A study of the variation of urban mixed layer heights

The AERMET model is used to estimate hourly mixing heights during the Joint URBAN (2003) experiment in Oklahoma City, Oklahoma. AERMET is a simple 2-D model that requires only routine meteorological observations and an early morning atmospheric sounding to estimate convective boundary layer (CBL) growth. Estimated mixing heights are compared with observed mixing heights measured during Joint URBAN 2003. Observed CBL heights are derived from profiler data using a peak signal-to-noise ratio method. The method of deriving mixing heights from profiler data is validated using daily atmospheric sounding data. Estimated mixing heights using AERMET show good agreement with observations on days of varying temperature and cloud cover. AERMET was able to estimate the rapid boundary layer growth observed in the late morning and early afternoon hours during highly convective conditions. CBL heights of over 3000 m are observed in sounding data during the late afternoon. Estimated CBL heights of over 3000 m during the late afternoon agreed well with observations from the sounding and profiler data.     

Kinetic Sequential Sampling (KSS) System: An Automated Sampling System for Measuring Vertical Concentration Profiles of Airborne Particles

ABSTRACT

An electronically controlled lift system carrying a realtime particle monitor has been developed for sampling air sequentially, at different heights within the breathing zone. Data are automatically logged at the different receptor levels, for the determination of average vertical concentration profiles of airborne particulate matter. The system is easy to operate, portable, and easily extended to different heights or modified for use with other types of monitors (e.g., a portable CO analyzer). For measuring airborne particle concentrations, a Grimm Dust Monitor 1.104/5 was used. The results of trial runs, which were carried out indoors and in a relatively open semi-rural area, are presented, and applications of the kinetic sequential sampling (KSS) system are discussed.     

Atmospheric stability class determinations on a 481-meter tower in Oklahoma

Data from seven heights on a 481-m tower in Oklahoma are analyzed to show the variation of stability with height and time. Wind direction fluctuations at the various heights are analyzed to determine the stability class associated with horizontal dispersion and the temperature difference between pairs of heights are analyzed to determine the class associated with vertical dispersion. The Oklahoma results are compared to previously reported results obtained on a 367-m tower in South Carolina. The results from the two widely separated sites corroborate one another. The two classifying techniques at both sites show that there is a marked increase in stability a little above 100m. This result indicates that dispersion estimates for effluents from stacks taller than 100 m could readily be in error when based on observations below 100 m; the observations at the lower heights would indicate more rapid dispersion than would be indicated at effluent height.     

Prediction of fish bioconcentration factors of nonpolar organic pollutants based on molecular connectivity indices.

The relationship between bioconcentration factors and molecular connectivity indices was investigated. A regression model was developed using 80 measured BCFs of nonpolar organic pollutants. The five topological parameters used were 1 chi, 2 chi, 3 chi c, 0 chi v and 2 chi v. Modified jackknife tests were applied to examine the robustness of the model by repeatedly removing a set of or a class of compounds from the database. The model was compared with one using Kow as an independent parameter. The mean absolute errors for the 80 compounds studied were 0.288 and 0.302 log-unit for the two models, respectively.     

An analysis of the frequency distribution of sodar derived mixing heights classified by atmospheric stability

SODAR has been used to determine hourly mixing heights at a site in Central Scotland for the period May 1976–April 1977. Atmospheric stabilities have also been determined for each hour, and frequency distributions of mixing heights classified by atmospheric stability have been derived. Some uses and applications of the results are discussed, particularly in terms of estimating the frequency of occurrence of peak concentrations.     

Mixing height—an inconsistent indicator of potential air pollution concentrations

The correlation between mixing height and air pollution levels was found to be inconsistent. Mixing height had a lower correlation to the maximum oxidant concentration than other parameters such as temperatures at different heights, the previous day's oxidant concentration, height and temperature of the inversion base and top, geopotential heights and pressure gradient. Mixing height also had a lower correlation with the maximum CO concentration than other parameters, including the inversion base height, the previous day's CO concentration, temperatures at different heights, pressure gradients and geopotential heights. Low correlations between mixing height and air pollution levels may be because:

• 1.(1) there is a greater variation in mixing height in time and space than is generally thought;
• 2.(2) the standard calculation of mixing height does not give an accurate estimation of the height to which pollutants are dispersed or
• 3.(3) air pollutants may have had insufficient time to disperse to the mixing height. When empirically derived statistical models are used to predict air pollution levels, failure to include mixing height as a potential predictor will probably not degrade the quality of the model.

