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1.
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?=?O 3?+?NO 2), 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, NO 2 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 O 3 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 [NO 2]/[OX] and [NO 2]/[NO x ] vs. [NO x ] were analysed to find the fraction of OX in the form of NO 2, and the possible source of the local NO x -dependent contribution, respectively. The progressive increase of the ratio [NO 2]/[OX] with [NO x ] observed shows a greater proportion of OX in the form of NO 2 as the level of NO x increases. The higher measured values in the ratio [NO 2]/[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 NO 2 photolysis, J NO2?=?0.18–0.64 min ?1, a key atmospheric reaction that influence O 3 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. 相似文献
2.
Significant differences occur between results of chamber work conducted outdoors versus work conducted indoors under constant light intensity. Under outdoor conditions at constant [NO X] O, lower [HC]o resulted in lower [NO 2] max and NO 2 dosage during the daylight hours. The percent reduction in [NO 2] max was a function of the [HC] 0 reduction and the [NO X] O level. Under all experimental conditions the 10 hour N0 2 average to maximum N0 2 concentration ratio appeared to be constant at 0.73 during the daylight hours. A regression equation relating [NO x] max to [NO X] O, [HC] O, and measures of solar radiation accounted for 92% of the variance in the data. Although there is unavoidable confoundment between [HC] 0 and solar radiation, the HC term in this regression equation can introduce ±20 % change in [N0 2] max - This variation can be partially offset or enhanced by variations in solar radiation. 相似文献
3.
This study considered effects of reduced [O 3] on wheat yield. Open-top chamber charcoal filtered air treatments were compared with non-filtered treatments for field-grown wheat. 30 experiments meeting requirements were found, representing nine countries in North America, Europe and Asia. 26 experiments reported improved yield and 4 experiments reduced yield by filtration, a significant positive effect. Average yield improvement was 9%. Average daytime [O 3] was reduced by filtration from 35 to 13 nmol mol −1. Filtration efficiency was 63% for O 3 and 56% for SO 2. For NO x it was observed that NO 2 was reduced and NO increased by filtration. Thus, filters convert NO 2 to NO. Most experiments reported low or very low [SO 2] and [NO x]. Thus, O 3 can be concluded to be the main phytotoxic component in the experiments. Elevated [NO 2] was observed in one experiment. The conclusion is that current [O 3] over large parts of the world adversely affect wheat yield. 相似文献
4.
Abstract The ozone (O 3) sensitivity to nitrogen oxides (NO x, or nitric oxide [NO] + nitrogen dioxide [NO 2]) 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 O 3/NO y (where NO y represents the sum of NO + NO 2 + nitric acid [HNO 3] + peroxyacetyl nitrate [PAN] + others), NO y, and the semiempirically derived O 3/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 O 3, 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 O 3/NO y, O 3/NO z surrogate, and NO y in MCMA suggest that O 3 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 O 3 in Mexico City is NO x-sensitive. Simulated MCMA-derived sensitive transition values for O 3/NO y, hydrogen peroxide (H 2O 2)/HNO 3, 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 O 3/NO z and O 3/HNO 3 was not consistent with values reported elsewhere. An additional empirical evaluation of weekend/weekday differences in average maximum O 3 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 O 3 levels. 相似文献
5.
We evaluated the effect of a 20% reduction in the rate constant of the reaction of the hydroxyl radical with nitrogen dioxide to produce nitric acid (OH+NO 2→HNO 3) on model predictions of ozone mixing ratios ([O 3]) and the effectiveness of reductions in emissions of volatile organic compounds (VOC) and nitrogen oxides (NO x) for reducing [O 3]. By comparing a model simulation with the new rate constant to a base case scenario, we found that the [O 3] increase was between 2 and 6% for typical rural conditions and between 6 and 16% for typical urban conditions. The increases in [O 3] were less than proportional to the reduction in the OH+NO 2 rate constant because of negative feedbacks in the photochemical mechanism. Next, we used two different approaches to evaluate how the new OH+NO 2 rate constant changed the effectiveness of reductions in emissions of VOC and NO x: first, we evaluated the effect on [O 3] sensitivity to small changes in emissions of VOC (d[O 3]/d EVOC) and NO x (d[O 3]/d ENOx); and secondly, we used the empirical kinetic modeling approach to evaluate the effect on the level of emissions reduction necessary to reduce [O 3] to a specified level. Both methods showed that reducing the OH+NO 2 rate constant caused control strategies for VOC to become less effective relative to NO x control strategies. We found, however, that d[O 3]/d EVOC and d[O 3]/d ENOx did not quantitatively predict the magnitude of the change in the control strategy because the [O 3] response was nonlinear with respect to the size of the emissions reduction. We conclude that model sensitivity analyses calculated using small emissions changes do not accurately characterize the effect of uncertainty in model inputs (in this case, the OH+NO 2 rate constant) on O 3 attainment strategies. Instead, the effects of changes in model inputs should be studied using large changes in precursor emissions to approximate realistic attainment scenarios. 相似文献
6.
