Annual Average Radon Concentrations in California Residences

A study was conducted to determine the annual average radon concentrations in California residences, to determine the approximate fraction of the California population regularly exposed to radon concentrations of 4 pCI/l or greater, and to the extent possible, to identify regions of differing risk for high radon concentrations within the state. Annual average indoor radon concentrations were measured with passive (alpha track) samplers sent by mail and deployed by home occupants, who also completed questionnaires on building and occupant characteristics. For the 310 residences surveyed, concentrations ranged from 0.10 to 16 pCI/l, with a geometric mean of whole-house (bedroom and living room) average concentrations of 0.85 pCI/l and a geometric standard deviation of 1.91. A total of 88,000 California residences (0.8 percent) were estimated to have radon concentrations exceeding 4 pCI/l. When the state was divided into six zones based on geology, significant differences in geometric mean radon concentrations were found between several of the zones. Zones with high geometric means were the Sierra Nevada mountains, the valleys east of the Sierra Nevada, the central valley (especially the southern portion), and Ventura and Santa Barbara Counties. Zones with low geometric means included most coastal counties and the portion of the state from Los Angeles and San Bernardino Counties south.     

Eight-Hour Ozone Trends at Sites in Lake Michigan Ozone Nonattainment Areas

ABSTRACT

Temperature-adjusted trends in 1-hr and 8-hr ozone averages were calculated for ten sites near Lake Michigan for 1980-1995. Results show that ozone trends declined similarly according to both metrics for sites on the west side of the lake. This suggests that the factors underlying the trends were similar. These factors include, among others, ozone control programs designed to address the 1-hr standard. Thus, these control programs may have been similarly effective in moving these sites toward compliance with the 8-hr standard.     

Ozone Transport

Elevated concentrations of ozone, often above the national ambient air quality standard for photochemical oxidants, have been measured in both urban and rural areas of Connecticut. One such episode took place on June 10, 1974. Ozone levels, after stabilizing at values slightly above the standard (i.e., 80 to 110 ppb; Connecticut generated ozone concentrations), rose sharply late in the afternoon reaching concentrations as high as 310 ppb (almost 4 times the standard) in Hartford. The trajectory of the air mass, which arrived in Hartford at the time of maximum O₃ occurence, had its origin in the metropolitan New York area during the early morning rush hour on the episode day. This illustrates that the advective transport of O₃ and O₃ precursors into Connecticut from New York are probably responsible for a significant portion (approximately two-thirds) of the elevated O₃ concentrations measured throughout Connecticut on days when winds are from the south-southwest direction. The fact that peak O₃ levels occur late in the afternoon, several hours after maximum sunlight intensity, reinforces the conclusion that excessive O₃ concentrations developed as O₃ and ozone precursors were generated in the vicinity of New York City and then drifted inland into Connecticut on the afternoon sea breeze.

It appears to be unrealistic to develop a hydrocarbon control strategy for Connecticut in order to meet the photochemical oxidant ambient air quality standard when O₃ and/or ozone precursors ad-vectively transported into the State cause oxidant levels to exceed the standard. The complete cessation of all anthropogenic hydrocarbon emissions in Connecticut would not necessarily assure that the standard would be attained here. The implication is that a regional (i.e., the eastern part of the United States) hydrocarbon control strategy is needed to reduce adequately ozone formation and transport so as to allow Connecticut to meet the current oxidant standard.     

Ozone exposure

Increased tropospheric ozone concentrations cause damage to both human health and the environment. To assess the exposure of forest areas and selected tree species to ozone, it is necessary to calculate the ozone exposure distribution. The present article describes the application of an ozone interpolation model to the calculation of the ozone exposure distribution in combination with forest inventory data. The exposure of forest regions to ozone was assessed by means of an AOT40 map (accumulated ozone exposure over a threshold of 40 ppb). The calculation was performed by hourly running of the model during the summer term and accumulation of the patterns that exceeded 40 ppb. The exposure of the primary Austrian tree species to ozone can be assessed due to the spatial relation of ozone exposure and tree species patterns. This spatial relation also allows the verification of assumptions concerning ozone-related tree damage.     

