Warren B. Johnson

An Urban Diffusion Simulation Model For Carbon Monoxide

A relatively simple Gaussian-type diffusion simulation model for calculating urban carbon monoxide (CO) concentrations as a function of local meteorology and the distribution of traffic is described. The model can be used in two ways: (1) in the synoptic mode, in which hourly concentrations at one or many receptor points are calculated from historical or forecast traffic and meteorological data; and (2) in the climatological mode, in which concentration frequency distributions are calculated on the basis of long-term sequences of input data. For model evaluation purposes, an extensive field study involving meteorological and air-quality measurements was conducted during November-December 1970 in San Jose, Calif., which has an automated network to provide traffic data throughout the central business district. Model refinements made on the basis of the data from this experimental program include the addition of a street-canyon submodel to compensate for the important aerodynamic effects of buildings on CO c...

Tropospheric ozone: Concentrations and variabilities in clean remote atmospheres

Abstract Analysis of long-term ozone (O 3 ) data collected at remote sites between latitudes 19°N and 48°N is complemented by aircraft data to support the conclusion that a significant reservoir of ozone is present in the troposphere. Evidence suggests that this O 3 reservoir is predominantly of stratospheric origin and that photochcmical oxidation processes resulting in O 3 production from HCs (including CH 4 ), CO and NO x of natural origin do not contribute significantly to the net O 3 balance in this reservoir. It is found that the predominant source of tropospheric O 3 is due to injections from the stratosphere. The important sinks are O 3 loss at and near the earths surface and to a less certain degree gas phase photolytic destruction. The possibility that natural precursors produce O 3 , at a rate that roughly offsets the gas phase photolytic destruction, can not be ruled out. This tropospheric O 3 shows a distinct seasonal variation, with a maximum in the spring when 1-h O 3 concentrations can approach or exceed 80 parts per billion (ppb). Year to year variations can be important; for example, at Mauna Loa the hourly averaged O 3 concentrations exceeded 80 ppb 1.6% of the days in 1975 and 0% of the days in 1974. No average diurnal variation of O 3 is observed throughout the year within this reservoir. Because O 3 from this reservoir is mixed downward toward the surface under convective atmospheric conditions, the achievement of a yearly 1-h O 3 standard of 80 ppb may be impossible. Analysis of atmospheric data also indicates that the mean residence time of O 3 in the troposphere is long (≈4 months), while that of NO x , is much shorter (0.4–2 days) than the hitherto accepted value of 8–10 days.

Stratospheric ozone in the lower troposphere —I. Presentation and interpretation of aircraft measurements

Abstract The United States has instituted a number of air pollution regulations to control ozone, including an air quality standard for oxidants of 120 ppb for one hour. Accordingly, there is considerable interest in determining the magnitude of the natural (i.e. nonanthropogenic) component of ozone concentration near the ground, much of which is generally believed to come from the stratosphere. Toward this end, an extensive program of aircraft measurements of tropospheric ozone originating from the stratosphere was carried out over the Central U.S. in spring and fall 1978. On 10 of these flights, the vertical structure of stratospheric ozone intrusions was well mapped by aircraft penetrations at several altitudes extending between 2 and 8 km above sea level (ASL) in the southern portions of tropospheric low-pressure troughs. The field measurements show that stratospheric ozone intrusions into the troposphere occur more frequently than earlier studies had indicated. Ozone intrusions were found in virtually every trough, regardless of intensity, within which suitable measurements were taken. A close relationship was found between: 1. (1) maximum ozone concentrations in the intrusion; and 2. (2) trough intensity as characterized by maximum wind speed at 300 mb (approximately 10 km ASL). The intrusions typically are characterized by peak ozone concentrations at higher altitudes (6–8 km ASL) in the range of 240–400 ppb, diminishing to 100–200 ppb at lower altitudes as mixing with surrounding air occurs. Measured concentrations during spring were almost twice as high as those measured during fall, but the intrusion structures were very similar during both seasons. The data show that stratospheric ozone intrusions are typically 100–300 km wide in the crosswind direction, are several hundreds of kilometers long, and can be tracked down at least as far as the top of the atmospheric boundary layer (about 2 km ASL). Possible mechanisms for downward transport within the boundary layer include normal convective mixing, organized convection associated with cloud and precipitation processes, and organized downward motion within frontal zones.