     

Dependence of the Wind Profile Power Law on Stability for Various Locations

Recent environmental regulations have increased the need for construction of meteorological towers at power generation facilities. Due to practical and economic considerations, tower heights are usually lower than effluent release heights. At heights where wind speed data are not available, the wind speed is usually estimated from the measured wind speed using the %th wind profile power law and assuming neutral stability conditions. This study examines published data for many locations and shows that the %th wind profile power law is often unrepresentative of actual conditions because the degree of variation of wind speed with height depends greatly on atmospheric stability. The frequency of neutral stability conditions also varies appreciably by site. These two considerations are especially important in dispersion models which extrapolate wind speed at stack height from low level wind speed data.     

Numerical Modeling of the Thermal Boundary Layer Near a Synthetic Crude Oil Plant

Production from the world’s largest tar sands plant began in July 1978. Under the permit to construct the plant, Syncrude Canada Ltd. is permitted to emit 287 long tons of SO₂/day as long as Alberta’s Clean Air Regulations are not Violated. In order to predict such violations for emission control purposes, it is important to know the diurnal variation of the thermal boundary layer (TBL) height. In this paper, a numerical model for the prediction of TBL height as a function of time of day is given based on the solution of appropriate conservation equations relating both the heat flux and the temperature jump across the inversion layer to the height of the TBL. The resulting equations are solved by the Runge-Kutta method. The model is tested against the field data collected as part of a base-line data acquisition program. A comparison is also made of two different methods (kink method and conventional method) to calculate thermal boundary heights from the mini-sonde data. Problems in the use of the results of TBL heights using these two methods for predicting pollution potential near the plant are also discussed.     

Relationship of properties of polycyclic aromatic hydrocarbons to sequestration in soil.

A study was conducted to determine whether the sequestration of 21 polycyclic aromatic hydrocarbons (PAHs) in soil was correlated with their properties. From 22 to 58% of the PAHs was not extracted with n-butanol after their addition to soil. After 28 days of aging, the percentage of the PAHs remaining in the soil increased to 47-77%; however, nearly all of each compound was recovered by Soxhlet extraction. Correlations were based on the amounts of aged compound extracted with butanol. Properties of compounds used in the correlations included Kow, molecular length and molecular-connectivity indices (MCIs). No one property, including log Kow, resulted in an R2 value greater than 0.26. A chain MCI (2 chi vCH) together with log Kow or a first-order MCI (1 chi) resulted in R2 values of 0.49 and 0.54, respectively. The data suggest that the properties tested are not important to predicting the sequestration of PAHs in soil.     

The impact of trajectory starting heights on the MURA trajectory source apportionment (TSA) method

Trajectory source apportionment (TSA) methods have been used in many research projects to attempt to identify the sources of pollution. Hybrid Single Particle Lagrangian Integrated Trajectories (HYSPLIT) is a popular model for use in various TSA methods. One of the options in this model is to choose a starting height. Very little research is available to assist a user in making this choice. This paper evaluates starting heights of 10, 50, 100, 250, and 500 m on the accuracy of the Multi-Receptor (MURA) method using artificial sources for three different simulations. It was found that using ensembles of trajectories in the MURA method appear to average out most of the biases found from different trajectory starting heights up to the 500 m tested.     

Transport and dispersion during wintertime particulate matter episodes in the San Joaquin Valley, California

Data analysis and modeling were performed to characterize the spatial and temporal variability of wintertime transport and dispersion processes and the impact of these processes on particulate matter (PM) concentrations in the California San Joaquin Valley (SJV). Radar wind profiler (RWP) and radio acoustic sounding system (RASS) data collected from 18 sites throughout Central California were used to estimate hourly mixing heights for a 3-month period and to create case studies of high-resolution diagnostic wind fields, which were used for trajectory and dispersion analyses. Data analyses show that PM episodes were characterized by an upper-level ridge of high pressure that generally produced light winds through the entire depth of the atmospheric boundary layer and low mixing heights compared with nonepisode days. Peak daytime mixing heights during episodes were -400 m above ground level (agl) compared with -800 m agl during nonepisodes. These episode/nonepisode differences were observed throughout the SJV. Dispersion modeling indicates that the range of influence of primary PM emitted in major population centers within the SJV ranged from -15 to 50 km. Trajectory analyses revealed that little intrabasin pollutant transport occurred among major population centers in the SJV; however, interbasin transport from the northern SJV and Sacramento regions into the San Francisco Bay Area (SFBA) was often observed. In addition, this analysis demonstrates the usefulness of integrating RWP/RASS measurements into data analyses and modeling to improve the understanding of meteorological processes that impact pollution, such as aloft transport and boundary layer evolution.     

Maximum Ground-Level Concentrations with Downwash—Analysis

ABSTRACT

Equations derived previously for critical downwind distance x , wind speed u , and plume rise z , the values that produce maximum ground-level concentrations (MGLC) X_c under downwash conditions, have been solved. Tables of %_c, x_c, u_c, and z_c, and graphs of the relationships among u_c and z_c for a range of stack heights h_s, and building heights h_b, are presented. Results for two types of sources— a turbine and a reciprocating engine—are discussed. Some comparisons are made to the U.S. Environmental Protection Agency's (EPA) SCREEN3 model.     

