual 4th highest daily maximum 8-h concentration, averaged over three years). The EPA estimated a 2025 annual national non-California net benefit of $1.5 to $4.5 billion (2011$, 7% discount rate) for a 0.070 ppm standard, and a −$1.0 to $14 billion net benefit for an alternative 0.065 ppm standard. The purpose of this work is to present a combined toxicological and economic assessment of the EPA’s benefit-cost analysis of the 2015 ozone NAAQS. Assessing the quality of the epidemiology studies based on considerations of bias, confounding, chance, integration of evidence, and application of the studies for future population risk estimates, we derived several alternative benefits estimates. We also considered the strengths and weaknesses of the EPA’s cost estimates (e.g., marginal abatement costs), as well as estimates completed by other authors, and provided our own alternative cost estimate. Based on our alternative benefits and cost calculations, we estimated an alternative net benefit of between −$0.3 and $1.8 billion for a 0.070 ppm standard (2011 $, 7% discount rate) and between −$23 and −$17 billion for a 0.065 ppm standard. This work demonstrates that alternative reasonable assumptions can generate very difference cost and benefits estimates that may impact how policy makers view the outcomes of a major rule.

Comparing apples to oranges: Interpreting ozone concentrations from observational studies in the context of the United States ozone regulatory standard

In 2015, the United States Environmental Protection Agency (US EPA) set the ozone National Ambient Air Quality Standards (NAAQS) at 0.070 parts per million (ppm), for an annual 4th highest daily 8-hour (h) maximum average concentration, averaged over three years, with compliance based on the monitor with the highest concentrations. Numerous epidemiological studies have evaluated associations between ozone and health effects, but how the ozone concentrations derived from those studies can be compared to the ozone NAAQS is not clear, because of the complexity of the standard. The purpose of the present work was to determine how ozone summary metrics used in key epidemiology studies compare to the metrics that comprise the ozone regulatory value. Evaluation of epidemiology studies used for quantitative risk assessment in the 2015 ozone NAAQS review demonstrated that the most commonly used summary metrics that differed from the NAAQS were: 1-h maximum or 24-h average concentrations; multiple-day averages from 2 to 30 days; and averaging of ozone concentrations across all monitors in an area and over different months of the year. Using different ozone summary metrics to calculate the ozone regulatory value in twelve US cities for 2000–2002 or 2013–2015 generated alternative ozone regulatory values that were often substantively different and that may or may not vary commensurate with the regulatory standard. Comparison of epidemiology study metrics to other countries' ozone standards or guideline levels produces similar challenges as described here for the NAAQS. In conclusion, many of the ozone concentration metrics used in epidemiology studies cannot be directly compared to the ozone NAAQS, and using simple conversion ratios adds substantial uncertainty to concentration estimates. These summary metrics must be reconciled to the regulatory value before any judgements are made as to the protectiveness of current and alternative standards based on epidemiology study results.

Expected ozone benefits of reducing nitrogen oxide (NOx) emissions from coal-fired electricity generating units in the eastern United States

ABSTRACTOn hot summer days in the eastern United States, electricity demand rises, mainly because of increased use of air conditioning. Power plants must provide this additional energy, emitting additional pollutants when meteorological conditions are primed for poor air quality. To evaluate the impact of summertime NOx emissions from coal-fired electricity generating units (EGUs) on surface ozone formation, we performed a series of sensitivity modeling forecast scenarios utilizing EPA 2018 version 6.0 emissions (2011 base year) and CMAQ v5.0.2. Coal-fired EGU NOx emissions were adjusted to match the lowest NOx rates observed during the ozone seasons (April 1–October 31) of 2005–2012 (Scenario A), where ozone decreased by 3–4 ppb in affected areas. When compared to the highest emissions rates during the same time period (Scenario B), ozone increased ∼4–7 ppb. NOx emission rates adjusted to match the observed rates from 2011 (Scenario C) increased ozone by ∼4–5 ppb. Finally in Scenario D, the impact of additional NOx reductions was determined by assuming installation of selective catalytic reduction (SCR) controls on all units lacking postcombustion controls; this decreased ozone by an additional 2–4 ppb relative to Scenario A. Following the announcement of a stricter 8-hour ozone standard, this analysis outlines a strategy that would help bring coastal areas in the mid-Atlantic region closer to attainment, and would also provide profound benefits for upwind states where most of the regional EGU NOx originates, even if additional capital investments are not made (Scenario A).Implications: With the 8-hr maximum ozone National Ambient Air Quality Standard (NAAQS) decreasing from 75 to 70 ppb, modeling results indicate that use of postcombustion controls on coal-fired power plants in 2018 could help keep regions in attainment. By operating already existing nitrogen oxide (NOx) removal devices to their full potential, ozone could be significantly curtailed, achieving ozone reductions by up to 5 ppb in areas around the source of emission and immediately downwind. Ozone improvements are also significant (1–2 ppb) for areas affected by cross-state transport, especially Mid-Atlantic coast regions that had struggled to meet the 75 ppb standard.

