Behaviour and variability of local and regional oxidant levels (OX = O3 + NO2) measured in a polluted area in central-southern of Iberian Peninsula

The purpose of this work is to contribute to the understanding of the photochemical air pollution in central-southern of the Iberian Peninsula, analysing the behaviour and variability of oxidant levels (OX?=?O₃?+?NO₂), measured in a polluted area with the highest concentration of heavy industry in central Spain. A detailed air pollution database was observed from two monitoring stations. The data period used was 2008 and 2009, around 210,000 data, selected for its pollution and meteorological statistics, which are very representative of the region. Data were collected every 15 min, however hourly values were used to analyse the seasonal and daily ozone, NO, NO₂ and OX cycles. The variation of OX concentrations with NO _x is investigated, for the first time, in the centre of the Iberian Peninsula. The concentration of OX was calculated using the sum of a NO _x -independent ‘regional’ contribution (i.e. the O₃ background), and a linearly NO _x -dependent ‘local’ contribution. Monthly dependence of regional and local OX concentration was observed to determine when the maximum values may be expected. The variation of OX concentrations with levels of NO _x was also measured, in order to pinpoint the atmospheric sources of OX in the polluted areas. The ratios [NO₂]/[OX] and [NO₂]/[NO _x ] vs. [NO _x ] were analysed to find the fraction of OX in the form of NO₂, and the possible source of the local NO _x -dependent contribution, respectively. The progressive increase of the ratio [NO₂]/[OX] with [NO _x ] observed shows a greater proportion of OX in the form of NO₂ as the level of NO _x increases. The higher measured values in the ratio [NO₂]/[NO _x ] should not be attributed to NO _x emissions by vehicles; they could be explained by industrial emission, termolecular reactions or formaldehyde and HONO directly emitted by vehicles exhausts. We also estimate the rate of NO₂ photolysis, J _NO2?=?0.18–0.64 min^?1, a key atmospheric reaction that influence O₃ production and then the regional air quality. The first surface plot study of annual variation of the daily mean oxidant levels, obtained for this polluted area may be used to improve the atmospheric photochemical dynamic in this region of the Iberian Peninsula where there are undeniable air quality problems.     

Ground level ozone concentrations and its association with NOx and meteorological parameters in Kathmandu valley, Nepal

This paper summarizes the results of a yearlong continuous measurements of gaseous pollutants, NO, NO₂, NO_x and O₃ in the ambient air at Kathmandu valley. Measured concentration of the pollutants in study area is a function of time. NO, NO₂ and O₃ peak occurred in succession in presence of sunlight. At the time of maximum O₃ concentration most of the NO_x are utilized. The diurnal cycle of ground level ozone concentrations, revealed mid-day peak with lower nocturnal concentrations and inverse relationship exists between O₃ and NO_x, which are evidences of photochemical O₃ formation. The observed ground level ozone during monsoon is slight lower than the pre-monsoon value. Further, lack of rainfall and higher temperature, solar radiation in the pre-monsoon have given rise to the gradual build up of ozone and it is lowest during winter. Ground level ozone concentrations measured during bandha (general strike) and weekend are 19% and 13% higher than those measured during weekdays. The most effective ozone abatement strategy for Kathmandu Valley may be control of NO_x emissions.     

Air Quality Modeling of Interpollutant Trading for Ozone Precursors in an Urban Area

Abstract

Emission trading is a market‐based approach designed to improve the efficiency and economic viability of emission control programs; emission trading has typically been confined to trades among single pollutants. Interpollutant trading (IPT), as described in this work, allows for trades among emissions of different compounds that affect the same air quality end point, in this work, ambient ozone (O₃) concentrations. Because emissions of different compounds impact air quality end points differently, weighting factors or trading ratios (tons of emissions of nitrogen oxides (NO_x) equivalent to a ton of emissions of volatile organic compounds [VOCs]) must be developed to allow for IPT. In this work, IPT indices based on reductions in O₃ concentrations and based on reductions in population exposures to O₃ were developed and evaluated using a three‐dimensional gridded photochemical model for Austin, TX, a city currently on the cusp of nonattainment with the National Ambient Air Quality Standards for O₃ concentrations averaged over 8 hr. Emissions of VOC and NO_x from area and mobile sources in Austin are larger than emissions from point sources. The analysis indicated that mobile and area sources exhibited similar impacts. Trading ratios based on maximum O₃ concentration or population exposure were similar. In contrast, the trading ratios did exhibit significant (more than a factor of two) day‐to‐day variability. Analysis of the air quality modeling indicated that the daily variability in trading ratios could be attributed to daily variations in both emissions and meteorology.     

