Air quality modeling in the South Coast Air Basin of California: what do the numbers really mean?

This study evaluates air quality model sensitivity to input and to model components. Simulations are performed using the California Institute of Technology (CIT) airshed model. Results show the impacts on ozone (O3) concentration in the South Coast Air Basin (SCAB) of California because of changes in: (1) input data, including meteorological conditions (temperature, UV radiation, mixing height, and wind speed), boundary conditions, and initial conditions (ICs); and (2) model components, including advection solver and chemical mechanism. O3 concentrations are strongly affected by meteorological conditions and, in particular, by temperature. ICs also affect O3 concentrations, especially in the first 2 days of simulation. On the other hand, boundary conditions do not significantly affect the absolute peak O3 concentration, although they do affect concentrations near the inflow boundaries. Moreover, predicted O3 concentrations are impacted considerably by the chemical mechanism. In addition, dispersion of pollutants is affected by the advection routine used to calculate its transport. Comparison among CIT, California Photochemical Grid Model (CALGRID), and Urban Airshed Model air quality models suggests that differences in O3 predictions are mainly caused by the different chemical mechanisms used. Additionally, advection solvers contribute to the differences observed among model predictions. Uncertainty in predicted peak O3 concentration suggests that air quality evaluation should not be based solely on this single value but also on trends predicted by air quality models using a number of chemical mechanisms and with an advection solver that is mass conservative.     

Air Quality Modeling in the South Coast Air Basin of California: What Do the Numbers Really Mean?

Abstract

This study evaluates air quality model sensitivity to input and to model components. Simulations are performed using the California Institute of Technology (CIT) airshed model. Results show the impacts on ozone (O₃) concentration in the South Coast Air Basin (SCAB) of California because of changes in: (1) input data, including meteorological conditions (temperature, UV radiation, mixing height, and wind speed), boundary conditions, and initial conditions (ICs); and (2) model components, including advection solver and chemical mechanism. O₃ concentrations are strongly affected by meteorological conditions and, in particular, by temperature. ICs also affect O₃ concentrations, especially in the first 2 days of simulation. On the other hand, boundary conditions do not significantly affect the absolute peak O₃ concentration, although they do affect concentrations near the inflow boundaries. Moreover, predicted O₃ concentrations are impacted considerably by the chemical mechanism. In addition, dispersion of pollutants is affected by the advection routine used to calculate its transport. Comparison among CIT, California Photochemical Grid Model (CALGRID), and Urban Airshed Model air quality models suggests that differences in O₃ predictions are mainly caused by the different chemical mechanisms used. Additionally, advection solvers contribute to the differences observed among model predictions. Uncertainty in predicted peak O₃ concentration suggests that air quality evaluation should not be based solely on this single value but also on trends predicted by air quality models using a number of chemical mechanisms and with an advection solver that is mass conservative.     

Aerosol characters from the desert region of Northwest China and the Yellow Sea in spring and summer: observations at Minqin,Qingdao, and Qianliyan in 1995–1996

Aerosol samples were collected from Northwest China desert region (Minqin), coastal suburb (Qingdao) and interior of the Yellow Sea (Qianliyan) in spring and summer of 1995 and 1996. Samples were analysed for major components, carbon and sulphur. The results show that concentrations of aerosols change considerably in time and space. The crustal materials carried by cold front system increase notably the aerosol concentration (mass/unit vol.) over the Yellow Sea but reduce the percentage contribution of pollutants and sea-salt. The sea-salt and regional aerosols become dominant fractions in coastal atmosphere in summer when the dust storms are expired in source region and the Southeast monsoon starts in the Pacific Ocean.     

Characterization of PM25 and PM10 in the South Coast Air Basin of Southern California: Part 1—Spatial Variations