In this study, air pollutants, including ozone (O 3), nitrogen oxides (NO x = NO + NO 2), carbon monoxides (CO), sulfur dioxide (SO 2), and volatile organic compounds (VOCs) measured in the Yangtze River Delta (YRD) region during several air flights between September/30 and October/11 are analyzed. This measurement provides horizontal and vertical distributions of air pollutants in the YRD region. The analysis of the result shows that the measured O 3 concentrations range from 20 to 60 ppbv. These values are generally below the US national standard (84 ppbv), suggesting that at the present, the O 3 pollutions are modest in this region. The NO x concentrations have strong spatial and temporal variations, ranging from 3 to 40 ppbv. The SO 2 concentrations also have large spatial and temporal variations, ranging from 1 to 35 ppbv. The high concentrations of CO are measured with small variations, ranging from 3 to 7 ppmv. The concentrations of VOCs are relatively low, with the total VOC concentrations of less than 6 ppbv. The relative small VOC concentrations and the relative large NO x concentrations suggest that the O 3 chemical formation is under a strong VOC-limited regime in the YRD region. The measured O 3 and NO x concentrations are strongly anti-correlated, indicating that enhancement in NO x concentrations leads to decrease in O 3 concentrations. Moreover, the O 3 concentrations are more sensitive to NO x concentrations in the rural region than in the city region. The ratios of Δ[O 3]/Δ[NO x] are ?2.3 and ?0.25 in the rural and in the city region, respectively. In addition, the measured NO x and SO 2 concentrations are strongly correlated, highlighting that the NO x and SO 2 are probably originated from same emission sources. Because SO 2 emissions are significantly originated from coal burnings, the strong correlation between SO 2 and NO x concentrations suggests that the NO x emission sources are mostly from coal burned sources. As a result, the future automobile increases could lead to rapid enhancements in O 3 concentrations in the YRD region. 相似文献
7.
Abstract A computer model called the Ozone Risk Assessment Model (ORAM) was developed to evaluate the health effects caused by ground-level ozone (O 3) exposure. ORAM was coupled with the U.S. Environmental Protection Agency’s (EPA) Third-Generation Community Multiscale Air Quality model (Models-3/CMAQ), the state-of-the-art air quality model that predicts O 3 concentration and allows the examination of various scenarios in which emission rates of O 3 precursors (basically, oxides of nitrogen [NO x] and volatile organic compounds) are varied. The principal analyses in ORAM are exposure model performance evaluation, health-effects calculations (expected number of respiratory hospital admissions), economic valuation, and sensitivity and uncertainty analysis through a Monte Carlo simulation. As a demonstration of the system, ORAM was applied to the eastern Tennessee region, and the entire O 3 season was simulated for a base case (typical emissions) and three different emission scenarios. The results indicated that a synergism occurs when reductions in NO x emissions from mobile and point sources were applied simultaneously. A 12.9% reduction in asthma hospital admissions is expected when both mobile and point source NO x emissions are reduced (50 and 70%, respectively) versus a 5.8% reduction caused by mobile source and a 3.5% reduction caused by point sources when these emission sources are reduced individually. 相似文献
8.
Because investigations of PAN at higher southern latitudes are very scarce, we measured surface PAN concentrations for the first time in Antarctica. During the Photochemical Experiment at Neumayer (PEAN'99) campaign mean surface PAN mixing ratios of 13±7 pptv and maximum values of 48 pptv were found. When these PAN mixing ratios were compared to the sum of NO x and inorganic nitrate they were found to be equal or higher. Low ambient air temperatures and low PAN concentrations caused a slow homogeneous PAN decomposition rate of approximately 5×10 −2 pptv h −1. These slow decay rates were not sufficient to firmly establish the simultaneously observed NO x concentrations. In addition, low concentration ratios of [HNO 3]/[NO x] imply that the photochemical production of NO x within the snow pack can influence surface NO x mixing ratios in Antarctica. Alternate measurements of PAN mixing ratios at two different heights above the snow surface were performed to derive fluxes between the lower troposphere and the underlying snow pack using calculated friction velocities. Most of the concentration differences were below the precision of the measurements. Therefore, only an upper limit for the PAN flux of ±1×10 13 molecules m −2 s −1 without a predominant direction can be estimated. However, PAN fluxes below this limit can still influence both the transfer of nitrogen compounds between atmosphere and ice, and the PAN budget in higher southern latitudes. 相似文献
9.