Assessment of the Ozone-Nitrogen Oxide-Volatile Organic Compound Sensitivity of Mexico City through an Indicator-Based Approach: Measurements and Numerical Simulations Comparison

Abstract

The ozone (O₃) sensitivity to nitrogen oxides (NO_x, or nitric oxide [NO] + nitrogen dioxide [NO₂]) versus volatile organic compounds (VOCs) in the Mexico City metropolitan area (MCMA) is a current issue of scientific controversy. To shed light on this issue, we compared measurements of the indicator species O₃/NO_y (where NO_y represents the sum of NO + NO₂ + nitric acid [HNO₃] + peroxyacetyl nitrate [PAN] + others), NO_y, and the semiempirically derived O₃/NO_{z surrogate} (where NO_{z surrogate} is the derived surrogate NO_z, and NO_z represents NO_x reaction products, or NO_y – NO_x) with results of numerical predictions reproducing the transition regimes between NO_x and VOC sensitivities. Ambient air concentrations of O₃, NO_x, and NO_y were measured from April 14 to 25, 2004 in one downwind receptor site of photo-chemically aged air masses within Mexico City. MCMA-derived transition values for an episode day occurring during the same monitoring period were obtained through a series of photochemical simulations using the Multiscale Climate and Chemistry Model (MCCM). The comparison between the measured indicator species and the simulated spatial distribution of the indicators O₃/NO_y, O₃/NO_{z surrogate}, and NO_y in MCMA suggest that O₃ in this megacity is likely VOC-sensitive. This is in opposition to past studies that, on the basis of the observed morning VOC/NO_x ratios, have concluded that O₃ in Mexico City is NO_x-sensitive. Simulated MCMA-derived sensitive transition values for O₃/NO_y, hydrogen peroxide (H₂O₂)/HNO₃, and NO_y were found to be in agreement with threshold criteria proposed for other regions in North America and Europe, although the transition crossover for O₃/NO_z and O₃/HNO₃ was not consistent with values reported elsewhere. An additional empirical evaluation of weekend/weekday differences in average maximum O₃ concentrations and 6:00- to 9:00-a.m. NO_x and NO levels registered at the same site in April 2004 indirectly confirmed the above results. A preliminary conclusion is that additional reductions in NO_x emissions in MCMA might cause an increase in presently high O₃ levels.     

Modeling the long-term frequency distribution of regional ozone concentrations

Efficient methods are developed for modeling emissions – air quality relationships that govern ozone and NO₂ concentrations over very long periods of time. A baseline model evaluation study is conducted to assess the accuracy and speed with which the relationship between pollutant emissions and the frequency distribution of O₃ concentrations throughout the year can be computed along with annual average NO₂ values using a deterministic photochemical airshed model driven by automated objective analysis of measured meteorological parameters. Methods developed are illustrated by application to the air quality situation that exists in Southern California. Model performance statistics for O₃ are similar to the results obtained in previous short-term episodic model evaluation studies that were based on hand-crafted meteorological inputs that are supplemented by expensive field measurement campaigns. Model predictions at one of the highest NO₂ concentration sites in the US indicate that measured violation of the US annual average NO₂ air quality standard at that site occurs because other species such as HNO₃ and PAN are measured as if they were NO₂ by the chemiluminescent NO_x monitors in current use.     

Air pollution in cities

Air quality in cities is the result of a complex interaction between natural and anthropogenic environmental conditions. Air pollution in cities is a serious environmental problem – especially in the developing countries. The air pollution path of the urban atmosphere consists of emission and transmission of air pollutants resulting in the ambient air pollution. Each part of the path is influenced by different factors. Emissions from motor traffic are a very important source group throughout the world. During transmission, air pollutants are dispersed, diluted and subjected to photochemical reactions. Ambient air pollution shows temporal and spatial variability. As an example of the temporal variability of urban air pollutants caused by motor traffic, typical average annual, weekly and diurnal cycles of NO, NO₂, O₃ and O_x are presented for an official urban air-quality station in Stuttgart, southern Germany. They are supplemented by weekly and diurnal cycles of selected percentile values of NO, NO₂, and O₃. Time series of these air pollutants give information on their trends. Results are discussed with regard to air pollution conditions in other cities. Possibilities for the assessment of air pollution in cities are shown. In addition, a qualitative overview of the air quality of the world's megacities is given.     