Vertical distribution of atmospheric trace metals and their sources at Mumbai,India

In the modern times, due to high rise multistoried buildings, especially in metropolitan cities, the habitable heights have changed from the ground floor level to higher levels. Present study is focused at generating a vertical profile of aerosols and the elemental concentrations in an un-inhabited environment in the envelope of a high rise building in a relatively clean environment of Mumbai. This can serve as a base line information to study the vertical profile in polluted areas like city centres and street canyons. Suspended particulate matter (SPM) at different floors and particle size distribution of aerosols at 12th floor (top floor) have been estimated. Thirteen trace metals, namely Ca, Cd, Cr, Cu, Fe, K, Li, Mg, Mn, Na, Ni, Pb and Zn were estimated in the SPM and in size separated aerosols, monitored over a period of 2 months. An attempt is also made to identify the sources of SPM at different heights using correlation matrix and factor analysis. The study indicates insignificant differences in the concentration levels of SPM and trace metals at different heights, when compared to the first floor level in the height range of 4.5–37.5 m. Of the 13 measured elements at the first floor level, Na (64.4%) and Ca (13.9%) constituted the dominant fractions followed by Fe (8.3%), Mg (5.7%), K (3.1%), Al (2.3%), Zn (1.3%) and Pb (0.5%). A similar distribution was also found for the 12th floor level (top floor). Factor analysis carried out using the measured elements, identified soil and sea salt spray as the main sources for the SPM at all the floors monitored.     

Large-Scale Weather Influences on Community Air Pollution Potential in the United States

This paper describes the large-scale weather features that typically are associated with relatively rapid and slow atmospheric dispersion. Specific examples for some well-known air pollution incidents are illustrated and discussed. Particular attention is paid to the features of quasi-stagnating anticyclones, the typical weather system associated with persistent and extensive areas of sluggish dispersion. On the large scale, the basic quantitative parameters of dispersion over urban areas are the mixing height and the wind speed averaged through that height. These parameters are defined and discussed. Mean morning and afternoon mixing heights and wind speeds are presented for four locations across the United States, illustrating their diurnal, seasonal, and spatial variations. Also for these four locations, data are given on the climatological occurrence of periods during which critical values of the basic parameters were not exceeded. The spatial distributions of mixing heights and average wind speeds during a well-documented air pollution episode are presented.     

Developmental dental defects in children exposed to PCBs in eastern Slovakia

The effects of long-term exposure to polychlorinated biphenyls (PCBs) on developmental dental defects of deciduous and permanent teeth in children in eastern Slovakia, where PCBs from a chemical plant manufacturing Delors contaminated the surrounding district were evaluated. Four hundred and thirtytwo children, lifelong residents, aged 8-9 years were examined. Children's caries susceptibility and gingival health was assessed by standard dental indices, and developmental enamel defects by the FDI index. Data from the PCBRISK project data set and questionnaires completed by the parents provided information on exposure and various confounding factors. The proportion of teeth with different types and extensions of developmental enamel defects correlated with serum PCB concentration. The proportion of deciduous teeth affected with enamel defects was significantly higher in higher exposed children (chi(2)=8.35; p=0.03) according to their serum PCB concentration (group 0: <200; group 1: 200-600; group 2: >600 ng PCBs g(-1) serum lipids). The proportion of permanent teeth affected with any enamel defect was significantly higher in higher exposed children (chi2=7.237; p=0.027). Furthermore, the extent of the enamel defects was also greater (chi2=10.714; p=0.005). In multivariate linear regression analysis PCB exposure was significantly related to developmental enamel defects of permanent teeth only. No associations between PCB exposure and caries susceptibility, gingival health or number of teeth were observed. This study demonstrated a dose-response relationship between PCB exposure and developmental enamel defects of permanent teeth in children, the evidence for deciduous teeth was not conclusive.     

An empirically tractable model of optimal oil spills prevention in Russian sea harbours

Based on previous theoretical work by Gottinger (1997, 1998), we propose a simple model of optimal monitoring of oil-related activities in harbour areas that is suitable for empirical estimation within the Russian— Ukrainian context, in spite of the poor availability of data in these countries. Specifically, the model indicates how to best allocate at the steady state a given monitoring budget between different monitoring activities. An approximate analytical solution to the optimisation problem is derived, and a simple procedure for estimating the model on the basis of the actually available data is suggested. An application using data obtained for several harbours of the Black and Baltic Seas is given. It suggests that the current Russian monitoring practice could be much improved by better allocating the available monitoring resources.     

