Evaluating the performance of regional-scale photochemical modeling systems: Part I—meteorological predictions

In this study, the concept of scale analysis is applied to evaluate two state-of-science meteorological models, namely MM5 and RAMS3b, currently being used to drive regional-scale air quality models. To this end, seasonal time series of observations and predictions for temperature, water vapor, and wind speed were spectrally decomposed into fluctuations operating on the intra-day, diurnal, synoptic and longer-term time scales. Traditional model evaluation statistics are also presented to illustrate how the method of spectral decomposition can help provide additional insight into the models’ performance. The results indicate that both meteorological models under-represent the variance of fluctuations on the intra-day time scale. Correlations between model predictions and observations for temperature and wind speed are insignificant on the intra-day time scale, high for the diurnal component because of the inherent diurnal cycle but low for the amplitude of the diurnal component, and highest for the synoptic and longer-term components. This better model performance on longer time scales suggests that current regional-scale models are most skillful for characterizing average patterns over extended periods. The implications of these results to using meteorological models to drive photochemical models are discussed.     

Comparison of an open path differential optical absorption spectroscopy system and a conventional in situ monitoring system on the basis of long-term measurements of SO2, NO2, and O3

A field-based intercomparison study was conducted to evaluate the performance of a line-integrating monitoring technique (a commercial differential optical absorption spectroscopy, DOAS, system by Opsis AB, Sweden) in concert with a conventional in situ monitoring technique (MACSAM-2 (or MS2) system, Japan). In the course of our study, the mixing ratios of three trace gases including SO₂, NO₂, and O₃ were measured routinely from the Ban Po district of Seoul during a 13 month period (June 1999–August 2000). The data obtained from two different systems were used to evaluate various aspects of DOAS performance. The differences in the observed mixing ratios between two techniques, if assessed in terms of the percent difference (PD) values between different data sets, were in general rather compatible not only among different species but also as a function of varying time scale. The differences in the measured mixing ratio between the two systems were also examined statistically using linear regression analysis. Results of the regression analysis indicated the existence of significant correlations among all trace gases monitored, confirming the strong compatibility between the two systems. The effects of meteorological factors on the DOAS performance were also examined through investigation of the mixing ratio differences between two systems and the concurrently determined environmental parameters. According to our analysis, it is concluded that the level of agreement between the two systems can be affected by the variations in the spatial mixing conditions. Although some uncertainties remain to be resolved, our preliminary attempts to evaluate an open path monitoring technique clearly demonstrated that consideration of meteorological conditions may be required to properly assess the DOAS performance due to its capacity to cover spatial scale over the open path length.     

On the relationship between acid rain and cloud type

Spanish European Monitoring and Evaluation Programme (EMEP) stations were selected to relate acid rain episodes with the meteorological structure that caused the rainfall during a 5-year period. A principal component analysis (PCA) was used to determine the origin of major ions (SO4(2-), NO3-, Cl-, Ca2+, K+, Mg2+, and Na+) in the rainwater. In addition, the meteorological origin of the rain was identified. Previous works suggested a relationship between acid rain and storm convective clouds. However, statistical analyses of pH values show that only the short-lived convective phenomena may cause acid rain in Spain. In fact, rain generated by fronts and that related to long-lived convective systems is neutral or even slightly basic. Results suggest that the acid rain might be related to the meteorological time scale instead of to the cloud type.     

上海地区气溶胶特征及MODIS气溶胶产品在能见度中的应用

利用气象站点能见度的历史资料和美国国家宇航局的MODIS卫星遥感手段获取10 km×10 km分辨率的气溶胶光学厚度(AOD)资料,建立二者的季节平均关系,得到了上海地区季节变化的气溶胶标高,并利用标高数据和AOD的季节分布,反演出上海地区季节变化的区域能见度分布,研究了近地层大气气溶胶与地面能见度的关系,分析了上海地区AOD的特征及能见度的时空分布特征.结果显示:上海地区冬春季平均能见度较差,外环线以内能见度在10 km以下;低能见度中心分布明显.     

A review of statistical methods for the meteorological adjustment of tropospheric ozone

A variety of statistical methods for meteorological adjustment of ozone have been proposed in the literature over the last decade for purposes of forecasting, estimating ozone time trends, or investigating underlying mechanisms from an empirical perspective. The methods can be broadly classified into regression, extreme value, and space–time methods. We present a critical review of these methods, beginning with a summary of what meteorological and ozone monitoring data have been considered and how they have been used for statistical analysis. We give particular attention to the question of trend estimation, and compare selected methods in an application to ozone time series from the Chicago area. We conclude that a number of approaches make useful contributions to the field, but that no one method is most appropriate for all purposes and all meteorological scenarios. Methodological issues such as the need for regional-scale analysis, the nonlinear dependence of ozone on meteorology, and extreme value analysis for trends are addressed. A comprehensive and reliable methodology for space–time extreme value analysis is attractive but lacking.     

