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1.
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 O 3 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 O 3 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 O 3 concentrations only for a very limited set of conditions in rural areas. 相似文献
2.
Non-methane organic carbon (NMOC) measurements made in Atlanta, Georgia from 1999–2007 are used with nitrogen oxide (NO x or NO y) and ozone (O 3) data to investigate relationships between O 3 precursors and peak 8-hour O 3 concentrations in the city. Data from a WNW-to-ENE transect of sites illustrate that the mean urban peak 8-hour O 3 excess constitutes about 20% of the peak 8-hour O 3 measured at the area-wide maximum O 3 site when air-mass movement is from the northwest quadrant; local influence is potentially greater on days with more stagnation or recirculation. The peak 8-hour O 3 concentrations in Atlanta increase as (1) surface temperature (T), ambient NMOC and NO y concentrations, and previous-day peak O 3 concentrations increase, and as (2) relative humidity, surface wind speeds, and ratios of NMOC-to-NO y decrease. An observation-based statistical model is introduced to relate area-wide peak 8-hour O 3 concentrations to ambient NMOC and NO y concentrations, while accounting for the non-linear dependences of peak 8-hour O 3 concentrations on meteorological factors. On the majority of days when the area-wide peak 8-hour O 3 exceeds 75 ppbv, meteorologically-adjusted peak 8-hour O 3 concentrations increase as ambient NMOC concentrations increase (NMOC sensitive) and ambient NO y concentrations decrease. This result contrasts with regional conditions in which O 3 formation appears to be NO x-sensitive in character. The results offer observationally-based information of relevance to O 3 management strategies in the Atlanta area, potentially contributing to “weight-of-evidence” assessments. 相似文献
3.
This study compares speciated model-predicted concentrations (i.e., mixing ratios) of volatile organic compounds (VOCs) with measurements from the Photochemical Assessment Monitoring Stations (PAMS) network at sites within the northeastern US during June–August of 2006. Measurements of total non-methane organic compounds (NMOC), ozone (O 3), oxides of nitrogen (NO x) and reactive nitrogen species (NO y) are used for supporting analysis. The measured VOC species were grouped into the surrogate classes used by the Carbon Bond IV (CB4) chemical mechanism. It was found that the model typically over-predicted all the CB4 VOC species, except isoprene, which might be linked to overestimated emissions. Even with over-predictions in the CB4 VOC species, model performance for daily maximum O 3 was typically within ±15%. Analysis at an urban site in NY, where both NMOC and NO x data were available, suggested that the reasonable ozone performance may be possibly due to compensating overestimated NO x concentrations, thus modulating the NMOC/NO x ratio to be in similar ranges as that of observations. 相似文献
4.
Ground level ozone represents a significant air quality concern in Toronto, Canada, where the national 65 ppb 8-h standard is repeatedly exceeded during the summer. Here we present an analysis of nitrogen dioxide (NO 2), ozone (O 3), and volatile organic compound (VOC) data from federal and provincial governmental monitoring sites from 2000 to 2007. We show that summertime VOC reactivity and ambient concentrations of NO 2 have decreased over this period of time by up to 40% across Toronto and the surrounding region. This has not resulted in significant summertime ozone reductions, and in some urban areas, it appears to be increasing. We discuss the competing effects of decreased ozone titration leading to an increase in O 3, and decreased local ozone production, both caused by significant decreases in NO x concentrations. In addition, by using local meteorological data, we show that annual variability in summer ozone correlates strongly with maximum daily temperatures, and we explore the effect of atmospheric transport from the southwest which has a significant influence on early morning levels before local production begins. A mathematical model of instantaneous ozone production is presented which suggests that, given the observed decreases in NO x and VOC reactivity, we would not expect a significant change in local ozone production under photochemically relevant conditions. These results are discussed in the context of Toronto's recent commitment to cutting local smog-causing pollutants by 20% by 2012. 相似文献
5.