Traffic pollution in a downtown site of Buenos Aires City

It has recently been recognized that air and noise pollution constitutes an extended problem over the densely populated city of Buenos Aires. Traffic emissions are of paramount concern, especially along narrow and main traffic arteries. In spite of these considerations, few systematic studies have been undertaken to evaluate the air quality in the metropolitan area of the city. In 1996, concentrations of carbon monoxide (CO), nitric oxide (NO), nitrogen dioxide (NO₂) and ozone (O₃) were simultaneously measured for the first time using a continuous monitoring station. This station was placed in a building at Belgrano Avenue, which is a heavy traffic street in the downtown area of the city (Bogo et al., Atmospheric Environment 33 (1999) 2587. In this work, we analyze the dependence of the measured primary pollutants, CO and the mixture of nitrogen oxides (NO_x), with meteorological conditions, traffic emissions and monitoring location. We compare the registered values with the results obtained from modeling the dispersion of the pollutants emitted from mobile and area sources. We also discuss the relevance of street canyon effects compared with background concentrations of these pollutants.     

Nonmethane Organic Compound to Nitrogen Oxide Ratios and Organic Composition in Cities and Rural Areas

The observed ranges in nonmethane organic compound (NMOC) concentrations, NMOC composition and nitrogen oxides (NO_X) concentrations have been evaluated for urban and nonurban areas at ground level and aloft of the contiguous United States. The ranges in NMOC to NO_X ratios also are considered. The NMOC composition consistently shifts towards less reactive compounds, especially the alkanes, in air parcels over nonurban areas compared to the NMOC composition near ground level within urban areas. The values for the NMOC to NO_X ratios, 1.2 to 4.2, in air aloft over nonurban areas are lower than in air at ground level urban sites, ≥8, and much lower than in air at ground level nonurban sites, ≥20.

The layers of air aloft over a number of nonurban areas of the United States tend to accumulate NO_X emissions from the tall stacks of large fossil fuel power plants located at nonurban sites. During the night into the morning hours, the air aloft is isolated from any fresh NMOC emissions predominately coming from near surface sources. Conversely, during this extended period of restricted vertical mixing, air near the surface accumulates NMOC emissions while this air is isolated from the major NO_X sources emitting aloft. These differences in the distribution of NMOC and NO_X sources appear to account for the much larger NMOC to NO_X ratios reported near ground level compared to aloft over nonurban areas.

Two types of experimental results are consistent with these conclusions: (1) observed increases in surface rural NO_X concentrations during the morning hours during which the mixing depth increases to reach the altitude at which NO_X from the stacks of fossil fuel power plants is being transported downwind; (2) high correlations of total nitrate at rural locations with Se, which is a tracer for coal-fired power plant NO_X emissions.

The implications of these conclusions from the standpoint of air quality strategies are suggested by use of appropriate scenarios applied to both urban and regional scale photochemical air quality models. The predictions from urban model scenarios with NMOC to NO_X ratios up to 20 are that NO_X control will result in the need for the control of more NMOC emissions than necessary in the absence of NO_X control, in order to meet the O₃ standard. On a regional scale, control of NO_X emissions from fossil fuel power plants has little overall effect regionally but does result on a more local scale in both small decreases and increases in O₃ concentrations compared to the baseline scenario without NO_X control. The regional modeling results obtained to date suggest that NO_X control may be effective in reducing O₃ concentrations only for a very limited set of conditions in rural areas.     