ABSTRACT

In December 1994, the South Coast Air Quality Management District (SCAQMD) initiated a comprehensive program, the PM₁₀ Technical Enhancement Program (PTEP), to characterize fine PM in the South Coast Air Basin (SCAB). A 1-year special particulate monitoring project was conducted from January 1995 to February 1996 as part of the PTEP. Under this enhanced monitoring, HNO₃, NH₃, and speciated PM₁₀ and PM_2.5 concentrations were measured at five stations (Anaheim, downtown Los Angeles, Diamond Bar, Fontana, and Rubidoux) in the SCAB and at one background station at San Nicolas Island. PM_2.5 and PM₁₀ mass and 43 individual species were analyzed for a full chemical speciation of the particle data. The PTEP data indicate that the most abundant chemical components of PM₁₀ and PM₂₅ in the SCAB are NH₄+ (8-9% of PM₁₀ and 14-17% of PM₂₅), NO₃ ^- (23-26% of PM₁₀ and 28-41% of PM₂₅), SO₄= (6-11% of PM₁₀ and 9-18% of PM_{2 5}), organic carbon (OC) (15-19% of PM₁₀ and 18-26% of PM_2.5), and elemental carbon (EC) (5-8% of PM₁₀ and 8-13% of PM₂₅). On an annual average basis, PM₂₅ comprises 52-59% of the SCAB PM₁₀. Annual average PM₁₀ and PM_2.5 concentrations showed strong spatial variations, low at coastal sites and high at inland sites. Annual average PM₁₀ concentrations varied from 40.8 ug/m³ at Anaheim to 76.8 ug/m³ at Rubidoux, while annual average PM_2.5 concentrations varied from 21.7 ug/m³ at Anaheim to 39.8 ug/m³ at Rubidoux. The chemical characterizations of the PM_2.5 and PM₁₀ concentrations, as well as their spatial variations, were examined; the important findings are summarized in this paper, and the temporal variations are discussed in the companion paper.¹     

Characterization of PM25 and PM10 in the South Coast Air Basin of Southern California: Part 2—Temporal Variations

ABSTRACT

The South Coast Air Quality Management District (SCAQMD) conducted a 1-year special particulate monitoring study from January 1995 to February 1996. This monitoring data indicates that high PM₁₀ and PM_{2 5} concentrations were observed in the fall (October, November, and December), with November concentrations being the highest. During the rest of the year, PM_2.5 and PM₁₀ masses gradually increased from January to September. Monthly PM₁₀ mass varied from 20 to 120 |ig/m³, and monthly PM₂₅ mass varied from 13 to 63 |j.g/m³. The PM_2.5-to-PM₁₀ ratio varied daily and ranged between 22 and 96%. Two types of high-PM days were observed. The first type was observed under fall stagnation conditions, which lead to high secondary species concentrations. The second type was observed under high wind conditions, which lead to high primary coarse particles of crustal components. The highest 24-hr average PM₁₀ concentration (226.3 |ig/m³) was observed at the Fontana station, while the highest PM₂₅ concentration (129.3 |ig/m³) was observed at the Diamond Bar station.     

Occurrence,impact, toxicity,and degradation methods of microplastics in environment—a review

Environmental Science and Pollution Research - Microplastic defines as a tiny plastic particle that has a size of less than 5 mm and is ubiquitous in the environment. Due to the tiny size,...     

Spatial variations in the aeolian deposition of dust – the effect of a city: a case study in Be'er-Sheva,Israel

The effect of buildings on the dry deposition of dust particles was investigated in Be'er-Sheva, a desert city with about 140,000 inhabitants in southern Israel, and at two reference points in the surrounding rural area. The mineral and chemical composition of dust sampled at all sites was similar, reflecting the composition of the local loess soil, its likely origin. However, dust deposited in the traps set up in the vicinity of buildings in the city was significantly coarser than the dust which accumulated in similar traps at exposed sites in the countryside. The amount of dust (by weight) in the urban dust traps was on an average more than twice the amount deposited in the rural area. The differences in grain-size distribution and quantity of dust are attributed to the properties of the urban wind field and to various effects of human activity in the city.     

Psychoactive drugs: occurrence in aquatic environment,analytical methods,and ecotoxicity—a review

This review focused on seven psychoactive drugs being six benzodiazepines (alprazolam, bromazepam, clonazepam, diazepam, lorazepam, and oxazepam) and one antidepressant (citalopram) widely consumed by modern society and detected in different aqueous matrices (drinking water, surface water, groundwater, seawater, estuary water, influent and effluent of wastewater treatment plants). The review included 219 selected scientific papers from which 1642 data/entries were obtained, each entry corresponding to one target compound in one aqueous matrix. Concentrations of all investigated drugs in all aqueous matrices varied from 0.14 to 840,000 ng L^?1. Citalopram presented the highest concentrations in the aqueous matrices. Based on the Wilcoxon-Mann-Whitney test, differences between wastewater influents and effluents were not significant for most wastewater categories, suggesting that conventional wastewater treatment systems as such do not remove or remove partially these compounds. High-income countries showed much lower concentrations in surface water than the group formed by upper-middle-, lower-middle-, and low-income countries. Regarding analytical methods, solid-phase extraction (SPE) was by far the most used extraction method (83%) and performance liquid chromatography (HPLC) (73%) coupled to mass spectrometry (99%) the most common analytical method. Changes in behavior and in survival rates were the most common effects reported on bioindicators (aquatic species) due to the presence of these drugs in water. Concentrations of psychoactive drugs found in surface waters were most of the time within the range that caused measurable toxic effects in ecotoxicity assays.     