Air quality impacts of volatile organic compound (VOC) and nitrogen oxide (NO x) emissions from major sources over the northwestern United States are simulated. The comprehensive nested modeling system comprises three models: Community Multiscale Air Quality (CMAQ), Weather Research and Forecasting (WRF), and Sparse Matrix Operator Kernel Emissions (SMOKE). In addition, the decoupled direct method in three dimensions (DDM-3D) is used to determine the sensitivities of pollutant concentrations to changes in precursor emissions during a severe smog episode in July of 2006. The average simulated 8-hr daily maximum O 3 concentration is 48.9 ppb, with 1-hr O 3 maxima up to 106 ppb (40 km southeast of Seattle). The average simulated PM 2.5 (particulate matter with an aerodynamic diameter <2.5 μm) concentration at the measurement sites is 9.06 μg m ?3, which is in good agreement with the observed concentration (8.06 μg m ?3). In urban areas (i.e., Seattle, Vancouver, etc.), the model predicts that, on average, a reduction of NO x emissions is simulated to lead to an increase in average 8-hr daily maximum O 3 concentrations, and will be most prominent in Seattle (where the greatest sensitivity is??0.2 ppb per % change of mobile sources). On the other hand, decreasing NO x emissions is simulated to decrease the 8-hr maximum O 3 concentrations in remote and forested areas. Decreased NO x emissions are simulated to slightly increase PM 2.5 in major urban areas. In urban areas, a decrease in VOC emissions will result in a decrease of 8-hr maximum O 3 concentrations. The impact of decreased VOC emissions from biogenic, mobile, nonroad, and area sources on average 8-hr daily maximum O 3 concentrations is up to 0.05 ppb decrease per % of emission change, each. Decreased emissions of VOCs decrease average PM 2.5 concentrations in the entire modeling domain. In major cities, PM 2.5 concentrations are more sensitive to emissions of VOCs from biogenic sources than other sources of VOCs. These results can be used to interpret the effectiveness of VOC or NO x controls over pollutant concentrations, especially for localities that may exceed National Ambient Air Quality Standards (NAAQS). Implications: The effect of NO x and VOC controls on ozone and PM 2.5 concentrations in the northwestern United States is examined using the decoupled direct method in three dimensions (DDM-3D) in a state-of-the-art three-dimensional chemical transport model (CMAQ). NO x controls are predicted to increase PM 2.5 and ozone in major urban areas and decrease ozone in more remote and forested areas. VOC reductions are helpful in reducing ozone and PM 2.5 concentrations in urban areas. Biogenic VOC sources have the largest impact on O 3 and PM 2.5 concentrations. 相似文献
6.
Numerous papers analyze ground-level ozone (O 3) trends since the 1980s, but few have linked O 3 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. O 3 concentrations follow the general decreases in both NO x and VOC emissions and ambient concentrations of precursors (nitrogen dioxide, NO 2; nonmethane organic compounds, NMOCs). Annual fourth-highest daily peak 8-hr average ozone and annual average or 98th percentile daily maximum hourly NO 2 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 O 3 photochemistry. The linear O 3–NO 2 relationships found from our multispatial scale analysis can be used to extrapolate the rate of change of O 3 with projected NO x emission reductions, which suggests that future declines in annual fourth-highest daily average 8-hr maximum O 3 concentrations are unlikely to reach 65 ppbv or lower everywhere in the next decade. Measurements do not indicate increased annual reduction rates in (high) O 3 concentrations beyond the multidecadal precursor proportionality, since aggressive measures for NO x and VOC reduction are in place and have not produced an accelerated O 3 reduction rate beyond that prior to the mid-2000s. Empirically estimated changes in O 3 with emissions suggest that O 3 is less sensitive to precursor reductions than is found by the CAMx (v. 6.1) photochemical model. Options for increasing the rate of O 3 change are limited by photochemical factors, including the increase in NO x sensitivity with time (NMOC/NO x ratio increase), increase in O 3 production efficiency at lower NO x concentrations (higher O 3/NO y ratio), and the presence of natural NO x and NMOC precursors and background O 3.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 NOx 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. 相似文献
7.
Carbon bond (CB-III) fractions for non-methane organic carbon compounds (NMOC) measured in the background alrmass adverted into several urban areas in the eastern and southern United States are reported. These, together with ozone measured aloft, were used In an Empirical Kinetic Modeling Approach (EKMA) to model urban ozone production and urban ozone control strategies. Over a range of zero to double the mean of the measured NMOC concentrations aloft (0 to 70 ppbC) and zero to the highest ozone levels recorded aloft (0 to 65 ppb), it was found that urban ozone production and control strategies were relatively insensitive to NMOC from aloft. However, urban ozone production was sensitive to ozone from aloft, while ozone control strategies were insensitive to ozone from aloft. 相似文献
8.
