The ozone increments in urban plumes (original) (raw)
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Regional ozone and urban plumes in the southeastern United States: Birmingham, A case study
Journal of Geophysical Research, 1995
Aircraft measurements of ozone and the oxides of nitrogen have characterized the horizontal and vertical extent of the urban plume downwind of Birmingham, Alabama. Derived NOx emission rate estimates of 0.6 x 1025 molecules s -1, with an uncertainty of a factor of 2, for this metropolitan area are in reasonable accord with the 1985 National Acid Precipitation Assessment Program inventory, which gives 1.2 x 1025 molecules s -1 for daytime emissions. These estimates are from two flights in 1992 when the urban plume was well separated from the plumes from two power plants northwest of the city. During three flights in 1990 the plumes of the Birmingham metropolitan area and the two power plants were combined; good agreement was found between the estimated fluxes1)(2.0 to 5.5 x 102s molecules s -1) and the emission inventory (3.7 x 1025 molecules s-for the combined sources. The enhancement of 03 in the urban plume indicates photochemical formation and shows that during the summertime, approximately seven 03 molecules can be formed per NOx molecule added by the urban and power plant emissions. This production efficiency applies both to the isolated urban plume and to the combined urban-power plant plumes and is similar to that derived for rural areas from surface studies. Comparison of the results from several flights indicates the contribution of the regional ozone levels to the 0 3 concentrations observed within the urban plumes. The aircraft measurements, in combination with surface measurements of ozone, show that the interaction of ozone concentrations entering the urban area, the photochemical formation of ozone during the oxidation of the urban emissions, and the wind speed and direction determine the location and the magnitude of the peak ozone concentrations in the vicinity of this metropolitan area. Paper number 95JD01641. 0148-0227/95/95JD-01641505.00 the urban center [White et al., 1976]. By following the chemical development at successive interceptions of urban plumes, estimates of the oxidation rate of sulfur dioxide [Gillani et al., 1978], the rate of removal of NOx [Spicer, 1982], and the oxidation rate of hydrocarbons [Calvert, 1976; Blake et al., 1993] have been derived. The amount of ozone formed per oxidation of NOx has been estimated in the plumes of large metropolitan areas [White et al., 1983; Altshuller, 1986, and references therein]. Studies of the enhancement of ozone in urban plumes have been summarized by Altshuller [1986].
Journal of Geophysical Research, 1998
A rather limited number of large power plants are responsible for about 2/3 and 1/3 of the U.S. anthropogenic emissions of SO2 and NOx, respectively. Considerable uncertainty continues to prevail about the local and regional impact of their potentially harmful secondary products (e.g., ozone, sulfates, nitrates). We have analyzed state-of-the-art data of the Southern Oxidant Study (SOS)-Nashville Field Study (1994, 1995) for 10 days of summer daytime field measurements by instrumented aircraft in the plumes of three large, tall-stack, base-load, Tennessee Valley Authority (TVA) coal-fired power plants in northwestern Tennessee: Gallatin (G), located within the Nashville urban ozone nonattainment area, and Cumberland (C) and Johnsonville (JV) in rural isoprene-rich forested areas about 100 km to the west of Nashville. The average 1995 emissions of NO• from these three sources ranged over more than an order of magnitude. In this paper, we have explored plume chemical evolution and the magnitude, efficiency, and yield of ozone and NO z (NO• oxidation products, mostly inorganic and organic nitrates) production in a broad variety of plume transport and chemistry scenarios within the convective boundary layer (CBL) in rural and urban settings. The results show that (1) plume chemical maturity and peak production capacities of ozone and NO z were realized quite close to the sources, within 30-40 km and 4 hours of daytime transport for Gallatin (smallest NO• emission rate, QNox, and suburban environment) and typically within 100 km and 6 hours of CBL transport for Cumberland (highest QNox and rural environment rich in isoprene); (2) the ozone impact of Gallatin on Nashville can exceed that of Cumberland, and under favorable transport and chemical conditions, both power plants can contribute as much as 50 ppb of excess ozone to the urban area, raising local peak levels well in excess of 100 ppb; (3) an estimated 3.1 + 0.7 molecules of ozone and more than 0.6 molecules of NO•, may be produced in large isolated rural power plant plumes (PPPs) per molecule of NO• release, and the corresponding peak yields of ozone and NO z may be significantly greater in urban PPPs; (4) the rate of NO z production --10-15% h -• in isolated rural PPPs, and higher in urban PPPs' (5) NO z production is favored in all PPPs at first when the chemistry is VOC-limited; later, with increasing VOC ingestion from the background, the chemistry increasingly favors NO•limited ozone production, starting at plume edges, and ultimately throughout the diluted plume. These results have major implications on outstanding issues related to the environmental impact and regulatory control of electric utility industry NO• emissions.