Artificial neural network for the identification of unknown air pollution sources

Artificial neural networks (ANN), whose performances to deal with pattern recognition problems is well known, are proposed to identify air pollution sources. The problem that is addressed is the apportionment of a small number of sources from a data set of ambient concentrations of a given pollutant. Three layers feed-forward ANN trained with a back-propagation algorithm are selected. A test case is built, based on a Gaussian dispersion model. A subset of hourly meteorological conditions and measured concentrations constitute the input patterns to the network that is wired to recover relevant emission parameters of unknown sources as outputs. The rest of the model data are corrupted adding noise to some meteorological parameters and we test the effectiveness of the method to recover the correct answer. The ANN is applied to a realistic case where 24 h SO₂ concentrations were previously measured. Some of the limitations of the ANN approach, together with its capabilities, are discussed in this paper.     

Traffic congestion and ozone precursor emissions in Bilbao (Spain)

GOAL. SCOPE. BACKGROUND: In urban environments, the measured levels of ozone are the result of the interaction between emissions of precursors (mainly VOCs and NOx) and meteorological effects. In this work, time series of daily values of ozone, measured at three locations in Bilbao (Spain), have been built. Then, after removing meteorological effects from them, ozone and traffic data have been analyzed jointly. The goal was to identify traffic situations and link them to ozone levels in the area of Bilbao. METHODS: To remove meteorological effects from the selected ozone time series, the technique developed by Rao and Zurbenko was used. This is a widely used technique and, after its application, the fraction obtained from a given ozone time series represents an ozone forming capability attributable to emissions of precursors. This fraction is devoid of any meteorological influence and includes only the apportion of periodicities above 1.7 years. In the case of Bilbao, the ozone fractions obtained at three locations have been compared on that time scale with traffic data from the area. RESULTS AND DISCUSSION: For the 1993-1996 period, a regression analysis of the ozone and traffic fractions due to periodicities above 1.7 years (long-term fractions), shows that traffic is the main explanatory factor for ozone with R2 ranging from 0.916 to 0.996 at the three locations studied. Analysis of these longterm fractions has made it possible to identify two traffic regimes for the whole area, associated to different profiles of ozone forming capability. The first one favors low ozone forming capability, and is associated with a situation of fluent traffic. The second one shows high ozone forming capability and represents congestion. Joint analysis of raw data of ozone and traffic do not show any clear pattern due to the strong masking effects that seasonal-meteorological effects (mainly radiation) have on the measured ozone signal. If only immission data of ozone are available, as in this case, a comparison between ozone and traffic can only be made on the long-term time scale, since that is the only fraction embedded in the ozone time series that can exclusively be attributed to emissions of precursors. This fact stresses the need to study the different fractions embedded in the time series of ozone measured levels separately. CONCLUSION: Though the coefficients obtained in the regression are only valid for the 1993-1996 period, these traffic regimes represent long-term targets (congestion or fluent traffic) that can inspire policies for a joint management of the traffic and pollution by ozone in the area of Bilbao beyond that period. RECOMMENDATIONS AND OUTLOOK: The results of this work show the need of a joint management of ozone and traffic in Bilbao. Since an accurate knowledge of traffic was not available, the use of emission factors to relate traffic and actual ozone levels has not been possible. For this reason, this study has focused on the long-term fractions of traffic and ozone. In the future, if a more accurate knowledge of traffic is available, it will be possible to find relationships between traffic and ozone on all time scales.     

On the Relationship between Acid Rain and Cloud Type

Abstract

Spanish European Monitoring and Evaluation Programme (EMEP) stations were selected to relate acid rain episodes with the meteorological structure that caused the rainfall during a 5-year period. A principal component analysis (PCA) was used to determine the origin of major ions (SO₄ ^2?, NO₃ ^?, Cl^?, Ca²⁺, K⁺, Mg²⁺, and Na⁺) in the rainwater. In addition, the meteorological origin of the rain was identified.

Previous works suggested a relationship between acid rain and storm convective clouds. However, statistical analyses of pH values show that only the short-lived con-vective phenomena may cause acid rain in Spain. In fact, rain generated by fronts and that related to long-lived convective systems is neutral or even slightly basic. Results suggest that the acid rain might be related to the meteorological time scale instead of to the cloud type.     