Partitioning, sources and variability of regional and local oxidant (OX = O3 + NO2) in a coastal rural area in the southwest of Iberian Peninsula

The purpose of this work is to investigate the behaviour and variability of oxidant levels (OX?=?NO₂?+?O₃), for the first time, in a rural coastal area in the southwest of the Iberian Peninsula, affected by several air masses types. Detailed database (built-up over the years 2008 to 2011, and containing around 500,000 data) from the Atmospheric Sounding Station “El Arenosillo” was used. The observed daily cycles of NO _x and OX were influenced by air masses coming from industrial and urban area. It can be seen that the concentration of OX is made up of a NO _x -independent ‘regional’ contribution (i.e. the O₃ background), and a linearly NO _x -dependent ‘local’ contribution from primary emissions, such as traffic. The local emission is very low in this area. Also, the regional contribution is similar to unpolluted sites and presents seasonal variation, being higher in May. However, our measurements showed that the proportion of OX in the form of NO₂ increases with the increase in NO _x concentration during the day. The higher proportion of NO₂ observed at night must be due to the conversion of NO to NO₂ by the NO?+?O₃ reaction. With regards to the source of the local NO _x -dependent contribution, it may be attributed to industrial emission, or the termolecular reaction 2NO?+?O₂?=?2NO₂, at high-NO _x levels and stagnant air during several days. Finally, we estimated the photolysis rate of NO₂, J _NO2, an important key atmospheric reaction coupled with ozone. We also present surface plots of annual variation of the daily mean NO _x and OX levels, which indicate that oxidants come from transport processes instead of local emissions associated as local photochemistry.     

On the Relation Between the Indoor and Outdoor Concentrations of Nitrogen Oxides

Simultaneous measurements were made of the concentrations of NO, NO₂, and CO inside and outside of a building. The building is located in the Los Angeles area, which is heavily polluted by photochemical smog, and the experiments were conducted at a time of the year when the pollutants in question tend to be high. The results shows that there is a direct relationship between the inside and outside concentrations, and that the phase lag between the concentrations depends principally on the ratio of the building volume to the ventilation rate. Although the outside concentrations of the pollutants in question did not follow the same pattern every day, peak concentrations seemed to be related to “rush-hour” traffic. By reducing ventilation rates during these periods, it may be possible to reduce the concentration peaks inside of the building. The building involved in the current study was not located in the immediate vicinity of heavy traffic, and the indoor concentrations of NO, NO₂, and CO did not appear to be very severe when compared to those defined by present air quality standards. Finally, the results support the belief that NO and O₃ do not co-exist indoors except in very small quantities.     

Continuous measurement of gaseous pollutants in Buenos Aires city

Data on CO, NO, NO₂ and O₃ concentrations measured in Buenos Aires city using a continuous monitoring station are reported. This is the first systematic study of this kind carried out in the city, which is, together with its surroundings, the third more populated in Latin America. Measurements were performed during 12 months in one of the principal avenues near downtown. Results indicate that vehicular traffic is the principal source of CO and NO_x. The concentration of O₃ is generally quite low and results from the mixing of clean air masses with exhaust gases containing high amounts of NO. The monthly averages of CO and NO decrease from Winter to Summer in correlation with the increase of the mean wind speed and average temperature. These results are compared with previous measurements on the spatial distribution of NO₂ in the whole city using passive diffusion tubes and with the concentration of CO, which is being continuously registered since several years in the downtown area. Measurements performed at a green, windy, low traffic area beneath the La Plata river are also shown.     

Sensitivity of ozone concentrations to diurnal variations of surface emissions in Mexico City: A WRF/Chem modeling study

Sensitivity of ozone (O₃) concentrations in the Mexico City area to diurnal variations of surface air pollutant emissions is investigated using the WRF/Chem model. Our analysis shows that diurnal variations of nitrogen oxides (NO_x = NO + NO₂) and volatile organic compound (VOC) emissions play an important role in controlling the O₃ concentrations in the Mexico City area. The contributions of NO_x and VOC emissions to daytime O₃ concentrations are very sensitive to the morning emissions of NO_x and VOCs. Increase in morning NO_x emissions leads to decrease in daytime O₃ concentrations as well as the afternoon O₃ maximum, while increase in morning VOC emissions tends to increase in O₃ concentrations in late morning and early afternoon, indicating that O₃ production in Mexico City is under VOC-limited regime. It is also found that the nighttime O₃ is independent of VOCs, but is sensitive to NO_x. The emissions of VOCs during other periods (early morning, evening, and night) have only small impacts on O₃ concentrations, while the emissions of NO_x have important impacts on O₃ concentrations in the evening and the early morning.This study suggests that shifting emission pattern, while keeping the total emissions unchanged, has important impacts on air quality. For example, delaying the morning emission peak from 8 am to 10 am significantly reduced the morning peaks of NO_x and VOCs, as well as the afternoon O₃ maxima. It suggests that without reduction of total emission, the daytime O₃ concentrations can be significantly reduced by changing the diurnal variations of the emissions of O₃ precursors.     

