Maximum ozone concentrations in the southwestern US and Texas: Implications of growing predominance of background contribution

Archived Ozone Design Values (ODVs) provide smoothed temporal records of maximum ozone concentrations impacting monitoring sites throughout the US. Utilizing time series of ODVs recorded at sites along the US West Coast, we separately estimate ODV contributions from US background ozone and from production driven by US anthropogenic precursor emissions. Sondes launched from Trinidad Head in northern California measure the vertical distribution of baseline ozone transported ashore from the Pacific; this profile is reflected in the increase of the US background ODV contribution with monitoring site elevation in both rural and urban areas. The ODVs that would result from US background ozone alone are small at coastal, sea level locations (average ~45 ppb), but increase with altitude; above 1 km US background ODVs can exceed 60 ppb. US background ozone contributions now constitute the majority of the maximum ODVs throughout the US west coast region, including the Los Angeles urban area, which records the country’s highest ODVs. US anthropogenic emissions presently cause enhancements of 35 to 55 ppb to the maximum ODVs in the Los Angeles area; thus, local emission controls can further reduce ozone even though the background contribution is larger. In other US west coast urban areas ODV enhancements from US anthropogenic emissions are much smaller than the US background ODV contribution. The past decrease in US anthropogenic ODV enhancements from emission controls is larger than generally realized – a factor of more than 6 from 1980 to 2020, while US background ODV contributions varied to only a small extent over those four decades. Wildfire impacts on ODVs are significant in urban areas of the Pacific Northwest, but not over the vast northern US rural region. There is an indication that agricultural emissions of nitrogen oxides in California’s Salinas Valley increase downwind maximum ODVs by 5–10 ppb. Implications: In 2020 the ozone design values (ODVs) resulting from transported background ozone alone are now larger than the ODV enhancements from US anthropogenic precursor emissions, even in the Los Angeles urban area, where the nation’s highest ODVs are recorded. The US anthropogenic ODV enhancements have been reduced by more than a factor of 6 from 1980 to 2020. The maximum US background ODV contributions have varied somewhat, but in each of the US west coast urban areas it was 60 ppb or larger in 2000. These contributions are so large that reducing maximum urban ODVs to the 70 ppb required by the 2015 ozone NAAQS is very difficult. There remains relatively little room for further reducing ODVs through domestic emission controls alone. From this perspective, degraded US ozone air quality in the western US is primarily due to the US background ozone contribution, with the US anthropogenic enhancement making a significant, but smaller contribution. Notably, the US background ODV has slowly decreased (~1 ppb decade−1; Parrish, Derwent, and Faloona 2021) since the mid-2000s; cooperative, international emission control efforts aimed at continuing or even accelerating this background ozone decrease may be an effective approach to further ODV reductions, since the US background ODV is largely due to a hemisphere-wide, transported reservoir of ozone with contributions from all northern midlatitude continents. Given the major contribution of background ozone to observed ODVs, future reviews of the ozone NAAQS will be better informed if observational-based estimates of background ODV contributions are considered, in addition to model-derived estimates upon which past reviews have solely relied.

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.

Policy Relevant Background (PRB) ozone concentrations are defined by the United States (U.S.) Environmental Protection Agency (EPA) as those concentrations that would occur in the U.S. in the absence of anthropogenic emissions in continental North America (i.e., the U.S, Canada, and Mexico). Estimates of PRB ozone have had an important role historically in the EPA's human health and welfare risk analyses used in establishing National Ambient Air Quality Standards (NAAQS). The margin of safety for the protection of public health in the ozone rulemaking process has been established from human health risks calculated based on PRB ozone estimates. Sensitivity analyses conducted by the EPA have illustrated that changing estimates of PRB ozone concentrations have a progressively greater impact on estimates of mortality risk as more stringent standards are considered. As defined by the EPA, PRB ozone is a model construct, but it is informed by measurements at relatively remote monitoring sites (RRMS). This review examines the current understanding of PRB ozone, based on both model predictions and measurements at RRMS, and provides recommendations for improving the definition and determination of PRB ozone.