The purpose of this work is to investigate the behaviour and variability of oxidant levels (OX?=?NO 2?+?O 3), 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 O 3 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 NO 2 increases with the increase in NO x concentration during the day. The higher proportion of NO 2 observed at night must be due to the conversion of NO to NO 2 by the NO?+?O 3 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?+?O 2?=?2NO 2, at high-NO x levels and stagnant air during several days. Finally, we estimated the photolysis rate of NO 2, 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. 相似文献
10.
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
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.
Based on hourly measurements of NO x NO 2 and O 3 and meteorological data, an ordinary least squares (OLS) model and a first-order autocorrelation (AR) model were developed to analyse the regression and prediction of NO x and NO 2 concentrations in London. Primary emissions and wind speed are the most important factors influencing NO x concentrations; in addition to these two, reaction of NO with O 3 is also a major factor influencing NO 2 concentrations. The AR model resulted in high correlation coefficients ( R > 0.95) for the NO x and NO 2 regression based on a whole year's data, and is capable of predicting NO 2 ( R = 0.83) and NO x ( R = 0.65) concentrations when the explanatory variables were available. The analysis of the structure of regression models by Principal Component Analysis (PCA) indicates that the regression models are stable. The results of the OLS model indicate that there was an exceptional NO 2 source, other than primary emission and reaction of NO with O 3, in the air pollution episode in London in December 1991. 相似文献
13.
Aircraft observations from three recent missions (STRAT, SUCCESS, SONEX) are synthesized into a theoretical analysis of the factors controlling the concentrations of HO x radicals (HO x=OH+peroxy) and the larger reservoir family HO y (HO y=HO x+2H 2O 2+2CH 3OOH+HNO 2+HNO 4) in the upper troposphere. Photochemical model calculations capture 66% of the variance of observed HO x concentrations. Two master variables are found to determine the variance of the 24 h average HO x concentrations: the primary HO x production rate, P(HO x), and the concentration of nitrogen oxide radicals (NO x=NO+NO 2). We use these two variables as a coordinate system to diagnose the photochemistry of the upper troposphere and map the different chemical regimes. Primary HO x production is dominated by the O( 1D)+H 2O reaction when [H 2O]>100 ppmv, and by photolysis of acetone (and possibly other convected HO x precursors) under drier conditions. For the principally northern midlatitude conditions sampled by the aircraft missions, the HO x yield from acetone photolysis ranges from 2 to 3. Methane oxidation amplifies the primary HO x source by a factor of 1.1–1.9. Chemical cycling within the HO x family has a chain length of 2.5–7, while cycling between the HO x family and its HO y reservoirs has a chain length of 1.6–2.2. The number of ozone molecules produced per HO y molecule consumed ranges from 4 to 12, such that ozone production rates vary between 0.3 and 5 ppbv d −1 in the upper troposphere. Three chemical regimes (NO x-limited, transition, NO x-saturated) are identified to describe the dependence of HO x concentrations and ozone production rates on the two master variables P(HO x) and [NO x]. Simplified analytical expressions are derived to express these dependences as power laws for each regime. By applying an eigenlifetime analysis to the HO x–NO x–O 3 chemical system, we find that the decay of a perturbation to HO y in the upper troposphere (as from deep convection) is represented by four dominant modes with the longest time scale being factors of 2–3 times longer than the steady-state lifetime of HO y. 相似文献
14.