Investigation of the influence of transport from oil and natural gas regions on elevated ozone levels in the northern Colorado front range

ABSTRACTThe Northern Colorado Front Range (NCFR) has been in exceedance of the ozone National Ambient Air Quality Standard (NAAQS) since 2004, which has led to much debate over the sources of ozone precursors to the region, as this area is home to both the Denver, CO, metropolitan area and the Denver–Julesburg Basin, which has experienced rapid growth of oil and natural gas (O&NG) operations and associated emissions. Several recent studies have reported elevated levels of atmospheric volatile organic compounds (VOCs) as a result of O&NG emissions and the potential for significant ozone production from these emissions, despite implementation of stricter O&NG VOC emissions regulations in 2008. Approximately 88% of 1-hr elevated ozone events (>75 ppbv) occur during June–August, indicating that elevated ozone levels are driven by regional photochemistry. Analyses of surface ozone and wind observations from two sites, namely, South Boulder and the Boulder Atmospheric Observatory, both near Boulder, CO, show a preponderance of elevated ozone events associated with east-to-west airflow from regions with O&NG operations in the N-ESE, and a relatively minor contribution of transport from the Denver Metropolitan area to the SE-S. Transport from upwind areas associated with abundant O&NG operations accounts for on the order of 65% (mean for both sites) of 1-hr averaged elevated ozone levels, while the Denver urban corridor accounts for 9%. These correlations contribute to mounting evidence that air transport from areas with O&NG operation has a significant impact on ozone and air quality in the NCFR.Implications: This article builds on several previous pieces of research that implied significant contributions from oil and natural gas emissions on ozone production in the Northern Colorado Front Range. By correlating increased ozone events with transport analyses we show that there is a high abundance of transport events with elevated ozone originating from the Denver–Julesburg oil and natural gas basin. These findings will help air quality regulators to better assess contributing sources to ozone production and in directing policies to curb ozone pollution in this region.

Projected ozone trends and changes in the ozone-precursor relationship in the South Coast Air Basin in response to varying reductions of precursor emissions

ABSTRACTThis study examined the effects of varying future reductions in emissions of oxides of nitrogen (NOx) and volatile organic compounds (VOC) on the location and magnitude of peak ozone levels within California’s South Coast Air Basin (SoCAB or Basin). As ozone formation is currently VOC-limited in the Basin, model simulations with 2030 baseline emissions (−61% for NOx and −32% for VOC from 2008) predict 10–20% higher peak ozone levels (i.e., NOx disbenefit) in the western and central SoCAB compared with the 2008 base simulation. With additional NOx reductions of 50% beyond the 2030 baseline emissions (−81% from 2008), the predicted ozone levels are reduced by about 15% in the eastern SoCAB but remain comparable to 2008 levels in the western and central Basin. The Basin maximum ozone site shifts westward to more populated areas of the Basin and will result potentially in greater population-weighted exposure to ozone with even a relatively small shortfall in the required NOx reductions unless accompanied by additional VOC reductions beyond 2030 baseline levels. Once committed to a NOx-focused control strategy, NOx reductions exceeding 90% from 2008 levels will be necessary to attain the ozone National Ambient Air Quality Standards (NAAQS). The findings from this study and other recent work that the current VOC emission estimates are underestimated by about 50% suggest that greater future VOC reductions will be necessary to reach the projected 2030 baseline emissions. Increasing the base year VOC emissions by a factor of 1.5 result in higher 2008 baseline ozone predictions, lower relative response factors, and about 20% lower projected design values. If correct, these findings have important implications for the total and optimum mix of VOC and NOx emission reductions that will be required to attain the ozone NAAQS in the SoCAB.Implications: Results of this study indicate that ozone levels in the western and central SoCAB would remain the same or increase with even a relatively small shortfall in the projected NOx reductions under planned NOx-focused controls. This possibility, therefore, warrants a rigorous analysis of the costs and effects of varying reductions of VOC and NOx on the formation and combined health impacts of ozone and secondary particles. Given the nonlinearity of ozone formation, such analyses should include the implications of gradually increasing global background ozone concentrations and the Basin’s topography and meteorology on the practical limits of alternative emission control strategies.