Satellite observations of in‐cloud ozone concentrations from the Ozone Monitoring Instrument and Microwave Limb Sounder instruments show substantial differences from background ozone concentrations. We develop a method for comparing a free‐running chemistry‐climate model (CCM) to in‐cloud and background ozone observations using a simple criterion based on cloud fraction to separate cloudy and clear‐sky days. We demonstrate that the CCM simulates key features of the in‐cloud versus background ozone differences and of the geographic distribution of in‐cloud ozone. Since the agreement is not dependent on matching the meteorological conditions of a specific day, this is a promising method for diagnosing how accurately CCMs represent the relationships between ozone and clouds, including the lower ozone concentrations shown by in‐cloud satellite observations. Since clouds are associated with convection as well as changes in chemistry, we diagnose the tendency of tropical ozone at 400 hPa due to chemistry, convection and turbulence, and large‐scale dynamics. While convection acts to reduce ozone concentrations at 400 hPa throughout much of the tropics, it has the opposite effect over highly polluted regions of South and East Asia.

The updated regulatory framework for demonstrating that future 8-hr ozone (O3) design values will be at or below the National Ambient Air Quality Standards (NAAQS) provides guidelines for the development of a State Implementation Plan (SIP) that includes methods based on photochemical modeling and analytical techniques. One of the suggested approaches is the relative reduction factor (RRF) for estimating the efficacy of emission reductions. In this study, the sensitivity of model-predicted responses towards emission reductions to the choice of meteorology and chemical mechanisms was examined. While the different modeling simulations generally were found to be in agreement on whether predicted future-year design values would be above or below the NAAQS for 8-hr O3 at a majority of the monitoring locations in the eastern United States, differences existed for a small percentage of monitors (~ 6.4%). Another issue investigated was the ability of the attainment demonstration procedure to predict changes in monitored O3 design values. A retrospective analysis was performed by comparing predicted O3 design values from model simulations using emission estimates for 1996 and 2001 with monitored O3 design values for 2001. Results indicated that an average gross error of ~5 ppb was present between modeled and observed design values and that, at ~27% of all sites, model-predicted and observed design values disagreed as to whether the design value was above or below the NAAQS. Retrospective analyses such as the one presented in this study can provide valuable insights into the strengths and limitations of modeling and analysis techniques used to predict future design values over time periods of a decade or more for the purpose of developing SIPs. Furthermore, such analyses could provide avenues for improvement and added confidence in the use of the RRF approach for addressing attainment of the NAAQS.

Ozone concentrations in air flowing into New York State

A modeling analysis of alternative primary and secondary US ozone standards in urban and rural areas

Prediction of maximum ozone concentration is of great importance, especially to alert the population and to allow the authorities to take preventive measures soon enough. Ozone concentration and meteoro‐logical variables are now observed each hour or every 10 min so that we nearly get continuous observations along time, i.e. functions, as covariates. Much work has been done in the statistical community to propose effective models for predicting ozone concentration one day ahead, but there has been much less effort to study methods that take the functional nature of these data into account. We propose here two non‐linear models based on kernel estimators that handle the functional characteristics of the data by means of a measure of proximity between observed functions. In addition, we use additive ideas to take exogeneous variables into account without being too sensitive to dimensionality effects.Such procedures are called multivariate functional non‐parametric approaches, since our models/estimates are non‐parametric (because of the non‐linear structure linking the explanatory and the response variables), functional (because the variables are curves) and multi‐dimensional (because we can have many functional explanatory variables).These models are used to forecast maximum ozone concentration in Toulouse (France). We compare them to more classical techniques and the results are promising. Copyright © 2004 John Wiley & Sons, Ltd.

Ozone generators of dielectric barrier discharge (DBD) are mainly used for water and waste water treatment. Recently, they are also used for cleaning of food product machines, semiconductors processes, pulp bleaching field and so on. It is well-known that ozone concentration composed by DBD type ozone generator decreases with time when high purity oxygen used for feed gas. This is named by us, ozone zero phenomenon (OZP). The causes of the phenomena have been investigated experimentally in the world wide industries us. One of the causes is considered as an electrode material by discharge in the generator metal oxides formed from stainless steel electrode. We have studied the ozone generation characteristics using high purity oxygen as a feed gas and ozone generator of which both electrodes covered with dielectrics. It was found that using only high purity oxygen as a feed gas, ozone concentration decreased from 200g/m3(N) to 54g/m3(N) during about 5 hours. However, adding 0.1vol% of nitrogen into oxygen, ozone concentration increased rapidly over the initial maximum ozone concentration of 216g/m3(N). After that, the concentration of ozone gradually decreased with time. Therefore, adding nitrogen into oxygen has the effect of recovery of ozone concentration in the same generator. The maximum ozone concentration was obtained when 0.1-0.6vol% of nitrogen gas was added to oxygen gas. OZP is caused by ozone generator even when both electrodes are covered with dielectrics. The metal oxide is produced on electrode is not the cause of OZP. Ozone concentration can be increased by adding nitrogen into oxygen.