Nocturnal chemistry can play an important role in determining the initial morning conditions for daytime chemistry in urban areas. However, the impact on daytime O 3 levels is difficult to assess as the suppression of vertical trace gas transport leads to highly altitude dependent nocturnal chemistry, in particular with respect to the removal and conversion of nitrogen oxides (NO x) and volatile organic compounds (VOC). One-dimensional (1-D) chemical transport model calculations for different nighttime vertical stabilities and different ozone formation regimes (i.e. NO x- vs. VOC-sensitive) were performed assuming a 1000 m high daytime boundary layer and a growing nocturnal boundary layer reaching 200 m height at the end of the night. Exclusion of NO 3 chemistry from the model leads to daytime O 3 concentration changes from ?4% to +16% for different O 3 sensitivities. In all cases strong nocturnal vertical concentration profiles of NO x, O 3, NO 3 and N 2O 5 and a dependence of these profiles on vertical stability were found at night. The nocturnal NO x loss averaged over the lowest 1000 m changes by 9–24% for different vertical stabilities and ozone sensitivities. The impact of nocturnal vertical stability leads to 7–12% difference in O 3 concentration in the morning and ~0–2.5% in the afternoon. 相似文献
9.
Elevated concentrations of ozone, often above the national ambient air quality standard for photochemical oxidants, have been measured in both urban and rural areas of Connecticut. One such episode took place on June 10, 1974. Ozone levels, after stabilizing at values slightly above the standard (i.e., 80 to 110 ppb; Connecticut generated ozone concentrations), rose sharply late in the afternoon reaching concentrations as high as 310 ppb (almost 4 times the standard) in Hartford. The trajectory of the air mass, which arrived in Hartford at the time of maximum O 3 occurence, had its origin in the metropolitan New York area during the early morning rush hour on the episode day. This illustrates that the advective transport of O 3 and O 3 precursors into Connecticut from New York are probably responsible for a significant portion (approximately two-thirds) of the elevated O 3 concentrations measured throughout Connecticut on days when winds are from the south-southwest direction. The fact that peak O 3 levels occur late in the afternoon, several hours after maximum sunlight intensity, reinforces the conclusion that excessive O 3 concentrations developed as O 3 and ozone precursors were generated in the vicinity of New York City and then drifted inland into Connecticut on the afternoon sea breeze. It appears to be unrealistic to develop a hydrocarbon control strategy for Connecticut in order to meet the photochemical oxidant ambient air quality standard when O 3 and/or ozone precursors ad-vectively transported into the State cause oxidant levels to exceed the standard. The complete cessation of all anthropogenic hydrocarbon emissions in Connecticut would not necessarily assure that the standard would be attained here. The implication is that a regional (i.e., the eastern part of the United States) hydrocarbon control strategy is needed to reduce adequately ozone formation and transport so as to allow Connecticut to meet the current oxidant standard. 相似文献
10.
The body of information presented in this paper is directed to those individuals concerned with the effect of urban pollution on downwind areas. Concern has been expressed over the appropriate hydrocarbon and NO x control strategy to be used in minimizing the effects of ozone and NO 2 on urban population centers and their downwind environs. O 3 and NO 2 formation were studied in smog chamber irradiations as a function of the initial NO x concentration at three hydrocarbon concentrations. By carrying out the irradiations for a period of time equivalent to one solar day in a continuously diluting system, smog formation in a chemically reacting pollutant system under transport was simulated. The results of this experimental simulation suggest that hydrocarbon reduction reduces O 3 in urban as well as downwind areas while NO x reduction increases O 3 in the urban area and has little effect on O 3 in downwind areas. Both hydrocarbon and NO x reduction will reduce atmospheric NO 2 levels, with the effect of NO x reduction generally being more pronounced. 相似文献
11.