부산지역 고농도 오존일의 선행 기상 특성 연구

Comparing to the other air pollutants like <TEX>$SO_2$</TEX>, CO, the number of exceedance of the ozone national ambient air quality standard(NAAQS) and the ozone warning increased recently in Busan. The purpose of this study is to find out the preliminary symptoms for high ozone days in Busan area. In order to find out the preliminary symptoms, the hourly ozone data at air quality monitoring stations and the hourly meterological parameters at Busan regional meteorological 2007 to 2013 were used for the analysis. Averaged daily max ozone concentration was the highest(0.055 ppm) at Noksan and Youngsuri in the ozone season from 2007 to 2013. The horizontal distributions of daily max. ozone including all stations in Busan at high ozone days(the day exceeding 0.1 ppm of ozone concentration at least one station) were classified from two to five clusters by hierarchial cluster analysis. The meteorological variables showing strong correlation with daily max. ozone were the daily mean dew point temperature, averaged total insolation, the daily mean relative humidity and the daily mean cloud amount. And the most frequent levels were <TEX>$19-23^{\circ}C$</TEX> in dew point temperature, <TEX>$21-24 MJ/m^2$</TEX> in total insolation on the day before, <TEX>$2.6-3.0 MJ/m^2$</TEX> on the very day, 67-80% in relative humidity and 0-3 in cloud amount.

Are the elements of the proposed ozone National Ambient Air Quality Standards informed by the best available science?

The United States Environmental Protection Agency (US EPA) issues National Ambient Air Quality Standards (NAAQS) for six criteria pollutants, including ozone. Each standard has four elements: an indicator, level, averaging time, and form. Ozone levels (i.e., air concentrations) alone in scientific studies are not directly comparable to the “level” element of the NAAQS because the standard considers the level in the context of its relation to the remaining elements. Failure to appreciate this has led to misunderstandings regarding NAAQS that would be health-protective. This can be seen with controlled human ozone exposure studies, which often involved small numbers of people exercising quasi-continuously for a long duration at an intensity not common in the general population (and unlikely achievable by most sensitive individuals), under worst-case exposure profiles. In addition, epidemiology studies have used different averaging times and have had methodological limitations that may have biased results. Such considerations can make it difficult to compare ozone levels and results across studies and to appropriately apply them in a NAAQS evaluation. Relating patterns and circumstances of exposure, and exposure measurements, to all elements of the NAAQS can be challenging, but if US EPA fully undertook this, it would be evident that available evidence does not indicate that proposed lower ozone standards would be more health protective than the current one.

Evaluation of adverse human lung function effects in controlled ozone exposure studies

The US EPA is evaluating controlled human ozone exposure studies to determine the adequacy of the current ozone National Ambient Air Quality Standard of 75 ppb. These studies have shown that ozone exposures of 80 ppb and greater are associated with lung function decrements. Here, we critically review studies with exposures below 80 ppb to determine the lowest ozone concentration at which decrements are causally associated with ozone exposure and could be considered adverse using the Adverse Effects/Causation Framework. Regarding causation, the framework includes consideration of whether exposure-related effects are primary or secondary, statistically significant, isolated or independent, or due to study limitations. Regarding adversity, the framework indicates one should consider whether effects are adaptive, compensatory, precursors to an apical effect, severe, transient and/or reversible. We found that, at exposures below 72 ppb ozone, lung function effects are primary effects, but are isolated, independent and not statistically different compared to effects observed during filtered air exposure, indicating a lack of causation. Up to 72 ppb, lung function effects may be precursors to an apical effect, but are not likely adverse because they are transient, reversible, of low severity, do not interfere with normal activity and do not result in permanent respiratory injury or progressive respiratory dysfunction. Overall, these studies do not demonstrate a causal association between ozone concentrations in the range of the current National Ambient Air Quality Standard and adverse effects on lung function.