SimPhy: a simulation game to lessen the impact of phytosanitaries on health and the environment—the case of Merja Zerga in Morocco

Diffuse phytosanitary pollution is a complex phenomenon to manage. Reducing this type of pollution is one of today’s key socio-economic and environmental challenges. At the regional level, few approaches enable the actors concerned to implement agricultural management strategies to reduce the use and impact of phytosanitary products. Our research problem focused on the consequences of intensive agriculture and, in particular, how to evaluate the impact of phytosanitary products on human health and the environment. In this article, we present the SimPhy simulation game which places the actors from a given region directly into a situation in which they manage farms whilst under pressure to reduce phytosanitaries (quantity and toxicity). The application focused on the Merja Zerga catchment area in Morocco. The region is dominated by intensive agriculture which is located upstream from a Ramsar-classified wetland area. The SimPhy simulation game is based on a decision support system-type tool. It allows us to anticipate the impact of regulations on farming systems. It also enables us to analyse the consequences of the actors’ strategies on farm economies, human health and the quality of ecosystems. Initial results from the SimPhy simulation game enabled the technicians from Agricultural Development Center (CDA) themselves to learn about managing agricultural production systems in a dynamic and interactive fashion. With the simulation game, it was possible to learn about the farmer's ability to adapt to new regulatory constraints, and the involved consequences for toxicity risks for human health and the environment.     

Measurements of ammonia concentrations,fluxes and dry deposition velocities to a spruce forest 1991–1995

The dry deposition velocities and fluxes of ammonia have been estimated from measurements of the vertical gradient of ammonia and micrometeorology above a spruce forest in western Jutland, Denmark. Measurements have been made in seven periods, each lasting about one week and covering all seasons and different meteorological situations. Different deposition characteristics were observed, depending on the ammonia concentration and the relative humidity. At conditions with westerly winds, the wind brings air masses from the North Sea with low concentration levels of ammonia to the site, while at conditions with easterly winds, the air have passed central Jutland with large emission areas. Some of the relatively low deposition velocities or emissions were observed during conditions with low ammonia concentration and westerly winds. These observations might relate to a compensation point of the forest, i.e. an ammonia concentration below which the trees and/or the surface emit ammonia due to an equilibrium with the ammonia inside the needles or on the surface. Emission of ammonia was also observed at relatively high ammonia concentration levels (above 2 μg NH₃–N m^-3), mainly during one measuring period characterized by easterly winds with dry conditions and high ammonia concentrations, and the emissions might relate to evaporation from ammonia saturated surfaces or emission from mineralization in the forest soil. In general, relatively high net deposition velocities were observed during conditions with relative humidity above 80% or at ammonia concentrations moderate higher than a given (temperature dependent) compensation point. During stable conditions some observations revealed that the gradient above the canopy not necessarily represents the exchange with the canopy.     

Distribution,persistence, and fate of mexacarbate in the aquatic environment of a mixed‐wood boreal forest

Abstract

The distribution and persistence of aerially applied mexacarbate were studied in a New Brunswick aquatic forest environment after spraying twice at a dosage of 70 g A.l./ha using a fixed‐wing aircraft. Average droplet density (drops/cm²) and ground deposition (g A.1./ha) between the two applications differed considerably. The values for the first and second applications were 1.7 and 0.73, and 5.2 and 2.0, respectively; but the average NMD (20 μm) and VMD (36 μm) for both applications were nearly the same. The maximum 1‐h postspray concentrations of mexacarbate in the stream and pond waters were 0.73 and 18.74 ppb, respectively. Concentrations fell rapidly to below detection limits within 12 h in stream and within 3 d in pond water. Cattails (Typha latifolia), manna grass (Glyceria borealis) and bog moss (Sphagnum sp.) collected from the pond contained peak 1‐h postspray concentrations of 720, 482 and 81 ppb, respectively. The concentration levels decreased rapidly and the average half‐lives of the chemical in them were about 3.9, 8.5 and 2.0 h. Bog moss, stream moss (Fontinalis sp.), watercress (Nasturtium officinalis), buttercup (Ranunculus aquatilis) and green alga (Drapamaldia sp.) sampled from the stream sites did not contain measurable levels of mexacarbate. Also, caged and wild tadpoles (Rana clamitans melanota) from the pond, and brook trout (Salvelinus fontinalis) (caged and wild), Atlantic salmon (Salmo salar) (wild) and mayfly nymphs (Ephemeralla sp.) collected from the stream did not contain any of the material. Mexacarbate was not detected in stream and pond sediments. The demethylated products, 4‐methylamino and 4‐amino‐3,5‐xylyl methylcarbamates and the phenol, 4‐dimethylamino‐3,5‐xylenol, were frequently detected as metabolites in water and in the aquatic plants. The presence of these compounds showed that demethylation and hydrolytic routes are the major metabolic pathways for the dissipation of mexacarbate from these substrates.     

