Observed Ozone Concentrations Research Articles

Nonlinear dynamics of hourly ozone concentrations: nonparametric short term prediction

Due to inherent spatial and temporal variability of emission concentrations, influence of meteorological conditions, and uncertainties associated with initial and boundary conditions, it is very difficult to model, calibrate, and validate ozone variations from first principles. This paper describes a new procedure, based on dynamical systems theory, to model and predict ozone levels. A model is constructed by creating a multidimensional phase space map from observed ozone concentrations. Predictions are made by examining trajectories on a reconstructed phase space that applies to hourly ozone time series from the Cincinnati area. The proposed phase space model is used to make one-hour to one-day ahead predictions of ozone levels. Prediction accuracy is used as a diagnostic tool to characterize the nature, random vs deterministic, of ozone variations. To demonstrate the utility of this diagnostic tool, the proposed method is first applied to time series with known characteristics. Results for the ozone time series suggest that it can be characterized as a low-dimensional chaotic system. Then, the performance of the proposed phase space and optimum autoregressive model are compared for one-hour and one-day ahead predictions. Three performance measures, namely, root-mean-square error, prediction accuracy, and coefficient of determination yield similar results for both phase space and autoregressive models. However, the phase space model is clearly superior in terms of bias and normalized absolute error of predictions, specially for one-day ahead predictions. In addition, the ability of the proposed model to identify the underlying characteristics from a time series makes it a powerful tool to characterize and predict ozone concentrations.

Local concentrations of the tropospheric oxidants OH and O3; measurement and interpretation

Measurements of the oxidants OH and O 3 have been carried out at the Weybourne Atmospheric Observatory (WAO) in North Norfolk. These measurements are compared with model calculations and as an example one day (June 22nd, 1995) is presented. The comparison for OH shows good agreement, indicating that the applied model sufficiently describes the relevant tropospheric chemistry and that the measurement of the ancillary data provides a set which contains all the necessary information. The model further allows us to specify the contribution from the source and sink terms to the measured concentration, showing, e.g. that the observed strong decrease of the OH in the afternoon is mainly a result of changes in the source term and that, in the morning, the reaction with NO 2 is the main sink. For the observed ozone concentration a detailed calculation was made to estimate the influence of transport on the measured concentration indicating that transport contributes ca. 40% to the total sink term, and that sometimes much larger contributions are possible. The calculated net flux shows strong influences from the chemical composition of the transported air masses as well as from the strength of the transport.

Accounting for meteorological effects in measuring urban ozone levels and trends

Observed ozone concentrations are valuable indicators of possible health and environmental impacts. However, they are also used to monitor changes and trends in the sources of ozone and of its precursors, and for this purpose the influence of meteorological variables is a confounding factor. This paper examines ozone concentrations and meteorology in the Chicago area. The data are described using least absolute deviations and local regression. The key relationships observed in these analyses are then used to construct a nonlinear regression model relating ozone to meteorology. The model can be used to estimate that part of the trend in ozone levels that cannot be accounted for by trends in meteorology, and to ‘adjust’ observed ozone concentrations for anomalous weather conditions.

Seasonal cycle of C 2C 5 hydrocarbons over the Baltic Sea and Northern Finland

Measurements of C 2C 5 hydrocarbons in ambient air from a marine and a mountain site in Scandinavia are presented in relation to observed ozone concentrations. The marine site (the island of Utö) is located in the Baltic Sea about 80 km southwest of mainland Finland, while the other site (Pallas) is 900 km to the north on a fell top in a sub-arctic environment north of the Arctic Circle. The concentrations at both stations show a seasonal cycle with a winter maximum which is typical of arctic and mid-latitude areas. In spring, the concentrations decreased in steps when the air mass changed to a cleaner oceanic or arctic types after a period with the prevailing continental air mass. The decrease of concentrations in spring was further studied in terms of the concentration ratio between Utö and Pallas. For low and moderately reactive alkan es the ratio decreased steadily from March to August, indicating a long period of photochemical transformation from a winter concentration distribution to a summer one. However, for alkenes the concentrations at the northern site, compared to the more southerly one, were lower in spring and increased in summer. This suggests an emissions source that is active in summer in the vicinity of the northern terrestrial site. Isoprene and 1-butene are only observed at the pristine northern site during the growing season. The :local photochemical reactivity of the hydrocarbon mixture was estimated by calculating Propylene-Equivalent concentrations. In summer, isoprene, 1-butene, ethene, and propene comprise 50 and 80% of the total reactive mass at Utö and Pallas, respectively. The spring decrease of total reactive mass is much less compared to the total mass of light hydrocarbons. In fact, the total reactivity-scaled mass at the site north of the Arctic circle was roughly the same in April and in July, the minimum being observed in May before the beginning of the growing season. Logarithmic alkane ratios were used to estimate photochemical age, assuming OH-initiated photochemistry as the only sink process for these species. Based on the ethane and propane concentrations, the calculations gave a seasonal cycle of photochemical activity with a concomitant increase with background ozone concentrations in spring. When the calculations were made using propane and n-butane concentrations, which have a shorter lifetime, the resulting scale of photochemical histories was more regional. Ozone concentrations were higher during continental air masses compared to background ozone concentrations when the photochemical histories showed a more aged hydrocarbon composition.