Stratospheric ozone in the lower troposphere. II: Assessment of downward flux and ground-level impact

Abstract Aircraft measurements of four stratospheric O3-intrusion events (two during spring and two during fall) are used in conjunction with concurrent meteorological analyses to estimate the downward 03 flux in the upper and lower troposphere. The aircraft measurements used are among those reported earlier in Part I of this paper (Johnson and Viezee, 1981). The calculated upper tropospheric fluxes for the four cases show good agreement with earlier estimates by Danielsen and Mohnen (1977) of O3 fluxes associated with tropopause folding events. The estimated lower-tropospheric O3 fluxes for the two spring events and for one fall event suggest that more than half of the O3 mass injected into the upper troposphere by these stratospheric intrusions is probably mixed and diluted into the troposphere above 700 mb (3 km ASL). Large, direct impacts of stratospheric O3 intrusions at ground-level are thus unlikely. A review and analysis of the limited number of published observations of high O3 in stratospheric intrusions, and of anomalously high O3 at ground level attributed to stratospheric intrusions, also suggests that direct ground-level impacts may be infrequent (less than 1 per cent of the time), and most likely are associated with O3 concentrations (v/v) of 100 ppb or less. Additional observational studies are required to conclusively quantify the ground-level impact of stratospheric O3.

The impact of stratospheric ozone on tropospheric air quality

A background of ozone (O3), principally of stratospheric origin, is present in the lower free troposphere. Typical mean O3 levels of 50 ppb, 40 ppb, and 30 ppb are encountered here in spring, summer, and fall, respectively. Maximum hourly O3 concentrations which are twice these mean values can be expected. Ozone from the free troposphere is routinely brought down to ground level under turbulent atmospheric conditions. Deep and rapid Intrusions of stratospheric air into the lower troposphere are associated with low-pressure troughs and occur regularly. In the mid troposphere, O3 levels as high as 300 ppb are found within these intrusions. Observational data showing these intrusions, containing high O3 concentrations, to directly reach ground level are currently lacking. Over the United States, an intrusion was present aloft on 8 9% of the days in 1978. The frequency, however, is somewhat reduced in summer and a northward movement is evident. During 1978, no intrusion occurred south of 30°N between June and...

LONG TERM REGIONAL PATTERNS AND TRANSFRONTIER EXCHANGES OF AIRBORNE SULFUR POLLUTION IN EUROPE

Abstract This paper reports on progress to date of an ongoing effort to develop, evaluate and apply a European Regional Model of Air Pollution (EURMAP). This model is capable of calculating longterm (monthly, seasonal and/or annual) averages of the contributions from SO 2 in individual emittor countries to SO 2 and SO 4 2− concentrations, dry deposition and wet deposition in receptor countries. The model covers all of western and central Europe, a geographical area 2100 km × 2250 km in size. A trajectory-type approach is used, which involves the tracking of pollutant ‘puffs’ released from each emissions cell in an extensive 32 × 36 grid. Meteorological data in the form of wind and precipitation values from some 45 upper-air and 535 surface stations are input at 6-hourly intervals for use in the calculations of puff transport and wet deposition. A wet deposition coefficient is used that depends upon precipitation rate. The preliminary model has been used to calculate annualized as well as monthly mean maps for January, April, July and October 1973 of SO 2 and SO 4 2− concentration, dry deposition and wet deposition patterns resulting from SO 2 emissions in 13 countries in western and central Europe. The dry and wet deposition patterns are presented, along with values of calculated international exchanges of SO 2 and SO 4 2− wet and dry deposition among these various countries. The EURMAP results are compared with those from Fishers (1975) model and the LRTAP model (Ottar, 1978; OECD, 1977). In many (but not all) respects the results from the three models are similar. The possible reasons for the differences revealed by this comparison are examined.