Characterizations of chemical oxidants in Mexico City: A regional chemical dynamical model (WRF-Chem) study

The formation of chemical oxidants, particularly ozone, in Mexico City were studied using a newly developed regional chemical/dynamical model (WRF-Chem). The magnitude and timing of simulated diurnal cycles of ozone (O₃), carbon monoxide (CO) and nitrogen oxides (NO_x)_, and the maximum and minimum O₃ concentrations are generally consistent with surface measurements. Our analysis shows that the strong diurnal cycle in O₃ is mainly attributable to photochemical variations, while diurnal cycles of CO and NO_x mainly result from variations of emissions and boundary layer height. In a sensitivity study, oxidation reactions of aromatic hydrocarbons (HCs) and alkenes yield highest peak O₃ production rates (20 and 18 ppbv h⁻¹, respectively). Alkene oxidations, which are generally faster, dominate in early morning. By late morning, alkene concentrations drop, and oxidations of aromatics dominate, with lesser contributions from alkanes and CO. The sensitivity of O₃ concentrations to NO_x and HC emissions was assessed. Our results show that daytime O₃ production is HC-limited in the Mexico City metropolitan area, so that increases in HC emissions increase O₃ chemical production, while increases in NO_x emissions decrease O₃ concentrations. However, increases in both NO_x and HC emissions yield even greater O₃ increases than increases in HCs alone. Uncertainties in HC emissions estimates give large uncertainties in calculated daytime O₃, while NO_x emissions uncertainties are less influential. However, NO_x emissions are important in controlling O₃ at night.     

Analysis of NO,NO2, O3 and NOx concentrations measured at a green area of Buenos Aires City during wintertime

We analyse the air quality data measured at a green area of Buenos Aires City (Argentina) during 38 days in winter. We study the relationships between ambient concentrations of nitric oxide (NO), nitrogen dioxide (NO₂), ozone (O₃) and nitrogen oxides (NO_x=NO+NO₂). The variation of the level of oxidant (OX=O₃+NO₂) with the NO_x is obtained. It can be seen that the level of OX at a given location is made up of two contributions: one independent and another dependent on the NO_x concentration. The first one can be considered as a regional contribution, equivalent to the background O₃ concentration and the second one as a local contribution that depends on the level of primary pollution. Local oxidant sources may include direct NO₂ emissions, the reaction of NO with O₂ at high-NO_x levels, and the emission of species that promote the conversion of NO to NO₂. The final category of emissions may include the nitrous acid (HONO) that is emitted directly in vehicle exhaust. Finally, we present a diurnal variation of the local as well as regional contributions and the dependence of the last one on wind direction.     

Understanding the Effectiveness of Precursor Reductions in Lowering 8-Hr Ozone Concentrations—Part II. The Eastern United States

Abstract

Analyses of ozone (O₃) measurements in conjunction with photochemical modeling were used to assess the feasibility of attaining the federal 8-hr O₃ standard in the eastern United States. Various combinations of volatile organic compound (VOC) and oxides of nitrogen (NO_x) emission reductions were effective in lowering modeled peak 1-hr O₃ concentrations. VOC emissions reductions alone had only a modest impact on modeled peak 8-hr O₃ concentrations. Anthropogenic NO_x emissions reductions of 46–86% of 1996 base case values were needed to reach the level of the 8-hr standard in some areas. As NO_x emissions are reduced, O₃ production efficiency increases, which accounts for the less than proportional response of calculated 8-hr O₃ levels. Such increases in O₃ production efficiency also were noted in previous modeling work for central California. O₃ production in some urban core areas, such as New York City and Chicago, IL, was found to be VOC-limited. In these areas, moderate NO_x emissions reductions may be accompanied by increases in peak 8-hr O₃ levels. The findings help to explain differences in historical trends in 1- and 8-hr O₃ levels and have serious implications for the feasibility of attaining the 8-hr O₃ standard in several areas of the eastern United States.     