Ozone decay rates in residences

In urban and suburban settings, indoor ozone exposures can represent a significant fraction of an individual's total exposure. The decay rate, one of the factors determining indoor ozone concentrations, is inadequately understood in residences. Decay rates were calculated by introducing outdoor air containing 80-160 parts per billion ozone into 43 residences and monitoring the reduction in indoor concentration as a function of time. The mean decay rate measured in the living rooms of 43 Southern California homes was 2.80 +/- 1.30 hr-1, with an average ozone deposition velocity of 0.049 +/- 0.017 cm/sec. The experimental protocol was evaluated for precision by repeating measurements in one residence on five different days, collecting 44 same-day replicate measurements, and by simultaneous measurements at two locations in six homes. Measured decay rates were significantly correlated with house type and the number of bedrooms. The observed decay rates were higher in multiple-family homes and homes with fewer than three bedrooms. Homes with higher surface-area-to-volume ratios had higher decay rates. The ratio of indoor-to-outdoor ozone concentrations in homes not using air conditioning and open windows was 68 +/- 18%, while the ratio of indoor-to-outdoor ozone was less than 10% for the homes with air conditioning in use.     

An Ozone Event in Indianapolis

There are doubts concerning the sources of the pollutant ozone in an urban location. Current control regulations,¹ for example, are based on local sources. Many studies suggest that plumes of pollutants released by upwind areas are the cause. For example, New York City has been associated with high O₃ in New England,² Chicago with O₃ in Milwaukee,³ and St. Louis with O₃ in rural Illinois.⁴ Others^5,6 have suggested the problem must be treated on a synoptic scale. In an effort to understand the problem at Indianapolis better, a series of experiments involving aircraft flights were conducted in the Indianapolis area and their results are herein reported. Specifically, a cross country flight of over 100 mi both to the northeast and southwest of Indianapolis, a vertical spiral to 28,000 ft, low level data associated with takeoff and landing of the aircraft, and ground data at four sites, are available for the afternoon of June 9,1976.     

Ozone Predictions in Atlanta,Georgia: Analysis of the 1999 Ozone Season

ABSTRACT

Ozone prediction has become an important activity in many U.S. ozone nonattainment areas. In this study, we describe the ozone prediction program in the Atlanta metropolitan area and analyze the performance of this program during the 1999 ozone-forecasting season. From May to September, a team of 10 air quality regulators, meteorologists, and atmospheric scientists made a daily prediction of the next-day maximum 8-hr average ozone concentration. The daily forecast was made aided by two linear regression models, a 3-dimensional air quality model, and the no-skill ozone persistence model. The team's performance is compared with the numerical models using several numerical indicators. Our analysis indicated that (1) the team correctly predicted next-day peak ozone concentrations 84% of the time, (2) the two linear regression models had a better performance than a 3-dimensional air quality model, (3) persistence was a strong predictor of ozone concentrations with a performance of 78%, and (4) about half of the team's wrong predictions could be prevented with improved meteorological predictions.     

Indoor Ozone Exposures

Indoor and outdoor ozone concentrations were measured from late May through October at three office buildings with very different ventilation rates. The indoor values closely tracked the outdoor values, and, depending on the ventilation rate, were 20 to 80 percent of those outdoors. The Indoor/outdoor data are adequately described with a mass balance model. The model can also be coupled with reported air exchange rates to estimate indoor/outdoor ratios for other structures. The results from this and previous studies indicate that Indoor concentrations are frequently a significant fraction of outdoor values. These observations, and the fact that most people spend greater than 90 percent of their time indoors, indicate that indoor ozone exposure (concentration × time) is greater than outdoor exposure for many people. Relatively Inexpensive strategies exist to reduce indoor ozone levels, and these could be implemented to reduce the public’s total ozone exposure.     

Ozone and grosswetterlagen

Meteorological conditions have a decisive impact on surface ozone concentrations. In this study, an empirical model is used to explain the interdependence of ozone and grosswetterlagen. Different meteorological parameters such as air temperature, global solar radiation, relative humidity, wind direction and wind speed are used. Additional nitric oxide (NO) was taken as a representative for the emission situation and ozone maximum of the preceding day in order to evaluate the development of the photochemical situation. The dataset includes data collected over a period of three years (1992–1994) from three stations outside of Munich and one in the center of Munich. All values become variables by calculating means, sums or maxima of the basic dataset consisting of half-hour means. Seasonal periodicity of data is detected with Fourier analysis and eliminated by a division method after computing a seasonal index. The dataset is divided into three different grosswetterlagen groups, depending on main wind direction. One mostly cyclonic (westerly winds), onemixed (alternating winds) and one onlyanticyclonic (easterly winds). The last is completed with one summertime group including values from April to August. Factor analysis is performed for each group to obtain independent linear variable combinations. Overall, relative humidity is the dominant parameter, a typical value indicating meteorological conditions during a grosswetterlage. Linear multiple regression analysis is performed using the factors obtained to reveal how the ozone concentrations are explained in terms of meteorological parameters and NO. The results improve from cyclonic to anticyclonic grosswetterlagen in conformance with the increasing significance of photochemistry, indicated by the high solar radiation and high temperature, and the low relative humidity and low wind speed. The explained variance r² reaches its maximum with more than 50 % of the time in Munich center. This empirical model is applicable to the forecasting of local ozone maximum concentrations with a total standard error deviation of 8.5 to 12.8 % and, if ozone concentrations exceed 80 ppb, with a standard error deviation of 5.4 to 9.5 %.     