Monitoring data from the UK Automatic Urban and Rural Network are used to investigate the relationships between ambient levels of ozone (O 3), nitric oxide (NO) and nitrogen dioxide (NO 2) as a function of NO x, for levels ranging from those typical of UK rural sites to those observed at polluted urban kerbside sites. Particular emphasis is placed on establishing how the level of ‘oxidant’, OX (taken to be the sum of O 3 and NO 2) varies with the level of NO x, and therefore to gain some insight into the atmospheric sources of OX, particularly at polluted urban locations. The analyses indicate that the level of OX at a given location is made up of NO x-independent and NO x-dependent contributions. The former is effectively a regional contribution which equates to the regional background O 3 level, whereas the latter is effectively a local contribution which correlates with the level of primary pollution. The local oxidant source has probable contributions from (i) direct NO 2 emissions, (ii) the thermal reaction of NO with O 2 at high NO x, and (iii) common-source emission of species which promote NO to NO 2 conversion. The final category may include nitrous acid (HONO), which appears to be emitted directly in vehicle exhaust, and is potentially photolysed to generate HO x radicals on a short timescale throughout the year at southern UK latitudes. The analyses also show that the local oxidant source has significant site-to-site variations, and possible reasons for these variations are discussed. Relationships between OX and NO x, based on annual mean data, and fitted functions describing the relative contributions to OX made by NO 2 and O 3, are used to define expressions which describe the likely variation of annual mean NO 2 as a function of NO x at 14 urban and suburban sites, and which can take account of possible changes in the regional background of O 3. 相似文献
15.
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
16.
We have used a three-dimensional off-line chemical transport model (CTM) to assess the impact of lightning emissions in the free troposphere both on NO x itself and on other chemical species such as O 3 and OH. We have investigated these effects using two lightning emission scenarios. In the first, lightning emissions are coupled in space and time to the convective cloud top height calculated every 6 h by the CTM's moist convection scheme. In the second, lightning emissions are calculated as a constant, monthly mean field. The model's performance against observed profiles of NO x and O 3 in the Atlantic and Pacific ocean improves significantly when lightning emissions are included. With the inclusion of these emissions, the CTM produces a significant increase in the NO x concentrations in the upper troposphere, where the NO x lifetime is long, and a smaller increase in the lower free troposphere, where the surface NO x sources dominate. These changes cause a significant increase in the O 3 production in the upper troposphere and hence higher calculated O 3 there. The model indicates that lightning emissions cause local increases of over 50 parts per 10 12 by volume (pptv) in NO x, 200 pptv in HNO 3 and 20 parts per 10 9 by volume (ppbv) (>40%) in O 3. In addition, a smaller increase of O 3 in the lower troposphere occurs due to an increase in the downward transport of O 3. The O 3 change is accompanied by an increase in OH which is more pronounced in the upper troposphere with a corresponding reduction in CO. The method of emission employed in the model does not appear to have a significant effect globally. In the upper troposphere (above about 300 hPa) NO x concentrations are generally lower with monthly mean emissions, because of the de-coupling of emissions from the model's convection scheme, which vents NO x aloft more efficiently in the coupled scheme. Below the local convective outflow altitude, NO x concentrations are larger when using the monthly mean emissions than when coupled to the convection scheme, because the more dilute emissions, and nighttime emissions, lead to a slower NO x destruction rate. Only minor changes are predicted in the monthly average fields of O 3 if we emit lightning as a monthly constant field. However, the method of emission becomes important when we make a direct comparison of model results with time varying data. These differences should be taken into account when a direct comparison of O 3 with measurements collected at particular times and locations is attempted. 相似文献
17.
Abstract Data from the U.S. Environmental Protection Agency Air Quality System, the Southeastern Aerosol Research and Characterization database, and the Assessment of Spatial Aerosol Composition in Atlanta database for 1999 through 2002 have been used to characterize error associated with instrument precision and spatial variability on the assessment of the temporal variation of ambient air pollution in Atlanta, GA. These data are being used in time series epidemiologic studies in which associations of acute respiratory and cardiovascular health outcomes and daily ambient air pollutant levels are assessed. Modified semivariograms are used to quantify the effects of instrument precision and spatial variability on the assessment of daily metrics of ambient gaseous pollutants (SO 2, CO, NO x, and O 3) and fine particulate matter ([PM 2.5] PM 2.5 mass, sulfate, nitrate, ammonium, elemental carbon [EC], and organic carbon [OC]). Variation because of instrument imprecision represented 7–40% of the temporal variation in the daily pollutant measures and was largest for the PM 2.5 EC and OC. Spatial variability was greatest for primary pollutants (SO 2, CO, NO x, and EC). Population–weighted variation in daily ambient air pollutant levels because of both instrument imprecision and spatial variability ranged from 20% of the temporal variation for O 3 to 70% of the temporal variation for SO 2 and EC. Wind rose plots, corrected for diurnal and seasonal pattern effects, are used to demonstrate the impacts of local sources on monitoring station data. The results presented are being used to quantify the impacts of instrument precision and spatial variability on the assessment of health effects of ambient air pollution in Atlanta and are relevant to the interpretation of results from time series health studies that use data from fixed monitors. 相似文献
18.