Ozone production during an urban air stagnation episode over Nashville, Tennessee
Journal of Geophysical Research, 1998
The highest 03 levels observed during the 1995 Southern Oxidants Study in middle Tennessee occurred during a period of air stagnation from July 11 through July 15. Extensive airborne (two fixed wing and one helicopter) and ground-based measurements of the chemistry and meteorology of this episode near Nashville, Tennessee, are presented. In situ airborne measurements include 03, NOy, NO, NO2, SO2, CO, nitrate, hydrocarbons, and aldehydes. Airborne LIDAR 0 3 measurements are also utilized to map the vertical and horizontal extent of the urban plume. The use of multiple instrumented research aircraft permitted highly detailed mapping of the plume chemistry in the vertical and horizontal dimensions. Interactions between the urban Nashville plume (primarily a NOx and hydrocarbon source) and the Gallatin coal-fired power plant plume (primarily a NO x and SO2 source) are also documented, and comparisons of ozone formation in the isolated and mixed urban and power plant plume are presented. The data suggest that during this episode the background air and the edges of the urban plume are NO x sensitive and the core of the urban plume is hydrocarbon sensitive. Under these worst case meteorological conditions, ambient 03 levels well over the level of the new National Ambient Air Quality Standard (NAAQS) for ozone (80 ppb) were observed over and just downwind of Nashville. For example, on July 12, the boundary layer air upwind of Nashville showed 60 to 70 ppb 0 3, while just downwind of the city the urban plume maximum was over 140 ppb 0 3. With a revised ozone standard set at 80 ppb (8 hour average) and upwind levels already within 10 or 20 ppb of the standard, only a slight increase in ozone from the urban area will cause difficulty in attaining the standard at monitors near the core of the urban plume during this type of episode. The helicopter mapping and LIDAR aircraft data clearly illustrate that high O3 levels can occur during stagnation episodes within a few kilometers of and even within the urban area. The extremely light boundary layer winds (1-3 m s-•) contributed to the creation of an ozone dome or blob which stayed very near to the city rather than an elongated plume. The small spatial scale of the zone of high O3 concentrations is mapped in detail demonstrating that the regulatory monitoring network failed to document the maximum O_• concentrations. Modelers using such regulatory data to test photochemical algorithms need to bear in mind that magnitude and frequency of urban ozone may be underestimated by monitoring networks, especially in medium-sized urban areas under slow transport conditions. Finally, this effort shows the value of collaborative field measurements from multiple platforms in developing a more complete picture of the chemistry and transport of photochemical 03. ambient ozone concentrations continue to be a major environmental and health concern. Early in the decade of the 1990s the National Academy of Sciences called for a rethinking of the ozone problem [National Academy of Sciences, 1991], and efforts were redoubled to elucidate the processes of ozone formation and transport in urban and regional settings. On a national level, for example, the North American Research Strategy for Tropospheric Ozone (NARSTO) has been formulated, a focused and coordinated program for the scientific study of tropospheric ozone concentrations, sources, formation mechanisms, and transport across the North American continent. A major emphasis of NARSTO has been the extent to which interregional transport of ozone-rich air masses have affected efforts to attain the NAAQS for ozone. The Southern Oxidant Study (SOS) has provided, in several field studies and observation-based rood-
High urban NO x triggers a substantial chemical downward flux of ozone
Science Advances
Nitrogen oxides (NO x ) play a central role in catalyzing tropospheric ozone formation. Nitrogen dioxide (NO 2 ) has recently reemerged as a key target for air pollution control measures, and observational evidence points toward a limited understanding of ozone in high-NO x environments. A complete understanding of the mechanisms controlling the rapid atmospheric cycling between ozone (O 3 )–nitric oxide (NO)–NO 2 in high-NO x regimes at the surface is therefore paramount but remains challenging because of competing dynamical and chemical effects. Here, we present long-term eddy covariance measurements of O 3 , NO, and NO 2 , over an urban area, that allow disentangling important physical and chemical processes. When generalized, our findings suggest that the depositional O 3 flux near the surface in urban environments is negligible compared to the flux caused by chemical conversion of O 3 . This leads to an underestimation of the Leighton ratio and is a key process for modulating u...