Ozone and grosswetterlagen

Meteorological conditions have a decisive impact on surface ozone concentrations. In this study, an empirical model is used to explain the interdependence of ozone and grosswetterlagen. Different meteorological parameters such as air temperature, global solar radiation, relative humidity, wind direction and wind speed are used. Additional nitric oxide (NO) was taken as a representative for the emission situation and ozone maximum of the preceding day in order to evaluate the development of the photochemical situation. The dataset includes data collected over a period of three years (1992–1994) from three stations outside of Munich and one in the center of Munich. All values become variables by calculating means, sums or maxima of the basic dataset consisting of half-hour means. Seasonal periodicity of data is detected with Fourier analysis and eliminated by a division method after computing a seasonal index. The dataset is divided into three different grosswetterlagen groups, depending on main wind direction. One mostly cyclonic (westerly winds), one mixed (alternating winds) and one only anticyclonic (easterly winds). The last is completed with one summertime group including values from April to August. Factor analysis is performed for each group to obtain independent linear variable combinations. Overall, relative humidity is the dominant parameter, a typical value indicating meteorological conditions during a grosswetterlage. Linear multiple regression analysis is performed using the factors obtained to reveal how the ozone concentrations are explained in terms of meteorological parameters and NO. The results improve from cyclonic to anticyclonic grosswetterlagen in conformance with the increasing significance of photochemistry, indicated by the high solar radiation and high temperature, and the low relative humidity and low wind speed. The explained variance r² reaches its maximum with more than 50 % of the time in Munich center. This empirical model is applicable to the forecasting of local ozone maximum concentrations with a total standard error deviation of 8.5 to 12.8 % and, if ozone concentrations exceed 80 ppb, with a standard error deviation of 5.4 to 9.5 %.     

Ozone and urban forests in Italy

Ozone levels along urban-to-rural gradients in three Italian cities (Milan, Florence, Bari) showed that average AOT40 values at rural and suburban sites were 2.6 times higher than those determined at urban sites. However, O₃ also exceeded the European criteria to protect forest health at urban sites, even when the standards for human health protection were met. For protecting street trees in Mediterranean cities, the objectives of measurement at urban sites should extend from the protection of human health to the protection of vegetation as well. A review of forest effects on O₃ pollution and of O₃ pollution on forest conditions in Italian cities showed that it was not possible to distinguish the effect of O₃ in the complex mixture of urban pollutants and stressors. A preliminary list of tree species for urban planning in the Mediterranean area shows the average tree capacity of O₃ removal and VOC emission.     

Site Redundancy in Urban Ozone Monitoring

This article describes two statistical methods that enable air pollution control agencies to assess the effectiveness of the spatial distribution of current stationary ozone monitoring networks by providing measures of site redundancy. These methods analyze site redundancy by determining the degree to which ozone measurements at one site can be successfully predicted from data collected at other monitoring sites. The first method, the similarity (SIM) measure, calculates redundancy based on the percentage of common operational days during which two monitoring stations report similar daily maximum ozone concentrations. The second method, a modeling technique, relates site redundancy in ozone measurement to an R-squared statistic from an autoregressive model. The model uses meteorological components recorded at a central location and ozone concentrations reported by the network’s other monitoring stations. Both techniques can assist in effective allocation of limited monitoring resources and offer a statistical approach to ambient air monitoring network design. The techniques are applied to data collected at six ozone monitoring stations in Harris County, Texas, during an eight-year period in the 1980s. The methods identified two sites in the six-site network that exhibit a high degree of redundancy.     