Relations between Meteorology and Ozone in the Lake Michigan Region

The field program phase of the Lake Michigan Ozone Study (LMOS) took place during the summer of 1991. Observed ozone concentrations and weather variables have been analyzed for the Lake Michigan region and the eastern United States for four 1991 LMOS ozone episodes covering 21 days. It is found that all LMOS episodes are associated with large polluted regions with dimensions of 1000–2000 km, located on the western side of high pressure systems centered over the eastern United States. Consequently, the air coming into the LMOS region contains significant amounts of ozone, haze, and other pollutants advected along trajectories with anticyclonic curvature originating in upwind source regions from St. Louis, through the Ohio River valley, and into the northeast megalopolis. The local sources in the Gary-Chicago-Milwaukee region then add to this already polluted air mass, where concentrations are influenced by the strong stability of the boundary layer over Lake Michigan and the associated lake-land-breeze circulations. However, the magnitudes of ozone concentrations in the LMOS region are often quickly and significantly reduced by rain and by fronts, which are present in some portion of the domain during nearly all of the days that were studied. The portion of the urban ozone plume that is not influenced by rain and fronts is observed to be advected into rural areas at downwind distances of 100–200 km or more from Chicago, and often has concentrations higher than those in Chicago. Whether maximum concentrations are located on the western or the eastern shoreline of Lake Michigan depends on whether winds have an easterly or westerly component.

The sensitivity of regional ozone modeling to biogenic hydrocarbons

The sensitivity of regional ozone concentrations to biogenic hydrocarbons in the northeastern United States has been examined using an Eulerian grid photochemical model having a horizontal resolution of 18 km. A 6‐day period during which observed ozone concentrations exceeded 200 ppb was simulated. Detailed estimates of biogenic nonmethane hydrocarbon (NMHC) emissions were included in the model simulations. Overall, biogenic emissions were of the same order of magnitude as anthropogenic emissions. Approximately 33% of the biogenic inventory was in the form of isoprene, with the remainder of the NMHC in the form of monoterpenes and unidentified NMHC. Three model sensitivity runs were analyzed in which biogenic emissions, and then anthropogenic hydrocarbon emissions, were selectively removed from the emissions data set. Episode maximum predicted ozone concentrations were compared for each simulation, and a detailed chemical analysis was performed on two trajectories within the modeling domain. The analysis showed that the relative impact of biogenic compared to anthropogenic hydrocarbons on ozone generation varied spatially over the model domain. The biogenic influence on ozone was greatest in western and southern sections of the domain, particularly in the Ohio Valley, while the anthropogenic influence was greatest in the urbanized Northeast Corridor and industrial Great Lakes area.

Development of a regional oxidant model and application to the northeastern United States

Elevated oxidant concentrations due to the long-range transport of ozone and its precursors have been observed in many rural areas in the continental United States. The oxidation processes associated with ozone formation in the atmosphere have many important implications for regional air quality problems, such as regional haze and acid deposition. This paper describes the development and evaluation of a mesoscale photochemical air quality simulation model (RTM-III) covering the northeastern United States. The model considers an area 2080 km in the E-W direction by 1840 km in the N-S direction, with a spatial resolution on the order of 80 x 80 km, and a temporal resolution on the order of one hour. Data collected during an episode in July 1978 by the EPRI Sulfate Regional Experiment is used for testing and evaluating the model. In a comparison of hourly predictions with observations, the model predictions, with a few exceptions where local influences are suspected, generally track the measured spatial pattern and diurnal variation of ozone concentrations quite well. The correlation coefficient matched by time and location over more than 1500 pairs of hourly predicted and observed ozone concentrations is 0.7.