On hot summer days in the eastern United States, electricity demand rises, mainly because of increased use of air conditioning. Power plants must provide this additional energy, emitting additional pollutants when meteorological conditions are primed for poor air quality. To evaluate the impact of summertime NO x emissions from coal-fired electricity generating units (EGUs) on surface ozone formation, we performed a series of sensitivity modeling forecast scenarios utilizing EPA 2018 version 6.0 emissions (2011 base year) and CMAQ v5.0.2. Coal-fired EGU NO x emissions were adjusted to match the lowest NO x rates observed during the ozone seasons (April 1–October 31) of 2005–2012 (Scenario A), where ozone decreased by 3–4 ppb in affected areas. When compared to the highest emissions rates during the same time period (Scenario B), ozone increased ~4–7 ppb. NO x emission rates adjusted to match the observed rates from 2011 (Scenario C) increased ozone by ~4–5 ppb. Finally in Scenario D, the impact of additional NO x reductions was determined by assuming installation of selective catalytic reduction (SCR) controls on all units lacking postcombustion controls; this decreased ozone by an additional 2–4 ppb relative to Scenario A. Following the announcement of a stricter 8-hour ozone standard, this analysis outlines a strategy that would help bring coastal areas in the mid-Atlantic region closer to attainment, and would also provide profound benefits for upwind states where most of the regional EGU NO x originates, even if additional capital investments are not made (Scenario A). Implications: With the 8-hr maximum ozone National Ambient Air Quality Standard (NAAQS) decreasing from 75 to 70 ppb, modeling results indicate that use of postcombustion controls on coal-fired power plants in 2018 could help keep regions in attainment. By operating already existing nitrogen oxide (NOx) removal devices to their full potential, ozone could be significantly curtailed, achieving ozone reductions by up to 5 ppb in areas around the source of emission and immediately downwind. Ozone improvements are also significant (1–2 ppb) for areas affected by cross-state transport, especially Mid-Atlantic coast regions that had struggled to meet the 75 ppb standard. 相似文献
12.
The effects of the solar eclipse on 11 August 1999 on surface ozone at two sites, Thessaloniki, Greece (urban site) and Hohenpeissenberg, Germany (elevated rural site) are investigated in this study and compared with model results. The eclipse offered a unique opportunity to test our understanding of tropospheric ozone chemistry and to investigate with a simple photochemical box model the response of surface ozone to changes of solar radiation during a photolytical perturbation such as the solar eclipse. The surface ozone measurements following the eclipse display a decrease of around 10–15 ppbv at the urban station of Eptapyrgio at Thessaloniki while at Hohenpeissenberg, the actual ozone data do not show any clear effect of eclipse on surface ozone. For Thessaloniki, the model results suggest that solely photochemistry can account for a significant amount of the observed surface ozone decrease during the eclipse but transport effects mask part of the photochemical effect of eclipse on surface ozone. For Hohenpeissenberg, the box model predicted an ozone decrease, due to the eclipse, of about 2 ppbv in relative agreement with the magnitude of the observed ozone decrease from the 2 h moving average while at the same time it inhibits the foreseen diurnal ozone increase. However, this modeled ozone decrease during the eclipse is small compared to the diurnal ozone variability due to transport effects, and hence, transport really masks such relative small changes. The different magnitude of the surface ozone decrease between the two sites indicates mainly the role of the NO x levels. Measured and modeled NO and NO 2 concentrations at Hohenpeissenberg during the eclipse are also compared and indicate that the partitioning of NO and NO 2 in NO x is influenced clearly from the eclipse. This is not observed at Thessaloniki due to local NO x sources. 相似文献
13.
Abstract The main results of an experimental study focusing on the formation and transport of photochemical pollution in the Madrid air basin are presented. This southern European, heavily populated urban area is located on an elevated plateau at a height of 700 m, near a mountain range with maximum heights of around 2,400 m. Daily and seasonal cycles of ozone were documented during a one-year survey at three semi-rural sites located 30 km away from the urban center. Maximum hourly values of up to 140 ppb were measured, and the ozone generated within the urban plume on polluted days (when values exceeded 90 ppb) has been estimated at around 40-50 ppb.A meteorological characterization of these smoggy days pointed out the influence of thermally induced local wind flows on the concentration daily cycles at the measuring sites, denoting a preferred advection of the urban plume. Moreover, during intensive summer field campaigns, the use of meteorological and ozone sondes, as well as an instrumented aircraft, revealed some features about the horizontal and vertical distribution of the polluted air masses, as well as their evolution within the planetary boundary layer. Ozone plumes have been detected up to 100 km away from the city, usually mixed in a layer that reaches a height of 1,000-1,500 m in the afternoon. On some occasions, ozone-enriched layers have been detected as high as 4,000 m during morning hours, suggesting possible tropospheric injection induced by topographydriven flows or convective mesoscale systems that are usually present in the center of the Iberian Peninsula in the summer. 相似文献
14.