Measurement of NO 2 and NO has been carried out in Piedmont, N. C. and in the southern Appalachian Mountains. Average values for the Piedmont were: continuous NO 2 measured 30 ft above surface, 0.76 pphm (14.3 μg/m 3), 1 20 ft, 0.61 pphm (11.5 μg/m 3); simultaneous values (also Piedmont) (2-hr discrete samples) taken at an earlier time at 4 ft, NO 2, 0.56 pphm (10.6 μg/m 3), NO, 0.19 pphm (2.34 μg/m 3). The mountain top values (5120 ft, 1573 m) were: NO 2, 0.46 pphm (6.4 μg/m 3), NO, 0.26 pphm (2.72 μg/m 3). The results of this study furnish further proof that tropospheric NO and NO 2 are produced at the surface of the earth. Data obtained are consistent with the belief that a major sink for NO x is reaction with O3 and ultimate conversion to nitrate. Ozone values frequently increased and NO x values decreased ahead of cold fronts, probably as a result of deep vertical mixing. Also, in small scale turbulence the changes in NO x values and in the O 3 values tended to be “out of phase,” i.e., as O 3 concentration increased, NO x concentration decreased and vice versa. Values of NO x from Green Knob, N. C. (mountain top) also tended to be higher at times when O 3 values were lowest. The NO 2 hourly average values in Piedmont, N. C, demonstrated a diurnal cycle reminiscent of diurnal urban changes. An early morning peak was followed by a minimum in mid-afternoon. Next, the values rose to a broad evening peak and then decreased slowly during the night. Reported urban concentrations are usually about ten times those found in Piedmont, N. C. 相似文献
19.
An observation-based method (OBM) is developed to evaluate the ozone (O 3) production efficiency (O 3 molecules produced per NO x molecule consumed) and O 3 production rate ( P(O 3)) during a field campaign in southern Taiwan. The method can also provide an estimate of the concentration of OH. A key step in the method is to use observed concentrations of two aromatic hydrocarbons, namely ethylbenzene and m, p-xylene, to estimate the degree of photochemical processing and amounts of photochemically consumed NO x and NMHCs by OH. In addition, total oxidant (O 3+NO 2) instead of O 3 itself turns out to be very useful for representing ozone production in the OBM approach. The average O 3 production efficiency during the field campaign in Fall (2003) is found to be about 10.2±3.9. The relationship of P(O 3) with NO x is examined and compared with a one-dimensional (1D) photochemical model. Values of P(O 3) derived from the OBM are slightly lower than those calculated in the 1D model. However, OH concentrations estimated by the OBM are about a factor of 2 lower than the 1D model. Fresh emissions, which affect the degree of photochemical processing appear to be a major cause of the underestimate. We have developed a three-dimensional (3D) OBM O 3 production diagram that resembles the EKMA ozone isopleth diagram to study the relationship of the total oxidant versus O 3 precursors. The 3D OBM O 3 production diagram suggests that reducing emissions of NMHCs are more effective in controlling O 3 than reducing NO x. However, significant uncertainties remain in the OBM, and considerable more work is required to minimize these uncertainties before a definitive control strategy can be reached. The observation-based approach provides a good alternative to measuring peroxy radicals for evaluating the production of O 3 and formulating O 3 control strategy in urban and suburban environments. 相似文献
20.
In the OZIPP (ozone isopleth plotting package, developed by United States Environmental Protection Agency) a number of model specific assumptions with respect to chemical and physical processes are made. These assumptions are introduced into an alternative model developed at AERE Harwell, United Kingdom, in which a detailed chemistry and mixture of organic emissions is included. The impact on the AERE Harwell model results of the assumptions made in OZIPP of omitting ground removal of ozone (O 3) and peroxyacetylnitrate (PAN) and of employing an incomplete PAN chemistry and adopting a reaction rate coefficient of the key reaction NO + HO 2 → NO 2 + OH which is a factor 10 lower than the accepted value, are discussed. The composition of the organic emissions is an important model parameter, and it is shown how grouping of nonmethane hydrocarbon (NMHC) emissions into a small group of NMHC thought to be representative, often implies that O 3 and other pollutants are overestimated. The O 3 isopleth diagram for London constructed using the AERE Harwell model gives a somewhat different picture from that obtained with OZIPP. OZIPP in general predicts that NO x control or combined hydrocarbon(HC) and NO x control is efficient with respect to O 3 reduction whilst the AERE Harwell model predicts that HC control alone usually is more efficient than combined HC and NO x control. Furthermore NO x control alone may often increase the O 3 burden downwind in the AERE Harwell model. 相似文献
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