Ozone concentrations, ambient

R is hydrogen, alkenyl, or alkyne. In remote tropospheric air where NO concentrations ate sometimes quite low, HO2 radicals can react with ozone (HO2 + O3 — HO + 2 O2) and result in net ozone destmction rather than formation. The ambient ozone concentration depends on cloud cover, time of day and year, and geographical location. 

Although the naturally occurring concentration of ozone at the earth s surface is low, the distribution has been altered by the emission of pollutants, primarily by automobiles but also from industrial sources which lead to the formation of ozone. The strategy for controlling ambient ozone concentrations arising from automobile exhaust emissions is based on the control of hydrocarbons, CO, and NO via catalytic converters. As a result, peak ozone levels in Los Angeles, for instance, have decreased from 0.58 ppm in 1970 to 0.33 ppm in 1990, despite a 66% increase in the number of vehicles. 

Selective Catalytic Reduction of Nitrogen Oxides The traditional approach to reducing ambient ozone concentrations has been to reduce VOC emissions, an ozone precurssor. In many areas, it has now been recognized that ehmination of persistent exceedances of the National Ambient Air Qnality Standard for ozone may reqnire more attention to reductions in the other ingredients in ozone formation, nitrogen oxides (NOJ. In such areas, ozone concentrations are controlled by NO rather than VOC emissions. 

Yuska DE, Skelly JM, Ferdinand JA, Stevenson RE, Savage JE, Mulik JD, Etines A. 2003. Use of bioindicators and passive sampling devices to evaluate ambient ozone concentrations in north central Pennsylvania. Environ Pollut 125 71-80. 

Differences in measurement methods include analyzer systems based both on the same and on different measurement principles. The average standard deviation in the performance of different chemiluminescent ozone instruments that are sampling the same ambient air both with and without an added ozone concentration of 0.(X)2-0.5 ppm is 6-10%. Field studies comparing an ultraviolet monitor with several chemiluminescent monitors showed correlation coefficients for hourly averages of 0.80-0.95 between various pairs of instruments. Hourly averages for about 500 pairs of values at ambient ozone concentrations of 0.005-0.100 ppm showed deviations of 3-23% between the average values for paired instruments. 

Altshuler, S. L., T. D. Arcado, and D. R. Lawson, Weekday vs. Weekend Ambient Ozone Concentrations Discussion and Hypotheses with Focus on Northern California, J. Air Waste Manage. Assoc., 45, 967-972 (1995). 

The reaction between olefins and ozone produces light that can be measured and related to the concentration of the reactants. One of the preferred methods for measuring ambient ozone concentrations utilizes the chemiluminescence generated in the ozone-ethylene reaction for detection. Recently, Hills and Zimmerman (16) described the use of this detection principle for determining hydrocarbon concentrations. They utilized the chemiluminescence created when ozone reacts with isoprene for development of a continuous, fast-response isoprene analyzer. This real-time isoprene system is reported to be linear over three orders of magnitude and to have a detection limit of about 1 ppbv. Because the system doesn t include a preseparation of hydrocarbons, interferences from other olefins (ethylene, propylene, and so forth) could occur. Thus far the chemiluminescent detector has been used to monitor isoprene emissions under conditions in which the concentrations of olefins that could interfere are negligible compared to those of the biogenic hydrocarbon. 

An important field study conducted at various sites throughout the United States involved the exposure of crop plants to either ambient air at each site, or to a typical background ozone concentration of 25 ppb. Symptoms of acute ozone injuries were observed at all five of the study sites, although the damages were more frequent and severe in the southwest. On average, it was estimated that exposures to ambient ozone concentrations caused yield decreases of about 53-56% in lettuce, 14-17% in peanut, 10% in soybean, and 7% in turnip. Overall, it has been estimated that ozone causes crop losses equivalent to 2-4% of the potential yield in the United States, resulting in 3 billion in agricultural losses each year. 

NO, Substitution. As provided in the CAA [section 182(c)(2)(C)], NO, control may be substituted for the VOC control required to meet the post-1996 VOC emissions reductions progress requirements or may be combined with VOC control in order to maximize the reduction in ozone air pollution for purposes of meeting those requirements. In order to substitute NO reductions for VOC, the State must demonstrate to EPA, consistent with EPA guidance, that the NO, reductions would result in reductions in ambient ozone concentrations at least equivalent to that which would result from the amount of VOC emission reductions otherwise required. 

Natural ambient ground level concentrations of ozone, not influenced by ozone generated from NO / are normally around 40-80 g/m summer daily average. However, concern over the level of ozone concentrations in Europe has grown since the hot dry summer of 1976 when elevated concentrations of ozone were found. In Table 4.5(a) overleaf we show measured ambient ozone concentrations in five countries in the EEC and in Norway. 