Ozone and forests in South-Western Europe

The paper provides basic information about background, objectives and structure of O3SWE (Ozone at the permanent monitoring plots in South-Western Europe), an international co-operative project aimed at evaluating O3 concentrations, cumulative exposure, uptake and effects on forest vegetation in four countries of South-Western Europe (France, Italy, Luxenbourg, Spain and Switzerland). The project covers a total of 83 permanent plots of the EU and UN/ECE intensive forest monitoring programme and span over three years of investigation (2000-2002). The O3SWE project aims to demonstrate how, using data collected routinely in an intensive forest monitoring network, O3 exposure, flux and effects can be assessed and exceedances critically evaluated.     

Effects of Nighttime Chemistry upon the Transport of Ozone and Ozone Precursors

It has been recognized for several years that ozone in rural areas can exceed the National Ambient Air Quality Standard (NAAQS) for photochemical oxidant whirh was 0.08 ppm for one hour, not to be exceeded more than once per year. During the summer of 1973, the NAAQS was exceeded from 15 to 37% of the time at four rural monitoring sites in Maryland, Pennsylvania, Ohio, and West Virginia.¹ This is a greater violation rate than is found in many urban areas. Dimitriades and Altshuller² have enumerated four possible sources for this rural ozone: (a) transport from urban areas, (b) local photochemical generation from urban ozone precursors, (c) local photochemical generation from precursors of rural origin which may be man-made or natural, and (d) injection of stratospheric ozone into the rural area. This paper considers the chemistry pertinent to the first two of these possible sources of rural ozone, namely the long distance (overnight) transport of ozone and ozone precursors.     

Passive Sampling for Ozone

The Brigham Young University (BYU) organic sampling system (BOSS) and the high flow rate multi-system BYU organic sampling system (BIG BOSS), which use multichannel diffusion denuder sampling techniques, were both used to collect samples of atmospheric fine particulate organic material. Both systems were used at the Meadview sampling site located at the western boundary of the Grand Canyon National Park in northwestern Arizona for the Project MOHAVE summer intensive sampling program in August 1992. The concentrations of total fine particulate carbonaceous material determined by temperature programmed volatilization for BOSS collocated replicate samples were in agreement with an uncertainty of ±14%. A comparable agreement was seen between the BOSS and BIG BOSS samples. Carbonaceous material collected by the second of two sequential quartz filters was shown to have originated from organic material lost from particles during sampling. About one-half of the fine particulate organic material was lost from particles during sample collection. These semi-volatile organic compounds lost from particles during sampling were characterized by GC/MS analysis. The concentrations of n-alkanes, n-fatty acids, n-fatty methyl esters, and phthalic acid as a function of fine particulate size were obtained for compounds both retained by and lost from particles during sampling. The possible sources of fine particulate semi-volatile organic material collected at Meadview, and the particle size distribution of fine particulate organic material, n-alkanes, n-fatty acids, and n-fatty esters are discussed.     

Ozone measurements over snow

Sampling over snow surfaces to detect ozone was carried out over two winters, to validate the observations previously made by Palmer.Using the same type of ozone sensor and making concurrent measurements with other instruments, it is concluded that the reported high concentrations of ozone under clear sky conditions are probably not real, but are rather the result of instrument difficulties involving sunlight impinging on the sensing system.     

Measurement of Ozone Concentration

A method based on hourly NWS cloud amount reports is presented for developing a simple model to account for cloud cover in the determination of the nitrogen dioxide photolysis rate constant, k ₁ The model is parameterized and verified with direct UV radiometer and k ₁ measurements (vs. time of day) collected by Sickles, et al. ¹ at Research Triangle Park. Application of our model to variable cloud condition situations indicates that significant improvement in k ₁ prediction is obtained by including the influence of cloud cover. Comparison of our model with the radiative transfer calculations of Peterson⁷ indicates that the particular parameterization of k ₁ given here is most representative of average albedo and relatively heavy aerosol loading conditions. Comparison of ozone predictions using hourly averaged k ₁ and instantaneous k ₁ under conditions of varying cloud cover suggest that the errors resulting from averaging k ₁ are largest when variations in solar zenith angle are significant over the hour.     

Ozone Air Quality Models

Abstract

The field of ozone air quality modeling, or as it is commonly referred to, photochemical air quality modeling, has undergone rapid change in recent years. Improvements in model components, as well as in methods of interpreting model performance, have contributed to this change. Attendant with this rapid change has been a growing need for those developing and using air quality models and policy makers to have a common understanding of the use and role of models in the decision making process. This Critical Review highlights recent advances and continuing problem areas in photochemical air quality modeling. Emphasis is placed on the components and input data for such models, model performance evaluation, and the implications for their use in regulatory decisions.