Ozone in the urban atmosphere can accumulate from photochemistry involving nitrogen oxides, carbon monoxide, and volatile organic compounds mainly emitted from fossil fuel combustions and volatile chemical products. Concentrated ozone near the earth's surface has a detrimental impact on the ecosystem and our health. The Los Angeles Basin is a classic example of an urban region with long‐standing ozone pollution, frequently in violation of its standard, designated by the US Environmental Protection Agency (EPA). Studies have reported substantial declines of ozone and their precursor concentrations over the past half century in this area due to extensive pollution controls. Since 2000, however, the ozone design value has remained the same and has not been able to fully reach the air quality standard set by the EPA despite decreases in its precursor concentrations. To understand this phenomenon, we utilize a chemical transport modeling approach to reproduce historical ozone trends and to conduct sensitivity runs relative to a 2010 baseline. Based on our analysis of the model simulations comparing the weekends and weekdays, rather than focusing only on the weekly averages, we diagnose that the Los Angeles Basin is actually going under a significant transition in photochemistry toward a lower ozone concentration. This reveals how air quality management strategies are slowly moving towards a pathway of reducing ozone concentrations in the future. Our study, however, suggests that further reductions of NOx emissions can lead to continued improvement of ozone pollution in this area.

Characterizing the distinct modulation of future emissions on summer ozone concentrations between urban and rural areas over China

PurposeThis study aims to investigate, for the first time in the literature, the stochastic properties of the US aggregate health-care price inflation rate series, using the data on health-care inflation rates for a panel of 17 major US urban areas for the period 1966-2006.Design/methodology/approachThis goal is undertaken by applying the first- and second-generation panel unit root tests and the panel stationary test developed recently by Carrion-i-Silvestre et al. (2005) that allows for endogenously determined multiple structural breaks and is flexible enough to control for the presence of cross-sectional dependence.FindingsThe empirical findings indicate that after controlling for the presence of cross-sectional dependence, finite sample bias, and asymptotic normality, the US aggregate health-care price inflation rate series can be characterized as a non-stationary process and not as a regime-wise stationary innovation process.Research limitations/implicationsThe research findings apply to understanding of health-care sector price escalation in US urban areas. These findings have timely implications for the understanding of the data structure and, therefore, constructs of economic models of urban health-care price inflation rates. The results confirming the presence of a unit root indicating a high degree of inflationary persistence in the health sector suggests need for further studies on health-care inflation rate persistence using the alternative measures of persistence. This study’s conclusions do not apply to non-urban areas.Practical implicationsThe mean and variance of US urban health-care inflation rate are not constant. Therefore, insurers and policy rate setters need good understanding of the interplay of the various factors driving the explosive health-care insurance rates over the large US metropolitan landscape. The study findings have implications for health-care insurance premium rate setting, health-care inflation econometric modeling and forecasting.Social implicationsPayers (private and public employers) of health-care insurance rates in US urban areas should evaluate the value of benefits received in relation to the skyrocketing rise of health-care insurance premiums.Originality/valueThis is the first empirical research focusing on the shape of urban health-care inflation rates in the USA.