A Direct Sensitivity Approach to Predict Hourly Ozone Resulting from Compliance with the National Ambient Air Quality Standard

In setting primary ambient air quality standards, the EPA's responsibility under the law is to establish standards that protect public health. As part of the current review of the ozone National Ambient Air Quality Standard (NAAQS), the US EPA evaluated the health exposure and risks associated with ambient ozone pollution using a statistical approach to adjust recent air quality to simulate just meeting the current standard level, without specifying emission control strategies. One drawback of this purely statistical concentration rollback approach is that it does not take into account spatial and temporal heterogeneity of ozone response to emissions changes. The application of the higher-order decoupled direct method (HDDM) in the community multiscale air quality (CMAQ) model is discussed here to provide an example of a methodology that could incorporate this variability into the risk assessment analyses. Because this approach includes a full representation of the chemical production and physical transport of ozone in the atmosphere, it does not require assumed background concentrations, which have been applied to constrain estimates from past statistical techniques. The CMAQ-HDDM adjustment approach is extended to measured ozone concentrations by determining typical sensitivities at each monitor location and hour of the day based on a linear relationship between first-order sensitivities and hourly ozone values. This approach is demonstrated by modeling ozone responses for monitor locations in Detroit and Charlotte to domain-wide reductions in anthropogenic NOx and VOCs emissions. As seen in previous studies, ozone response calculated using HDDM compared well to brute-force emissions changes up to approximately a 50% reduction in emissions. A new stepwise approach is developed here to apply this method to emissions reductions beyond 50% allowing for the simulation of more stringent reductions in ozone concentrations. Compared to previous rollback methods, this application of modeled sensitivities to ambient ozone concentrations provides a more realistic spatial response of ozone concentrations at monitors inside and outside the urban core and at hours of both high and low ozone concentrations.

Air quality impacts of motor vehicle emissions in the south coast air basin: Current versus more stringent control scenario

States are working to comply with the ozone National Ambient Air Quality Standards (NAAQS). Often, regulations restricting vehicle emissions are promulgated in order to attain compliance with the NAAQS. Currently, more stringent vehicle emission regulations are being considered by government agencies. This paper compares emissions from passenger cars and light duty trucks under the current California Low Emission Vehicle (LEV II) standards to a control scenario which was anticipated in 2008 to become LEV III (referred to as “more stringent control” in this paper) and determines if the scenario would result in additional improvements to air quality in California’s South Coast Air Basin. The air quality modeling was performed using the Community Multi-scale Air Quality Model (CMAQ) for years 2005, 2014 and 2020. The more stringent control sensitivity study simulated a scenario in which all new passenger cars and light duty trucks in the California South Coast Air Basin in year 2016 achieve Super Ultra-Low Emission Vehicle (SULEV) tail pipe emissions, zero evaporative emissions and more stringent aggressive driving requirements. The total on-road vehicles emissions difference when averaged across the South Coast Air Basin showed the more stringent scenario compared to LEV II to have reductions of 1% for oxides of nitrogen (NOx), 1% for as reactive organic gases (ROG) and 5% for carbon monoxide (CO) in 2030. LEV II modeled ozone levels in the western areas of the basin increased in 2014 and 2020 as compared to 2005, because these areas are VOC-sensitive and the reductions in NOx emissions in these regions are larger than the VOC reductions. In other areas of the South Coast Basin, ozone is reduced by 1.5% or less. The more stringent control scenario modeled levels of ozone have a maximum decrease from LEV II levels by 1% or less in 2014 and 1.5% or less in 2020.