Evolution of the Magnitude and Spatial Extent of the Weekend Ozone Effect in California’s South Coast Air Basin, 1981–2000

Abstract

Since the mid-1970s, ozone (O₃) levels in portions of California’s South Coast Air Basin (SoCAB) on weekends have been as high as or higher than levels on weekdays, even though emissions of O₃ precursors are lower on weekends. Analysis of the ambient data indicates that the intensity and spatial extent of the weekend O₃ effect are correlated with day-of-week variations in the extent of O₃ inhibition caused by titration with nitric oxide (NO), reaction of hydroxyl radical (OH) with nitrogen dioxide (NO₂), and rates of O₃ accumulation. Lower NO mixing ratios and higher NO₂/oxides of nitrogen (NO_x) ratios on weekend mornings allow O₃ to begin accumulating approximately an hour earlier on weekends. The weekday/weekend differences in the duration of O₃ accumulation remained relatively constant from 1981 to 2000. In contrast, the rate of O₃ accumulation decreased by one-third to one-half over the same period; the largest reductions occurred in the central basin on weekdays. Trends in mixing ratios of O₃ precursors show a transition to lower volatile organic compound (VOC)/NO_x ratios caused by greater reductions in VOC emissions. Reductions in VOC/NO_x ratios were greater on weekdays, resulting in higher VOC/NO_x ratios on weekends relative to weekdays. Trends in VOC/NO_x ratios parallel the downward trend in peak O₃ levels, a shift in the location of peak O₃ from the central to the eastern portion of the basin, and an increase in the magnitude and spatial extent of the weekend O₃ effect.     

Atmospheric dispersion and transport within coastal regions—Part II. Tracer study of industrial emissions in the California Delta Region

Eight large-scale atmospheric tracer tests, utilizing CBrF₃ and/or SF₆, were conducted during September, 1976, within the California Delta Region. The purpose of this study was to demonstrate the large-scale application of single and double tracer techniques to the study of pollutant transport and dispersion under complex, coastal meteorological conditions.The resulting tracer data base was comprehensive enough to permit accurate mass balances of the tracer; essentially all of the tracer was accounted for by this analysis. On the average, plumes emitted from the Montezuma Hills during the test periods were transported southeast over Stockton into the San Joaquin Valley. As a result of the steady nature of the winds, the commonly used Hino correction was found to grossly underestimate the hourly averaged tracer concentrations computed from 10-s averaged concentrations.Experimentally determined rates of dispersion were greater than those associated with Pasquill-Gifford dispersion curves. In spite of the complex meteorology and terrain, estimates of tracer concentrations based upon the Gaussian plume model were found to be reasonably accurate.The relationship between the horizontal standard deviation of the wind, σ_θ, and the horizontal dispersion parameter of the plume, σ_y, was found to follow σ_y∼-0.85 xσ_θ, where x is the downwind distance of the plume center. Calculated trajectories and arrival times of air parcels based upon a numerical solution to the two-dimensional mass balance equation were found to be in excellent agreement with the tracer data.     

Diurnal and Weekday Variations in the Source Contributions of Ozone Precursors in California’s South Coast Air Basin