Aerosol and Air Quality Research, 2012
This study investigated the ozone formation mechanism and air mass trajectory via simultaneous air quality sampling around the coastal region of urban Kaohsiung. Vertical concentration profiles of O 3 and its precursors (NO x and VOCs) were sampled and measured at inland and offshore sites during eight intensive sampling periods. The intensive sampling periods were divided into three categories based on meteorological condition: the sea-land breeze period, the northeastern monsoon period, and the mixed period. Vertical profile results showed that the stratification of O 3 was commonly observed at 40 out of 64 sampling sites accounting for 62.5% of the total O 3 measurement. The results obtained from VOCs measurement indicated that the major species of VOCs was acetone, which accounted for 16.25-64.05% of total TVOCs-C 2 in the offshore region, while the major species of VOCs in the inland region was toluene, which accounted for 6.41-43.77 % of total TVOCs-C 2. Backward trajectories showed that air pollutants emitted from land sources could transport to the offshore region, resulting in a high concentration of oversea NO x and VOCs. Major species of VOCs with high O 3 formation potential were found to be aromatics in the low atmosphere around the coastal region of metro Kaohsiung.
Journal of Geophysical Research, 2002
Tropospheric O 3 concentrations are functions of the chain lengths of NO x (NO x NO + NO 2) and HO x (HO x OH + HO 2 + RO 2) radical catalytic cycles. For a fixed HO x source at low NO x concentrations, kinetic models indicate the rate of O 3 production increases linearly with increases in NO x concentrations (NO x limited). At higher NO x concentrations, kinetic models predict ozone production rates decrease with increasing NO x (NO x saturated). We present observations of NO, NO 2 , O 3 , OH, HO 2 , H 2 CO, actinic flux, and temperature obtained during the 1999 Southern Oxidant Study from June 15 to July 15, 1999, at Cornelia Fort Airpark, Nashville, Tennessee. The observations are used to evaluate the instantaneous ozone production rate (P O3) as a function of NO abundances and the primary HO x production rate (P HOx). These observations provide quantitative evidence for the response of P O3 to NO x. For high P HOx (0.5 < P HOx < 0.7 ppt/s), O 3 production at this site increases linearly with NO to $500 ppt. P O3 levels out in the range 500-1000 ppt NO and decreases for NO above 1000 ppt. An analysis along chemical coordinates indicates that models of chemistry controlling peroxy radical abundances, and consequently P O3 , have a large error in the rate or product yield of the RO 2 + HO 2 reaction for the classes of RO 2 that predominate in Nashville. Photochemical models and our measurements can be forced into agreement if the product of the branching ratio and rate constant for organic peroxide formation, via RO 2 + HO 2 ! ROOH + O 2 , is reduced by a factor of 3-12. Alternatively, these peroxides could be rapidly photolyzed under atmospheric conditions making them at best a temporary HO x reservoir. This result implies that O 3 production in or near urban areas with similar hydrocarbon reactivity and HO x production rates may be NO x saturated more often than current models suggest.