Rural Southeast Texas Air Quality Measurements during the 2006 Texas Air Quality Study

ABSTRACT The authors conducted air quality measurements of the criteria pollutants carbon monoxide, nitrogen oxides, and ozone together with meteorological measurements at a park site southeast of College Station, TX, during the 2006 Texas Air Quality Study II (TexAQS). Ozone, a primary focus of the measurements, was above 80 ppb during 3 days and above 75 ppb during additional 8 days in summer 2006, suggestive of possible violations of the ozone National Ambient Air Quality Standard (NAAQS) in this area. In concordance with other air quality measurements during the TexAQS II, elevated ozone mixing ratios coincided with northerly flows during days after cold front passages. Ozone background during these days was as high as 80 ppb, whereas southerly air flows generally provided for an ozone background lower than 40 ppb. Back trajectory analysis shows that local ozone mixing ratios can also be strongly affected by the Houston urban pollution plume, leading to late afternoon ozone increases of as high as 50 ppb above background under favorable transport conditions. The trajectory analysis also shows that ozone background increases steadily the longer a southern air mass resides over Texas after entering from the Gulf of Mexico. In light of these and other TexAQS findings, it appears that ozone air quality is affected throughout east Texas by both long-range and regional ozone transport, and that improvements therefore will require at least a regionally oriented instead of the current locally oriented ozone precursor reduction policies. IMPLICATIONS Ozone National Ambient Air Quality Standard (NAAQS) violations in the two major Texas metropolitan areas have been occurring for decades. Recent data show that high ozone concentrations in east Texas are not limited to the Houston and Dallas/Fort Worth areas, but can be transported far downwind, possibly leading to NAAQS violations in rural areas. This paper provides an assessment of rural ozone concentrations in Brazos County, 120 km northwest of Houston during summer 2006, showing that this area likely violated the NAAQS, in part due to long-range transport importing high ozone background concentrations, in part due to impacts of the Houston pollution plume under southeast wind directions.

Impact of Biogenic Emission Uncertainties on the Simulated Response of Ozone and Fine Particulate Matter to Anthropogenic Emission Reductions

ABSTRACT The role of emissions of volatile organic compounds and nitric oxide from biogenic sources is becoming increasingly important in regulatory air quality modeling as levels of anthropogenic emissions continue to decrease and stricter health-based air quality standards are being adopted. However, considerable uncertainties still exist in the current estimation methodologies for biogenic emissions. The impact of these uncertainties on ozone and fine particulate matter (PM2.5) levels for the eastern United States was studied, focusing on biogenic emissions estimates from two commonly used biogenic emission models, the Model of Emissions of Gases and Aerosols from Nature (MEGAN) and the Biogenic Emissions Inventory System (BEIS). Photochemical grid modeling simulations were performed for two scenarios: one reflecting present day conditions and the other reflecting a hypothetical future year with reductions in emissions of anthropogenic oxides of nitrogen (NOx). For ozone, the use of MEGAN emissions resulted in a higher ozone response to hypothetical anthropogenic NOx emission reductions compared with BEIS. Applying the current U.S. Environmental Protection Agency guidance on regulatory air quality modeling in conjunction with typical maximum ozone concentrations, the differences in estimated future year ozone design values (DVF) stemming from differences in biogenic emissions estimates were on the order of 4 parts per billion (ppb), corresponding to approximately 5% of the daily maximum 8-hr ozone National Ambient Air Quality Standard (NAAQS) of 75 ppb. For PM2.5, the differences were 0.1–0.25 μg/m3 in the summer total organic mass component of DVFs, corresponding to approximately 1–2% of the value of the annual PM2.5 NAAQS of 15 μg/m3. Spatial variations in the ozone and PM2.5 differences also reveal that the impacts of different biogenic emission estimates on ozone and PM2.5 levels are dependent on ambient levels of anthropogenic emissions. IMPLICATIONS The findings presented in this study demonstrate that uncertainties in biogenic emission estimates due to different emission models can have a significant effect on the model estimates of ozone and PM2.5 concentrations; specifically, the changes in these concentrations due to reductions in anthropogenic emissions considered in regulatory modeling scenarios. These results point to the need for further research aimed at improving biogenic emission estimates as well as better characterizing their dependency on environmental factors and the fate of these emissions once released into the atmosphere.