On the other hand, ozone was S3mthesized in laboratories during this time, and an Irish chemist. Hartley, came up with a method for measuring absorption spectmm. As a result, it was found that ozone absorbs ultraviolet light most strongly at 200-320 nm, and this absorption band was therefore named the Hartley band after the chemist. Today, a standard method to measure ambient ozone concentration is to use an UV absorption instrument, which is based on the Hartley band. Data on the absorption spectrum of ozone took on even greater significance for chemistry of the atmosphere when it led to the discovery of the ozone layer in the stratosphere. Prior to this, scientists had measured the solar spectrum and learned that ultraviolet... 

Environmental Impact of Ambient Ozone. Ozone can be toxic to plants, animals, and fish. The lethal dose, LD q, for albino mice is 3.8 ppmv for a 4-h exposure (156) the 96-h LC q for striped bass, channel catfish, and rainbow trout is 80, 30, and 9.3 ppb, respectively. Small, natural, and anthropogenic atmospheric ozone concentrations can increase the weathering and aging of materials such as plastics, paint, textiles, and mbber. For example, mbber is degraded by reaction of ozone with carbon—carbon double bonds of the mbber polymer, requiring the addition of aromatic amines as ozone scavengers (see Antioxidants Antiozonants). An ozone decomposing polymer (noXon) has been developed that destroys ozone in air or water (157). 

The NAAQS are the allowable ambient (outdoor) concentrations that must be maintained in order to protect public health and welfare. Limits have been set for carbon monoxide (CO), lead (Pb), nHrogen dioxide (NOJ, ozone (Oj), sulfur dioxide (SOJ, and particulate matter (PM j. EPA is currently reviewing the adequacy of the ozone and PM,g standards. 

A critical question concerning atmospheric concentrations of ozone and other photochemical oxidants is What fraction of the observed values in each locale can be controlled by reduction of emissions Some contend that natural background concentrations exceed the federal ambient air quality standard (0.08 ppm). Another point of view is that background ozone concentrations rarely exceed about 0.05-0.06 ppm at the surface and that higher concentrations are caused by man-made sources. 

Descriptions of field studies of power-plant stack plumes were given by Davis et al. The ozone concentration appears to be lower in regions of high sulfur dioxide content. At 32 km downwind from the stacks, it was claimed that the ozone concentration in the plume (now 11 km wide) is higher than the ambient concentration ( 0.08 ppm) by approximately 0.02 ppm. Simultaneous measurements of nitric oxide and nitrogen dioxide were integrated across the plume. Values of the ratio of nitric... 

Nonurban oxidant measurements in Ohio were reported by Neligan and Angus. Concentrations of 0.18 and 0.12 ppm were reported for rural sites in Wilmington and McConnelsville, respectively. At the same time, urban sites had similar concentrations. However, the nonurban sites violated the ambient air quality standard more frequently than the urban sites. Trajectory analysis showed that ozone concentrations of 0.04-0.06 ppm were found in air masses that had not passed over anthropogenic hydrocarbon sources. These may have been examples of naturally occurring oxidant. Airborne hydrocarbon bag samples were obtained over 6-min... 

A dramatic departure of ozone measurements from total oxidant measurements has b Mi reported for the Houston, Texas, area. Side-by-side measurements suggested that either method was a poor predictor of the other. Consideration was given to known interferences due to oxides of nitrogen, sulfur dioxide, or hydrogen sulfide, and the deviations still could not be accounted for. In the worst case, the ozone measurements exceeded the national ambient air quality standard for 3 h, and the potassium iodide instrument read less than 15 ppb for the 24-h period. Sulfur dioxide was measured at 0.01-0.04 ppm throughout the day. Even for a 1 1 molar influence of sulfur dioxide, this could not explain the low oxidant values. Regression analysis was carried out to support the conclusion that the ozone concentration is often much higher than the nonozone oxidant concentration. 

In addition to the specificity of the monitoring method, an important requirement for the measurement of atmospheric pollutants is the accuracy of the calibration technique. The calibration procedure for the measurement of oxidants or ozone utilizes a stable and reproducible sample of dilute ozone in air. The ozone concentration of this sample is established with a reference method that is not necessarily suitable for monitoring ambient air. This reference method must agree with the scientifically accurate measurement of ozone in the calibration sample. 

Most currently used oxidant and ozone monitors need to be calibrated with a predetermined concentration of ozone in air. Regardless of the principle used to measure ambient ozone or oxidant concentrations, the primary reference standard for calibrating each monitoring device or system should be identical everywhere. This requirement remains to be achieved in practice. Up to June 1975, at least seven calibration procedures were practiced in the United States. These are listed in Table 6-5... 

In general, the direct response of plants to all oxidant pollutants has been in the foliage. In several cases of long-term exposure (grapefruit after several months of exposure to ambient oxidants) or high ozone concentration over a shorter period (apple,peach ), injury has been reported on fruit itself. 

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