Characterization of the Nashville urban plume on July 3 and July 18, 1995
Journal of Geophysical Research, 1998
This paper reports results from the Southern Oxidants Study field campaign designed to characterize the formation and distribution of ozone and related species in the Nashville urban region. Data from several airborne platforms as well as surface observations on July 3 and 18 are examined to gain insight into the factors that control 03 formation rates and concentrations in the regional plumes. On both days, well-defined urban and power plant plumes were sampled. Utilizing both aircraft and surface data, a detailed kinetic analysis of the chemical evolution of the urban plume is performed to derive NOx lifetime, ozone production efficiency, OH concentration, HNO3 dry deposition rate, and the relative importance of natural and anthropogenic hydrocarbons to 03 production. Analysis of the urban plume data revealed a very active photochemical system (average [OH]-1.2 x 10 '/molecules cm-3) which consumed 50% of the NOx within approximately 2 hours, at an ozone production efficiency of 2.5 to 4 molecules for each molecule of NOx. Anthropogenic hydrocarbons provided approximately 44% of the fuel for ozone production by the urban plume. The dry deposition rate for HNO3 in the urban plume was estimated to be of the order of 5 to 7 cm s-•. 1. Introduction Similar to many urban areas in the southeastern United States, Nashville has had difficulty attaining compliance with current National Ambient Air Quality Standards for 03 Although standard 03 control strategies have been implemented for some time, 03 levels in the southeastern United States have not decreased measurably [Chameides et al., 1992; Chameides and Cowling, 1995]. The 1995 Southern Oxidants Study (SOS-Nashville/Mid Tennessee) was part of an effort to unravel the process of ozone production [Natio•ml Academy of Sciences, 1991] so that different emission control strategies could be investigated [Sillman, 1993]. Nashville is a moderately sized city with a population of 0.5 million people in the downtown and surrounding metropolitan area. It is the only major metropolitan area in central Tennessee and for this reason air quality is not significantly influenced by transport of fresh emissions from other urban areas. However,
Tropospheric layering of ozone in regions of urbanized complex and/or coastal terrain: a review
Progress in Physical Geography, 2000
Exchange of pollutants between the atmospheric boundary layer and free troposphere is an important (yet often neglected) process that tends to produce distinct layers of pollution in the lower troposphere. These layers represent a potential sink for pollutants from the boundary layer, have the potential to be mixed to ground and likely influence tropospheric chemistry and the global climate system.
The impact of anthropogenic and biogenic emissions on surface ozone concentrations in Istanbul
Surface ozone concentrations at Istanbul during a summer episode in June 2008 were simulated using a high resolution and urban scale modeling system coupling MM5 and CMAQ models with a recently developed anthropogenic emission inventory for the region. Two sets of base runs were performed in order to investigate for the first time the impact of biogenic emissions on ozone concentrations in the Greater Istanbul Area (GIA). The first simulation was performed using only the anthropogenic emissions whereas the second simulation was performed using both anthropogenic and biogenic emissions. Biogenic NMVOC emissions were comparable with anthropogenic NMVOC emissions in terms of magnitude. The inclusion of biogenic emissions significantly improved the performance of the model, particularly in reproducing the low night time values as well as the temporal variation of ozone concentrations. Terpene emissions contributed significantly to the destruction of the ozone during nighttime. Biogenic NMVOCs emissions enhanced ozone concentrations in the downwind regions of GIA up to 25 ppb. The VOC/NO x ratio almost doubled due to the addition of biogenic NMVOCs. Anthropogenic NO x and NMVOCs were perturbed by ± 30% in another set of simulations to quantify the sensitivity of ozone concentrations to the precursor emissions in the region. The sensitivity runs, as along with the model-calculated ozone-to-reactive nitrogen ratios, pointed NO x-sensitive chemistry, particularly in the downwind areas. On the other hand, urban parts of the city responded more to changes in NO x due to very high anthropogenic emissions.
Surface ozone measurements and meteorological influences in the urban atmosphere of Istanbul
International Journal of Environment and Pollution, 2002
Hourly measurements of ozone concentration in the urban atmosphere of Istanbul were carried out from February 1998 to July 1999. An assessment of the annual variations and relationships of ozone concentrations and meteorological variables was made. Annual variations were first examined without considering meteorological variables, then meteorological influences on ozone seasonal values were examined. Furthermore, a typical ozone threshold period was analysed by considering meteorological variables for a case study. Meteorological conditions favourable for high ozone concentrations appeared when Istanbul and its surrounding region were dominated by an anticyclonic pressure system. During conducive ozone days, southerly and southwesterly winds with low speeds (daytime mean value <11m1s −1) influence Istanbul.