Federal Tier 3 motor vehicle emission and fuel sulfur standards have been promulgated in the United States to help attain air quality standards for ozone and PM 2.5 (particulate matter with an aerodynamic diameter <2.5 μm). The authors modeled a standard similar to Tier 3 (a hypothetical nationwide implementation of the California Low Emission Vehicle [LEV] III standards) and prior Tier 2 standards for on-road gasoline-fueled light-duty vehicles (gLDVs) to assess incremental air quality benefits in the United States (U.S.) and the relative contributions of gLDVs and other major source categories to ozone and PM 2.5 in 2030. Strengthening Tier 2 to a Tier 3-like (LEV III) standard reduces the summertime monthly mean of daily maximum 8-hr average (MDA8) ozone in the eastern U.S. by up to 1.5 ppb (or 2%) and the maximum MDA8 ozone by up to 3.4 ppb (or 3%). Reducing gasoline sulfur content from 30 to 10 ppm is responsible for up to 0.3 ppb of the improvement in the monthly mean ozone and up to 0.8 ppb of the improvement in maximum ozone. Across four major urban areas—Atlanta, Detroit, Philadelphia, and St. Louis—gLDV contributions range from 5% to 9% and 3% to 6% of the summertime mean MDA8 ozone under Tier 2 and Tier 3, respectively, and from 7% to 11% and 3% to 7% of the maximum MDA8 ozone under Tier 2 and Tier 3, respectively. Monthly mean 24-hr PM 2.5 decreases by up to 0.5 μg/m 3 (or 3%) in the eastern U.S. from Tier 2 to Tier 3, with about 0.1 μg/m 3 of the reduction due to the lower gasoline sulfur content. At the four urban areas under the Tier 3 program, gLDV emissions contribute 3.4–5.0% and 1.7–2.4% of the winter and summer mean 24-hr PM 2.5, respectively, and 3.8–4.6% and 1.5–2.0% of the mean 24-hr PM 2.5 on days with elevated PM 2.5 in winter and summer, respectively. Implications: Following U.S. Tier 3 emissions and fuel sulfur standards for gasoline-fueled passenger cars and light trucks, these vehicles are expected to contribute less than 6% of the summertime mean daily maximum 8-hr ozone and less than 7% and 4% of the winter and summer mean 24-hr PM 2.5 in the eastern U.S. in 2030. On days with elevated ozone or PM 2.5 at four major urban areas, these vehicles contribute less than 7% of ozone and less than 5% of PM 2.5, with sources outside North America and U.S. area source emissions constituting some of the main contributors to ozone and PM 2.5, respectively. 相似文献
15.
The Thai Government's search for alternatives to imported petroleum led to the consideration of mandating 10% biofuel blends (biodiesel and gasohol) by 2012. Concerns over the effects of biofuel combustion on ground level ozone formation in relation to their conventional counterparts need addressing. Ozone formation in Bangkok is explored using a trajectory box model. The model is compared against O 3, NO, and NO 2 time concentration data from air monitoring stations operated by the Thai Pollution Control Department. Four high ozone days in 2006 were selected for modeling. Both the traditional trajectory approach and a citywide average approach were used. The model performs well with both approaches but slightly better with the citywide average. Highly uncertain and missing data are derived within realistic bounds using a genetic algorithm optimization. It was found that 10% biofuel substitution will lead to as much as a 16 ppb peak O 3 increase on these four days compared to a 48 ppb increase due to the predicted vehicle fleet size increase between 2006 and 2012. The approach also suggests that when detailed meteorological data is not available to run three dimensional airshed models, and if the air is stagnant or predominately remains over an urban area during the day, that a simple low cost trajectory analysis of O 3 formation may be applicable. 相似文献
16.
Sensitivity of ozone (O 3) 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 + NO 2) and volatile organic compound (VOC) emissions play an important role in controlling the O 3 concentrations in the Mexico City area. The contributions of NO x and VOC emissions to daytime O 3 concentrations are very sensitive to the morning emissions of NO x and VOCs. Increase in morning NO x emissions leads to decrease in daytime O 3 concentrations as well as the afternoon O 3 maximum, while increase in morning VOC emissions tends to increase in O 3 concentrations in late morning and early afternoon, indicating that O 3 production in Mexico City is under VOC-limited regime. It is also found that the nighttime O 3 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 O 3 concentrations, while the emissions of NO x have important impacts on O 3 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 O 3 maxima. It suggests that without reduction of total emission, the daytime O 3 concentrations can be significantly reduced by changing the diurnal variations of the emissions of O 3 precursors. 相似文献
17.