Lidar study of the keystone stack plume

A lidar study of the dispersion of the effluent from the tall (245-m) stacks of Keystone Generating Station in western Pennsylvania was conducted with the aid of two field experiments in May and October 1968. The observations, which were mostly obtained during stable conditions in the morning hours, reveal in detail the important plume characteristics that must be included in a realistic diffusion model for plumes from tall stacks: 1. (1) fanning and tilting due to wind veering with height. 2. (2) fumigation, which brings high concentrations to ground level in a pattern which, because of the tilting, progresses with time from the left to the right of the plume looking downwind. 3. (3) plume trapping by elevated stable layers. A comparison between the predictions of the Briggs/ASME plume rise formula and the lidar observations for 17 cases when temperature profiles were available gave a mean absolute difference of 30 m. A secondary experiment involving two sets of lidar plume measurements when the electrostatic precipitators at the power plant were all and half in operation, furnished estimates of 86 and 97 per cent for the precipitator efficiency on two separate days, compared with the rated value of 99 per cent. To investigate the potential of lidar for making quantitative measurements, a sample attenuation-corrected cross section of absolute mass concentration was computed on the basis of Mie scattering theory and independent particle size measurements. The integrated mass per unit plume length represented by this cross section was 680 gm−1, compared to 875 g m−1 calculated from the power-plant data and wind speed.

Interregional Exchanges of Air Pollution: Model Types and Applications

Regional scale air quality simulation models covering spatial scales of thousands of kilometers are finding increasing applications in studies of acid deposition and other air pollution problems. The purpose of this paper is to familiarize the nonexpert with the characteristics of the major types of interregional air quality models currently in use: Eulerian grid, statistical trajectory, and Lagrangian trajectory. The basic features, advantages, and disadvantages of each of these modeling approaches are summarized, as are the important limitations and problems associated with interregional modeling in general. Typical applications are illustrated using examples from the use of a representative Lagrangian trajectory model, ENAMAP, over the eastern North American area.

Lidar Applications in Air Pollution Research and Control

The fundamental capabilities and limitations of the lidar (laser radar) in observing particulate concentrations in the atmosphere are discussed. The advantages of the lidar technique stem from its ability to obtain measurements remotely and at a high density in space and time. The quantitative application of the technique is limited by the accuracies with which: (1) the separate effects upon the return signal of back-scatter and attenuation may be identified; and (2) the optical parameters may be related to the characteristics of the aerosol. The main areas of utility for lidar in air pollution research and control are: (1) to observe the structure and height of mixing layers; (2) to measure the transport and diffusion of plumes or clouds of particulates; and (3) to remotely determine smoke-plume opacity. These applications are briefly reviewed and exemplified.

Analysis of Multiwavelength Observations of Optical Scintillation

Results are presented from an experimental study of the effects of wavelength, range, and thermal turbulence intensity on the laser scintillation magnitude, represented by the log-intensity standard deviation, sigma. During the first phase of the study, intensity fluctuations at 0.6328 microm were measured over a nearground horizontal path for six ranges out to 7.6 km. Similar measurements were made during the second phase at four ranges out to 2.5 km for three wavelengths: 0.4880 microm, 0.6328 microm, and 1.064 microm. A 5-mm diam receiver aperture was used in all cases. During both phases, concurrent measurements of the refractive-index-structure function C(n) were obtained. It was observed that the measured scintillation (sigma(m)) at 0.6328 microm reached a mean maximum of 1.05 when the theoretical Tatarski value (sigma(t)) was 2.5 and then decreased at larger sigma(t) to a value about 0.5, where the scintillation showed evidence of leveling off. The mean maximum scintillation at 0.4880 microm is 1.09, and at 1.064 microm it is 0.82; the ratios of the maxima are well approximated by the minus seven-twelfths power of the wavelength. At large sigma(t) values, the scintillation depends only slightly on wavelength.