The effect of temperature on ozone formation in the propene/nitrogen dioxide/air system

Abstract A series of laboratory experiments were conducted to determine whether the positive correlation observed in the ambient atmosphere between ozone and temperature could, in part, be due to a temperature dependency of the photochemical smog reaction kinetics. The experiments were conducted using the propene/NO2/air system in General Motors Research Laboratories’ dynamic irradiation chamber. Over the range of temperatures investigated, 10°C to 50°C, the maximum observed ozone concentration increased with increasing temperature from 10°C to 40°C. Between 40°C and 50°C there was no further increase in ozone. In contrast, it was observed that the amount of peroxyacetylnitrate formed decreased with increasing temperature. These observations can be attributed to the temperature dependence of the thermal decomposition of peroxyacetylnitrate. At low temperatures, the increased stability of this compound makes it a sink for nitrogen dioxide; conversely, at higher temperatures, peroxyacetylnitrate is too unst...

Empirical Relationships between Observed Ozone Concentrations and Geographical Areas with Concentrations Likely to Be above 120 ppb

The extent to which existing ozone monitoring data can be used to represent concentrations outside the area immediately surrounding a monitoring station is investigated. The results should be of Interest to those who wish to define areas within which standards are likely to have been exceeded. Relationships are established between the observed second-maximum hour-average ozone concentrations and the area within which It is possible to state with reasonable probability that National Ambient Air Quality Standards (NAAQS) have or have not been exceeded. All pairs of SAROAD stations (Storage and Retrieval of Aerometric Data) separated by 500 km or less which had nearly complete annual data sets were considered for the years 1974 through 1977 to determine the probability that the NAAQS would be exceeded at one station of the pair, given station separation and the observed second-maximum hourly ozone concentration at the other station. The resulting relationship was applied to SAROAD data for 1977, and circles were drawn around each SAROAD monitoring site to show the area within which it is 90% probable that the 120 ppb NAAQS was exceeded during 1977.

Observation of stratospheric ozone layer by a XeCl laser radar

We observed the stratospheric ozone layer by a newly designed powerful laser radar using a differential-absorption technique. A discharge-pumped XeCl excimer laser with a 308-nm wavelength was used as an emitter in this system. The observed ozone concentrations in an altitude range 16–25 km are in good agreement with those measured by radiosonde. The present system is promising for the continuous monitoring of the stratospheric ozone concentration because of the simplicity of the construction.

Balloon-borne chemiluminescent measurement of NO to 45 km

MEASUREMENT of nitric oxide (NO) above an altitude of 40 km is of interest because in this region of the stratosphere >70% of the total odd nitrogen (NO+NO2+HNO3+N2O5) is thought to exist as NO, and at 45 km the NO is predicted to be approximately 90% of the total1. This measurement thus provides an important test for odd nitrogen concentrations as predicted by theoretical models for ozone chemistry. Some models show that of the total ozone destruction necessary to explain the observed ozone concentration, approximately 50–70% is due to the odd nitrogen catalytic cycles2.

Meteorological Aspects of Atmospheric Ozone as a Potential Threat to the Forest Industry of North Florida

AbstractObservations over the past 8 years showed diurnal, daily, seasonal, and yearly variations in ozone levels. Ozone concentrations were highest in the late winter, spring, and early summer, and lowest in late summer. Day‐to‐day variations were associated with changes in weather patterns. Minor increases accompanied some but not all thunderstorms and cold frontal passage. Major increases were observed with squall lines, ozone‐rich air masses, and with stagnating air masses containing air pollutants.This report compares highest observed ozone concentrations with reported damaging threshold concentrations for pine and other commercially important trees.Ozone is apparently a minimal threat to the forestry industry of North Florida at the present time. However, as air pollution increases, photochemically produced ozone in stagnating air masses may become a problem to the industry as it has in other parts of the country.