Which meteorological conditions produce worst-case odors from area sources?

Two competing meteorological factors influence atmospheric concentrations of pollutants from open liquid area sources such as wastewater treatment plant units: temperature and stability. High temperatures in summer produce greater emissions from liquid area sources because of increased compound volatility; however, these emissions tend to disperse more readily because of frequent occurrence of unstable conditions. An opposite scenario occurs in winter, with lesser emissions due to lower temperatures, but also frequently less dispersion, due to stable atmospheric conditions. The primary objective of this modeling study was thus to determine whether higher atmospheric concentrations from open liquid area sources occur more frequently in summer, when emissions are greater but so is dispersion, or in winter, when emissions are lesser but so is dispersion. The study utilized a rectangular clarifier emitting hydrogen sulfide as a sample open liquid area source. Dispersion modeling runs were conducted using ISCST3 and AERMOD, encompassing 5 yr of hourly meteorological data divided by season. Emission rates were varied hourly on the basis of a curve-fit developed from previously collected field data. Model output for each season was used to determine (1) maximum 2-min average concentrations, (2) the number of odor events (2-min average concentrations greater than odor detection thresholds), and (3) areas of impact. On the basis of these 3 types of output, it was found that the worst-case odors were associated with summer, considering impacts of meteorology upon both emissions and dispersion. Not accounting for the impact of meteorology on emissions (using a constant worst-case emission rate) caused concentrations to be overpredicted compared with a variable emission rate case. The highest concentrations occurred during stability classes D, E, and F, as anticipated. A comparison of ISCST3 and AERMOD found that for the area source modeled, ISCST3 predicted higher concentrations and more odor events for all seasons.     

PM10 pollution episodes as a function of synoptic climatology in a mountainous industrial area

In this study an attempt is made to investigate the prevailing meteorological conditions during days with high concentrations of PM10 (particles with diameter < 10 microns), collected in the Eordea mountain basin. This is an industrial area in the northwestern mountainous region of Greece. Over the 4-year data-gathering period, the days in which the United States Environmental Protection Agency 24-h PM10 standard was exceeded (episode days), were identified in relation to prevailing synoptic scale and local meteorological conditions. The results indicated that days with increased PM10 concentrations in this area can be grouped into four categories in relation to their synoptic circulation characteristics. The highest concentrations were found to be associated with stagnant conditions. Under these conditions, local circulations developed in the area, resulting in recirculation and accumulation of pollutants.     

A trajectory plume model for simulating air pollution transients

An air quality simulation model that is simple, yet capable of accurately estimating concentrations under unsteady meteorological conditions, has been developed. This trajectory plume model uses the Gaussian plume equation, but has an applicability that is approximately as wide as the Lagrangian puff model. The plume axis is represented by a series of straight-line plume segments. The performance of this model was evaluated by comparing it with other diffusion models. A comparison between simulation results using the present model and those using integrated puff and Eulerian diffusion models for three different metropolitan areas (one in Japan and two in the U.S.) has indicated that a simple trajectory plume model performs as well as the two other more complex models in simulating pollutant dispersion under complicated meteorological conditions such as those which occur during the transition period from a sea breeze to a land breeze.     

Short-range atmospheric dispersion over a heterogeneous surface—I. Lateral dispersion

Results are presented from a series of diffusion trials in which a tracer gas, sulphur hexafluoride, was released from an elevated point source over the heterogeneous surface of the Canadian Precambrian Shield. The experimental procedures used in the sampling and analysis of the tracer gas, and in the collection of supporting meteorological information, are described briefly. Physical and meteorological data are presented for 39 successful trials.Under steady-state meteorological conditions, the crosswind concentration distributions were approximately normal in shape. Lateral Gaussian dispersion parameters were extracted from the profiles and compared statistically with the predictions of a number of standard schemes. Best agreement was found with Pasquill's (1976) method, which uses observed wind direction fluctuations to deduce the lateral spread of the plume. The success of Pasquill's method for the rough, heterogeneous surface of the Shield suggests that it may be quite generally applicable. The spread of the plume was found to scale best with meteorological measurements made near the release height, where the flow is characteristic of the heterogeneous surface as a whole. When scaled using Pasquill's procedure, lateral spread is independent of the type of vegetative cover beneath the plume. Similarly, normalized dispersion over a snow-covered surface progresses at the same rate as over a snow-free surface     

Horizontal inhomogeneities in the particulate carbon component of the Arctic haze

We present results obtained during the ‘AGASP 1983’ Arctic haze aircraft sampling experiment. During this program we operated the aethalometer, an instrument that responds to the aerosol graphitic (‘black’) carbon concentration in real time. Previous results showed strong vertical layering of this component of the Arctic haze. In this paper we present for the first time evidence of horizontal variations of aerosol black carbon concentration. Some of these variations correlate with meteorological parameters, but we also observed horizontal inhomogeneities with a characteristic scale of 50–100 km occurring in the absence of meteorological activity.     