The levels of photochemical air pollutants: O 3, NO and NO 2, were monitored in Athens and in the neighbouring region of the Mesogia plain (Spata, Artemis and Markopoulo) from 1 May–31 August 2000. Phytodetection of ozone was also conducted using bioindicator plants of Bel-W3 and Zichnomirodata (KK6/5) tobacco varieties. The average maximum daily O3 concentration was 60–75 ppb, while the 24 hour average ranged from 40–65 ppb. The AOT40 (ppb hours) index was very high in Athens (16 679 over 121 days), Spata (16 325 over 110 days), Artemis (8093 over 22 days) and Markopoulo (18 646 over 113 days), suggesting potentially phytotoxic ozone levels. The ozone bioindicator plants of Bel-W3 and KK6/5 tobacco varieties were highly injured in all regions confirming the phytotoxicity of those ozone levels. The levels of NO and NO 2 recorded at the three stations, in the Mesogia plain, were considerably lower than those occurring in Athens. The data presented here provide important background information concerning pollution levels in the Mesogia plain shortly before the operation of the new international airport 'Eleftherios Venizelos' in this region (March 2001). 相似文献
18.
In the May and June of 1998, field measurements were taken at a site near the Usery Pass Recreation Area, ∼27 miles from the downtown Phoenix area, overlooking Phoenix and Mesa, Arizona. This site was selected to examine the impacts of the Phoenix urban plume on the Usery Pass Recreation Area and surrounding regions. Data were obtained for ultraviolet-B (UVB) radiation, nitrogen dioxide (NO 2), peroxyacetyl nitrate (PAN), ozone (O 3), and carbon monoxide (CO). Nocturnal plumes of NO 2 (in tens of ppb), observed near midnight, were correlated with CO and anti-correlated with O 3. This behavior was consistent with the titration of locally generated NO by boundary layer O 3 to form the nighttime NO 2 plumes that were subsequently transported into the Usery Pass Recreation area. Nitrate radical (NO 3) production rates were calculated to be very high on the edges of these nocturnal plumes. Examination of O 3 and PAN data also indicates that Phoenix is being affected by long-range transport of pollutants from the Los Angeles to San Diego areas. A regional smoke episode was observed in May, accompanied by a decrease in UVB of factor of two and a decrease in O 3 and an increase in methyl chloride. Low level back trajectories and chemical evidence confirm that the smoke event originated in northern Mexico and that the reduced O 3 levels observed at Usery Pass could be partially due to reduced photolysis rates caused by carbonaceous soot aerosols transported in the smoke plume. The results are discussed with regard to potential effects of local pollution transport from the Phoenix air basin as well as an assessment of the contributions from long-range transport of pollutants to the background levels in the Phoenix-Usery Pass area. 相似文献
19.
This paper summarizes the results of a yearlong continuous measurements of gaseous pollutants, NO, NO 2, NO x and O 3 in the ambient air at Kathmandu valley. Measured concentration of the pollutants in study area is a function of time. NO, NO 2 and O 3 peak occurred in succession in presence of sunlight. At the time of maximum O 3 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 O 3 and NO x, which are evidences of photochemical O 3 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. 相似文献
20.
An investigation of the concentrations of nitrogen oxides (NO X) from an air quality model and observations at monitoring sites was performed to assess the changes in NO X levels attributable to changes in mobile emissions. This evaluation effort focused on weekday morning rush hours since urban NO X concentrations are strongly influenced by the significant loading of emissions associated with heavy commuter traffic. On-road vehicle NO X emissions generated by the MOBILE6 model revealed a steady decline with an overall decrease of 25% for 2002–2006. In this study, a dynamic model evaluation was undertaken that entails an assessment of the predicted concentration response of the Community Multiscale Air Quality (CMAQ) model due to changes in NO X emissions as well as to meteorological variability spanning 3-month summer periods over five consecutive years (2002–2006) against observed concentration changes at NO X monitoring sites located primarily in urban areas of the eastern United States. Both modeled and observed hourly NO X concentrations exhibited maximum values that coincided with the morning peak NO X emissions. The notable results, based on 3-h average (6–9 AM local time) NO X concentrations, derived between the 50th and 95th percentiles of cumulative concentration distributions, revealed that modeled changes at these elevated NO X levels generally tracked the year-to-year variations in the observed concentration changes. When summer 2002 values were used as a reference, both modeled and observed results also showed definitive decreases in weekday morning urban NO X concentrations over this multi-year period, which can be primarily attributed to the reductions in mobile source emissions. Whereas observed NO X concentrations have declined by about 25% over this period consistent with the decline in the modeled mobile emission sector, modeled NO X concentration changes were close to the decreases exhibited in all (mobile + other sectors) surface NO X emissions whose overall decline was about 15% over this multi-year period. 相似文献
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