Abstract

For at least 30 years, ozone (O₃) levels on weekends in parts of California’s South Coast (Los Angeles) Air Basin (SoCAB) have been as high as or higher than on weekdays, even though ambient levels of O₃ precursors are lower on weekends than on weekdays. A field study was conducted in the Los Angeles area during fall 2000 to test whether proposed relationships between emission sources and ambient nonmethane hydrocarbon (NMHC) and oxides of nitrogen (NO_x) levels can account for observed diurnal and day-of-week variations in the concentration and proportions of precursor pollutants that may affect the efficiency and rate of O₃ formation. The contributions to ambient NMHC by motor vehicle exhaust and evaporative emissions, estimated using chemical mass balance (CMB) receptor modeling, ranged from 65 to 85% with minimal day-of-week variation. Ratios of ambient NO_x associated with black carbon (BC) to NO_x associated with carbon monoxide (CO) were approximately 1.25 ± 0.22 during weekdays and 0.76 ± 0.07 and 0.52 ± 0.07 on Saturday and Sunday, respectively. These results demonstrate that lower NO_x emissions from diesel exhaust can be a major factor causing lower NO_x mixing ratios and higher NMHC/NO_x ratios on weekends. Nonmobile sources showed no significant day-of-week variations in their contributions to NMHC. Greater amounts of gasoline emissions are carried over on Friday and Saturday evenings but are, at most, a minor factor contributing to higher NMHC/NO_x ratios on weekend mornings.     

The use of vegetation,bees, and snails as important tools for the biomonitoring of atmospheric pollution—a review

The continuous discharge of diverse chemical products in the environment is nowadays of great concern to the whole world as some of them persist in the environment leading to serious diseases. Several sampling techniques have been used for the characterization of this chemical pollution, although biomonitoring using natural samplers has recently become the technique of choice in this field due to its efficiency, specificity, and low cost. In fact, several living organisms known as biomonitors could accumulate the well-known persistent environmental pollutants allowing their monitoring in the environment. In this work, a review on environmental biomonitoring is presented. The main sampling techniques used for monitoring environmental pollutants are first reported, followed by an overview on well-known natural species used as passive samplers and known as biomonitors. These species include conifer needles, lichen, mosses, bees and their byproducts, and snails, and were widely used in recent research as reliable monitors for environmental pollution.

     

Poland’s environment - past,present and future state of the environment in the vistula and odra river basins

In the middle of the last century in the case of many river basins, it became obvious that the targets of the Helsinki-Commission (HELCOM) concerning a 50% reduction of nitrogen and phosphorus inputs to the Baltic Sea had not been reached. Such conclusions could be derived from the observed loads. But the measurements regarding the analysis were not sufficient to determine what the reasons for this report were, what has to be done to fulfil this agreement and to evaluate the time at which the targets can be reached. This contribution presents the current state of Polish surface water quality as well as results of modelling nutrient and heavy metal emissions into the two biggest Polish river basins: Vistula and Odra, which both cover approximately 90% of Poland's territory.     

Modelling base cations in Europe—sources,transport and deposition of calcium

The deposition of the base cations calcium, magnesium and potassium from the atmosphere needs to be quantified in the calculation of the total deposited acidity in the critical loads approach. Of these base cations, calcium has been found to be the most important in terms of mass deposited. However, the sources of calcium to the atmosphere are not well understood. Recently, the first spatially disaggregated inventory of industrial calcium emissions for Europe was presented by Lee and Pacyna (1998) who estimated a total European emission of 0.7–0.8 Mt yr^-1. However, it is thought that wind blown dust from soils contributes a substantial fraction to the deposition of calcium. In this work, the source strength of calcium from arid regions within the EMEP modelling domain was estimated using the global mineral dust emission data base of Tegen and Fung (1994) and an estimation of the calcium content of soils. This results in a “natural” calcium emission of 6 Mt yr^-1. A long-range transport model, TRACK, was used to calculate the wet and dry deposition of calcium arising from these industrial and natural sources to the UK which resulted in a total deposition of 29–30 kt yr^-1. Of this annual deposition, 0.6–0.7 kt arises from cement manufacturing, 0.02–0.03 kt from iron and steel manufacturing, 0.8–0.83 kt from a large point source power generation, and 28 kt from power generation from a small boiler plant. The natural emissions of calcium from arid regions result in a deposition of calcium to the UK of 0.5 kt yr^-1. The measured wet deposition of calcium to the UK is 89 kt yr^-1 and the estimated dry deposition 14 kt yr^-1. The short-fall in the modelled deposition of calcium is thus of the order of 70 kt yr^-1, which is suggested to arise from wind-blown dust from agricultural land in the UK and mainland Europe. The estimated emissions, and thus modelled deposition are rather uncertain, such that estimating deposition of calcium attributable to agricultural soil emissions by differencing has a large uncertainty. However, this is the first such study of its kind for Europe and represents a first step towards understanding the sources of calcium and their contribution to mitigating deposited acidity from acidifying pollutants such as sulphur dioxide, nitrogen oxides and ammonia.