Validation of the lagrangian particle dispersion model FLEXPART against large-scale tracer experiment data

A comprehensive validation of FLEXPART, a recently developed Lagrangian particle dispersion model based on meteorological data from the European Centre for Medium-Range Weather Forecasts, is described in this paper. Measurement data from three large-scale tracer experiments, the Cross-Appalachian Tracer Experiment (CAPTEX), the Across North America Tracer Experiment (ANATEX) and the European Tracer Experiment (ETEX) are used for this purpose. The evaluation is based entirely on comparisons of model results and measurements paired in space and time. It is found that some of the statistical parameters often used for model validation are extremely sensitive to small measurement errors and should not be used in future studies. 40 cases of tracer dispersion are studied, allowing a validation of the model performance under a variety of different meteorological conditions. The model usually performs very well under undisturbed meteorological conditions, but it is less skilful in the presence of fronts. The two ETEX cases reveal the full range of the model’s skill, with the first one being among the best cases studied, and the second one being, by far, the worst. The model performance in terms of the statistical parameters used stays rather constant with time over the periods (up to 117 h) studied here. It is shown that the method used to estimate the concentrations at the receptor locations has a significant effect on the evaluation results. The vertical wind component sometimes has a large influence on the model results, but on the average only a slight improvement over simulations which neglect the vertical wind can be demonstrated. Subgrid variability of mixing heights is important and must be accounted for.     

A size-segregated particle dry deposition scheme for an atmospheric aerosol module

A parameterization of particle dry deposition has been developed for the Canadian Aerosol Module (CAM).This parameterization calculates particle dry deposition velocities as a function of particle size and density as well as relevant meteorological variables. It includes deposition processes, such as, turbulent transfer, Brownian diffusion, impaction, interception, gravitational settling and particle rebound. Particle growth under humid conditions is also considered. Sensitivity tests show that the parameterization provides deposition velocities comparable with recent field observations, especially for sub-micron particles. The present parameterization has also been evaluated using two empirical bulk resistance models, which were originally developed from field observations. The present parameterization has been implemented in CAM, with meteorological input provided by the Canadian Regional Climate Model (RCM) to the eastern North America. A comparison of the modelled dry deposition velocities to a variety of recent measurements that have been reported in the literature demonstrated that the current parameterization produces reasonable results. The main improvement of the current parameterization compared to earlier size-dependent particle dry deposition models is that the current one produces more realistic deposition velocities for sub-micron particles and agrees better with recently published field measurements.     

A New Method for Determining the Contribution of a Refinery to Local SO2 Levels in an Industrial Region

A new method was developed for determining the contribution of one pollutant source to the air quality in an industrialized region. Although the method is general, it is presented in reference to a 130,000 bbl/day petroleum refinery and its effect on ambient SO₂ concentrations in Sarnia, Ontario. The plumes from SO₂ emitters located upwind of the refinery were represented by a single hypothetical plume which influences monitoring stations located upwind as well as downwind from the refinery. However, the refinery emissions affect only the downwind stations. A simple equation was derived by means of which the concentration at the downwind station could be calculated from the concentration at the upwind station and the refinery emission. This equation contains two coefficients A and B which were evaluated such that the difference between the cumulative frequency distributions of the measured and calculated SO₂ concentrations at the downwind station was minimized. For the meteorological conditions and monitoring stations considered, it was found that the refinery contributed less than 4.5 pphm to ambient SO₂ concentrations over 1 hr periods. This result and the validity of the method are discussed.     

OTC－1型开顶式气室的结构和性能

本文详细论述了开放式气室的结构与性能，二氧化碳浓度数据采集系统、物理性能等。并重点介绍了作者自行研制的ＯＴＣ－Ｉ型开顶式气室。     

Modeling transport and deposition of contaminants to ecosystems of concern: a case study for the Laurentian Great Lakes