Long range transport of ozone and its precursors can significantly impact the air quality in downwind regions. The problem of regional transport of ozone has been studied for more than three decades in Europe and U.S but not yet in Southeast Asia. This study investigated the regional scale distribution of tropospheric ozone over the Continental South East Asia Region (CSEA) of Thailand, Burma, Cambodia, Lao and Vietnam. The Models-3 Community Multi-scale Air Quality (CMAQ modeling system, driven by the NCAR/Penn State Fifth-Generation Mesoscale Model (MM5), is used for the purpose. The model domain covers the longitude range from 91'E to 111°E and the latitude range from 5°N to 25°N. Two most recent ozone episodes of March 24-26, 2004 and January 2-4, 2005 were selected which represent the typical meteorological conditions for high ozone concentrations periods of a year. The episode analysis was made based on available data from 10 and 4 monitoring stations located in Bangkok of Thailand and Ho Chi Minh City (HCMC) of Vietnam, respectively. The episodes were characterized with hourly ozone levels above the National Ambient Air Quality Standards of Thailand and Vietnam of 100 ppb at a number of the monitoring stations. The maximum ground level concentrations of ozone for March 2004 and January 2005 episodes reached 173 ppb and 157 ppb, respectively, in the urban plume of the Bangkok Metropolitan Region (BMR). The simulations were performed with 0.5o 0.5° emission input data which was prepared from the regional anthropogenic emission inventory used in the Transport and Chemical Evolution over the Pacific (TRACE-P), and the biogenic emissions obtained from the Global Emissions Inventory Activity (GEIA). The simulated overall picture of ground level ozone concentrations over CSEA domain shows that the concentrations were high at the downwind areas at a considerable distance from large urban areas such as BMR and HCMC. During March 2004 episode the ozone plume moved northeastward following the Southwesterly monsoon and the maximum width of the modeled plume with the ozone above 100 ppb was about 70 km from BMR. For HCMC the ozone plume moved northward and the concentration in the city plume was lower with the width of isopleth of 50ppb of around 40 km. During the Jan 2005 episode the ozone plume moved southwestward following the Northeasterly monsoon and the width of the modeled plume with the ozone concentration above 100 ppb in BMR was 50 km while for HCMC the width of the 40ppb isopleth was about 30 km. The model performance was evaluated on the available observed hourly ozone concentrations. The model system was shown to be able to reproduce the peak ozone levels that occurred during the episodes at these two large urban areas, and capture the day by day variations during the selected episodes. The performance statistics MNBE, NGE, and UPA for the simulated ozone concentrations are within U.S. EPA guidance criteria and are comparable to those reported previous for other regional ozone simulations. It is shown that the MM5/CMAQ system is the suitable modeling tools for ozone prediction over the CSEA.

Ambient ozone measurements were conducted from the beginning of May 2003 to the end of October 2004 in the forest ecosystems of west Mediterranean mountains of Turkey. The ozone concentrations were estimated using a passive sampling method from the bottom of the valley (altitude 10 m) to the top of the mountain (1950 m), over 20 sites distributed all over the study area. Active continuous measurements of ozone were done at one of the monitoring site which helped to calibrate the concentrations of ozone obtained by passive method. The results indicated that ozone concentrations were in the range of 19–410 μg m−3. The yearly average of ozone was 89.37 ± 71.25 μg m−3. Generally, maximum ozone concentrations were measured at high altitude stations (1950 amsl) during spring and summer seasons, and minimum concentrations were measured at the locations near to the road traffic. The symptoms of probable ozone injury in the vicinity of passive ozone samplers were examined by collecting needle and leaf samples from the main native plants. According to the visual inspection of leaves and measurement of photosynthetic pigments of control plants and symptomatic leaves, out of 41 species of native plants, 11 species were identified as potential bioindicators of ozone. Ozone concentrations in the west Mediterranean part of Turkey appear to be high enough and of sufficient duration to cause foliar injury in a wide variety of native plants.

The air quality impacts of replacing 20% of the gasoline powered light duty vehicle milestraveled with plug-in hybrid electric vehicles (PHEVs) in the region served by thePennsylvania, New Jersey, Maryland classic grid are examined. Unutilized, base-loadnighttime electricity generating capacity is assumed to charge PHEVs that wouldsubsequently be used during urban commutes. The net impact of this scenario on theemissions of precursors to the formation of ozone is an increase in nitrogen oxide (NOx),volatile organic compound (VOC) and CO emissions from electricity generating unitsduring nighttime hours, and a greater decrease in NOx, VOC and CO from mobileemissions in urban areas during daytime hours. The changes in maximum daily 8 h ozoneconcentrations, predicted using a regional photochemical model (CAMx), are decreases inozone concentrations between 2 and 6 ppb that are widespread across the urban areas, andincreases in ozone concentrations of up to 8 ppb in highly localized areas. Air qualityindicators beyond maximum daily ozone concentration are also evaluated, and ingeneral indicate air quality improvements associated with the use of PHEVs.However, a limited number of air quality indicators worsened with the use ofPHEVs, suggesting that overall impacts of the use of PHEVs will be complex.