Flue gas discharge from cooling towers. Wind tunnel investigation of building downwash effects on ground-level concentrations

German power plants are required to meet new emission standards which limit the maximum sulfur dioxide (SOs) concentration in flue gas discharges to 400 mg m⁻³. To achieve this level of reduction in SO₂ concentration, wet scrubbing is necessary for large plants using lignite or hard coal.Wet scrubbing results in a significant reduction in the flue gas temperature leading to low effective stack heights. Instead of using stack gas reheating to achieve the plume rise necessary to satisfy local environmental standards, it was proposed to discharge the scrubbed flue gas from the existing natural-draft cooling towers (NDCT). This method should be effective in reducing local ground-level concentrations since NDCT-plumes are typically very buoyant (densimetric Froude number below 1 ) and normally reach considerable heights of rise. Only under strong wind conditions does the situation reverse itself. For such strong winds, the NDCT-plume is subject to tower and building downwash with the possibility of unacceptably high ground-level concentrations.For a 2700 MW_e lignite-fired power plant near Cologne, a wind tunnel study was carried out to investigate the effects of tower and building downwash effects on the ground-level concentrations of SO₂ produced by discharging the scrubbed flue gas from the natural-draft cooling towers. Also, a comparison was made between the ground-level concentrations produced by the cooling tower discharge method and those produced by a traditional stack. It was found that for low and intermediate wind speeds, the groundlevel concentrations are lower for the case of the cooling tower discharge. Only for strong winds, which occur only very rarely at most German sites, did the conventional stack discharge appear to be superior.     

Intercomparison of nocturnal mixing height estimate methods for urban air pollution modelling

One of the most important meteorological input parameters for three-dimensional photochemical air pollution models is the mixing height h, which has a strong influence on the shape and intensity of the vertical diffusivity K_z and, as a consequence, on ground-level air concentrations of primary and secondary pollutants. A number of indirect algorithms for the estimate of h in nocturnal, stable conditions, when the mixing is dominated by mechanical turbulence, are reviewed and compared with mixing heights derived from wind (SODAR) and temperature (RASS) profiles measured in the Milan urban area during spring and summer 1996. Mixing heights derived from temperature soundings correlate positively with those derived from wind soundings only when a stable layer is superimposed to a quasi-adiabatic layer, while the correlation is very weak in the presence of a ground-based inversion. In general, indirect algorithms perform very poorly if compared with RASS-based estimates, and reasonably well if compared with SODAR-based estimates. Among the others, Benkley and Schulman (1979, Journal of Applied Meteorology 18, 772–780) method, which makes use of wind speed observed at 10 m height, and Nieuwstadt (1984, Boundary-Layer Meteorology 30, 31–55), which makes use of friction velocity and Monin–Obukhov length, give the best results.     

Effective pollutant emission heights for atmospheric transport modelling based on real-world information

Emission data needed as input for the operation of atmospheric models should not only be spatially and temporally resolved. Another important feature is the effective emission height which significantly influences modelled concentration values. Unfortunately this information, which is especially relevant for large point sources, is usually not available and simple assumptions are often used in atmospheric models. As a contribution to improve knowledge on emission heights this paper provides typical default values for the driving parameters stack height and flue gas temperature, velocity and flow rate for different industrial sources. The results were derived from an analysis of the probably most comprehensive database of real-world stack information existing in Europe based on German industrial data. A bottom-up calculation of effective emission heights applying equations used for Gaussian dispersion models shows significant differences depending on source and air pollutant and compared to approaches currently used for atmospheric transport modelling.     

Evaluation of secondary organic aerosol formation in winter

Three different methods are used to predict secondary organic aerosol (SOA) concentrations in the San Joaquin Valley of California during the winter of 1995–1996 [Integrated Monitoring Study, (IMS95)]. The first of these methods estimates SOA by using elemental carbon as a tracer of primary organic carbon. The second method relies on a Lagrangian trajectory model that simulates the formation, transport, and deposition of secondary organic aerosol. The model includes a recently developed gas–particle partitioning mechanism. Results from both methods are in good agreement with the chemical speciation of organic aerosol during IMS95 and suggest that most of the OC measured during IMS95 is of primary origin. Under suitable conditions (clear skies, low winds, low mixing heights) as much as 15–20 μg C m⁻³ of SOA can be produced, mainly due to oxidation of aromatics. The low mixing heights observed during the winter in the area allow accumulation of SOA precursors and the acceleration of SOA formation. Clouds and fog slow down the production of secondary compounds, reducing their concentrations by a factor of two or three from the above maximum levels. In addition, it appears that there is significant diurnal variation of SOA concentration. A strong dependence of SOA concentrations on temperature is observed, along with the existence of an optimal temperature for SOA formation.