Transfer efficiency (TE) is introduced as a model output that can be used to characterize the relative ability of chemicals to be transported in the environment and deposited to specific target ecosystems. We illustrate this concept by applying the Berkeley-Trent North American contaminant fate model (BETR North America) to identify organic chemicals with properties that result in efficient atmospheric transport and deposition to the Laurentian Great Lakes. By systematically applying the model to hypothetical organic chemicals that span a wide range of environmental partitioning properties, we identify combinations of properties that favor efficient transport and deposition to the Lakes. Five classes of chemicals are identified based on dominant transport and deposition pathways, and specific examples of chemicals in each class are identified and discussed. The role of vegetation in scavenging chemicals from the atmosphere is assessed, and found to have a negligible influence on transfer efficiency to the Great Lakes. Results indicate chemicals with octanol-water (K(ow)) and air-water (K(aw)) partition coefficients in the range of 10(5)-10(7) and 10(-4)-10(-1) combine efficient transport and deposition to the Great Lakes with potential for biaccumulation in the aquatic food web once they are deposited. A method of estimating the time scale for atmospheric transport and deposition process is suggested, and the effects of degrading reactions in the atmosphere and meteorological conditions on transport efficiency of different classes of chemicals are discussed. In total, this approach provides a method of identifying chemicals that are subject to long-range transport and deposition to specific target ecosystems as a result of their partitioning and persistence characteristics. Supported by an appropriate contaminant fate model, the approach can be applied to any target ecosystem of concern.     

controlled open burning in the san francisco bay area

Intermingled land usage in the 3900 square mile Bay Area Air Pollution Control District presented special problems in curtailing open burning. Regulation 1, adopted in 1957, prohibited most types of open burning, with exceptions for public safety, instruction in fire fighting, flood control, agricultural burning and one- and two-family dwellings.Variances for open burning could be granted by the District’s Hearing Board.The need was established for utilizing the services of professional meteorologists for planning and carrying out open burns.Their proposals to limit adverse effects were : (1) Select a day of no inversion, with wind direction to carry pollutants away from local targets; and, (2) a day of low velocity at ground level, high velocity at high altitudes. Predicted meteorological conditions have been met for up to eight hours in a high percentage of cases. Experience has proven the need for proper stacking and drying of the wood waste to assure high temperature burning, and completion of the burn as scheduled. Even though the cost of hauling to landfills may be substantially more than the cost of burning under a variance, hauling is often selected because of the time required for stacking, drying, and waiting for designated meteorological conditions. Substantial progress has been made in curtailing agricultural burning. Burning of greenhouse waste has been stopped.on emissions from orchard heaters has resulted in replacement with new smokeless heaters.Orchard brush can be burned only on “burn days” designated in the winter when the inversion is predicted to be above 2500 ft. Stubble burning has continued due to the lack of a feasible alternative. Range brush burning also continues, mostly in remote areas of high elevation. Lumbering slash is burned at the insistence of forestry officials. The above burning could be limited to designated burn days, as is successfully being applied to orchard brush. Research on alternatives to agricultural burning is being spearheaded by the University of California, and its agricultural extension service. Each project usually requires several years to carry out and evaluate. Closer cooperation by all involved in agriculture and air pollution control is necessary to develop feasible alternatives to open burning.     

Correlating emissions with time and temperature to predict worst-case emissions from open liquid area sources

The two primary factors influencing ambient air pollutant concentrations are emission rate and dispersion rate. Gaussian dispersion modeling studies for odors, and often other air pollutants, vary dispersion rates using hourly meteorological data. However, emission rates are typically held constant, based on one measured value. Using constant emission rates can be especially inaccurate for open liquid area sources, like wastewater treatment plant units, which have greater emissions during warmer weather, when volatilization and biological activity increase. If emission rates for a wastewater odor study are measured on a cooler day and input directly into a dispersion model as constant values, odor impact will likely be underestimated. Unfortunately, because of project schedules, not all emissions sampling from open liquid area sources can be conducted under worst-case summertime conditions. To address this problem, this paper presents a method of varying emission rates based on temperature and time of the day to predict worst-case emissions. Emissions are varied as a linear function of temperature, according to Henry's law, and a tenth order polynomial function of time. Equation coefficients are developed for a specific area source using concentration and temperature measurements, captured over a multiday period using a data-logging monitor. As a test case, time/temperature concentration correlation coefficients were estimated from field measurements of hydrogen sulfide (H2S) at the Rowlett Creek Wastewater Treatment Plant in Garland, TX. The correlations were then used to scale a flux chamber emission rate measurement according to hourly readings of time and temperature, to create an hourly emission rate file for input to the dispersion model ISCST3. ISCST3 was then used to predict hourly atmospheric concentrations of H2S. With emission rates varying hourly, ISCST3 predicted 384 acres of odor impact, compared with 103 acres for constant emissions. Because field sampling had been conducted on relatively cool days (85-90 degrees F), the constant emission rate underestimated odor impact significantly (by 73%).