Precursor reductions and ground-level ozone in the Continental United States

Numerous papers analyze ground-level ozone (O₃) trends since the 1980s, but few have linked O₃ trends with observed changes in nitrogen oxide (NO_x) and volatile organic compound (VOC) emissions and ambient concentrations. This analysis of emissions and ambient measurements examines this linkage across the United States on multiple spatial scales from continental to urban. O₃ concentrations follow the general decreases in both NO_x and VOC emissions and ambient concentrations of precursors (nitrogen dioxide, NO₂; nonmethane organic compounds, NMOCs). Annual fourth-highest daily peak 8-hr average ozone and annual average or 98th percentile daily maximum hourly NO₂ concentrations show a statistically significant (p < 0.05) linear fit whose slope is less than 1:1 and intercept is in the 30 to >50 ppbv range. This empirical relationship is consistent with current understanding of O₃ photochemistry. The linear O₃–NO₂ relationships found from our multispatial scale analysis can be used to extrapolate the rate of change of O₃ with projected NO_x emission reductions, which suggests that future declines in annual fourth-highest daily average 8-hr maximum O₃ concentrations are unlikely to reach 65 ppbv or lower everywhere in the next decade. Measurements do not indicate increased annual reduction rates in (high) O₃ concentrations beyond the multidecadal precursor proportionality, since aggressive measures for NO_x and VOC reduction are in place and have not produced an accelerated O₃ reduction rate beyond that prior to the mid-2000s. Empirically estimated changes in O₃ with emissions suggest that O₃ is less sensitive to precursor reductions than is found by the CAMx (v. 6.1) photochemical model. Options for increasing the rate of O₃ change are limited by photochemical factors, including the increase in NO_x sensitivity with time (NMOC/NO_x ratio increase), increase in O₃ production efficiency at lower NO_x concentrations (higher O₃/NO_y ratio), and the presence of natural NO_x and NMOC precursors and background O₃.

Implications:?This analysis demonstrates empirical relations between O₃ and precursors based on long term trends in U.S. locations. The results indicate that ground-level O₃ concentrations have responded predictably to reductions in VOC and NO_x since the 1980s. The analysis reveals linear relations between the highest O₃ and NO₂ concentrations. Extrapolation of the historic trends to the future with expected continued precursor reductions suggest that achieving the 2014 proposed reduction in the U.S. National Ambient Air Quality Standard to a level between 65 and 70 ppbv is unlikely within the next decade. Comparison of measurements with national results from a regulatory photochemical model, CAMx, v. 6.1, suggests that model predictions are more sensitive to emissions changes than the observations would support.     

Measurements of Pollutants inside an Automobile

A series of experiments was conducted to determine the concentration of certain pollutants inside a car under typical driving conditions. The work was performed during the summer months in the Los Angeles area and measurements of O₃, CO, NO, and NO_x were taken. It was found that the O₃ concentration in the passenger compartment may be maintained at relatively low values provided that the influx of outside air is limited. The low levels were explained by decay of O₃ on surfaces within the compartment. The average concentration of the other components inside the car is about equal to that on the outside. In the current tests, however, the measured concentrations did not exceed any of the present standards.     

Major air pollutants in Bursa,Turkey: their levels,temporal changes,interactions, and sources

Bursa is one of the largest cities of Turkey and it hosts 17 organized industrial zones. Parallel to the increase in population, rapidly growing energy consumption, and increased numbers of transport vehicles have impacts on the air quality of the city. In this study, regularly calibrated automatic samplers were employed to get the levels of air pollution in Bursa. The concentrations of CH₄ and N-CH₄ as well as the major air pollutants including PM₁₀, PM_2.5, NO, NO₂, NO_x, SO₂, CO, and O₃, were determined for 2016 and 2017 calendar years. Their levels were 1641.62?±?718.25, 33.11?±?5.45, 42.10?±?10.09, 26.41?±?9.01, 19.47?±?16.51, 46.73?±?16.56, 66.23?±?32.265, 7.60?±?3.43, 659.397?±?192.73, and 51.92?±?25.63 µg/m³ for 2016, respectively. Except for O₃, seasonal concentrations were higher in winter and autumn for both years. O₃, CO, and SO₂ had never exceeded the limit values specified in the regulations yet PM₁₀, PM_2.5, and NO₂ had violated the limits in some days. The ratios of CO/NO_x, SO₂/NO_x, and PM_2.5/PM₁₀ were examined to characterize the emission sources. Generally, domestic and industrial emissions were dominated in the fall and winter seasons, yet traffic emissions were effective in spring and summer seasons. As a result of the correlation process between O_x and NO_x, it was concluded that the most important source of O_x concentrations in winter was NO_x and O₃ was in summer.     

Control of Ozone Precursors in a Complex Industrial Terrain by Using Multiscale-Nested Air Quality Models with Fine Spatial Resolution (1 km2)

Abstract

The location of the northeastern Iberian Peninsula (NEIP) in the northwestern Mediterranean basin, the presence of the Pyrenees mountain range (with altitudes >3000 m), and the influence of the Mediterranean Sea and the large valley canalization of Ebro river induce an extremely complicated structure for the dispersion of photochemical pollutants. Air pollution studies in very complex terrains such as the NEIP require high-resolution modeling for resolving the very complex dynamics of flows. To deal with the influence of larger-scale transport, however, high-resolution models have to be nested in larger models to generate appropriate initial and boundary conditions for the finer resolution domains. This article shows the results obtained through the utilization of the MM5-EMICAT2000-CMAQ multiscale-nested air quality model relating the sensitivity regimes for ozone (O₃)-nitrogen oxides (NO_x)-volatile organic compounds (VOCs) in an area of high geographical complexity, like the industrial area of Tarragona, located in the NEIP. The model was applied with fine temporal (one-hour) and spatial resolution (cells of 24 km, 2 km, and 1 km) to represent the chemistry and transport of tropospheric O₃ and other photochemical species with respect to different hypothetical scenarios of emission controls and to quantify the influence of different emission sources in the area. Results indicate that O₃ chemistry in the industrial domain of Tarragona is strongly sensitive to VOCs; the higher percentages of reduction for ground-level O₃ are achieved when reducing by 25% the emissions of industrial VOCs. On the contrary, reductions in the industrial emissions of NO_x contribute to a strong increase in hourly peak levels of O₃. At the same time, the contribution of on-road traffic and biogenic emissions to ground-level O₃ concentrations in the area is negligible with respect to the pervasive weight of industrial sources. This analysis provides an assessment of the effectiveness of different policies for the control of emission of precursors by comparing the modeled results for different scenarios.     

Gaseous and particulate air pollution in the san gabriel mountains of southern california

In order to assess concentrations and daily patterns of air pollutants at a mountainous site in the South Coast Air Basin, a study was undertaken in the San Dimas Experimental Forest of the San Gabriel Mountains between April 1985 and October 1985. Continuous monitoring of O₃, NO, NO₂, SO₂, total S compounds and light scattering coefficient was conducted. Particulate aerosols were collected twice a week and concentrations of nitrate, ammonium and sulfate in fine (< 2.5 μm diameter) and coarse (> 2.5 μm diameter) modes were determined.For the June–August period, when the levels of photochemical smog were the highest, monthly 24-h average concentrations of the pollutants were: O₃, about 200 μg m⁻³; NO₂, 40–75 μg m⁻³; NO, 1–5 μg m ⁻³; and SO₂, 0.5–5 μgm⁻³. The concentrations of O₃ were about two times higher than in the neighboring stations of the South Coast Air Basin. O₃, SO₂ and total S concentrations peaked in the early afternoon, generally between 1500 and 1600 PST. Peak concentrations of NO occurred in the morning, generally between 1000 and 1100 PST. NO₂ concentrations typically peaked in the late afternoon between 1500 and 1800 PST, but occasionally (in 9 % of days) maximum NO₂ occurred in the morning, concurrently with the NO peaks. Daytime concentrations of the nitrate in fine aerosol fraction were generally between 100 and 600 nEq m ⁻³, those of ammonium between 50 and 300 nEq m ⁻³, and concentrations of sulfate between 60 and 250 nEq m⁻³. A 3-day denuder study showed that HNO₃can make up to 73 % of the total amount of total nitrate in the air. NO₂ was the most abundant N compound at Tan bark Flat (69–86% of the total amount of the monitored N compounds). Nitrate amounted to 9–15 %, HNO₃ to 4–11 %, ammonium to 3–9%, and NO to 1–2% of the total amount of the measured nitrogen compounds.