Regional Ozone Production Research Articles

Sensitivities of NO<sub>x</sub> transformation and the effects on surface ozone and nitrate

Abstract. As precursors to tropospheric ozone and nitrate, nitrogen oxide (NOx) in the present atmosphere and its transformation in response to emission and climate perturbations are studied by using the CAM-Chem model and air quality measurements from the National Emissions Inventory (NEI), Clean Air Status and Trends Network (CASTNET), and Environmental Protection Agency Air Quality System (EPA AQS). It is found that NOx transformations in present atmospheric conditions show different sensitivities over industrial and non-industrial regions. As a result, the surface ozone and nitrate formations can be divided into several regimes associated with the dominant emission types and relative levels of NOx and volatile organic compounds (VOC). Ozone production in industrial regions (the main NOx emission source areas) increases in warmer conditions and slightly decreases following an increase in NOx emissions due to NOx titration, which is opposite to the response in non-industrial regions. The ozone decrease following a temperature increase in non-industrial regions indicates that ozone production in regions that lack NOx emission sources may be sensitive to NOx transformation in remote source regions. The increase in NO2 from NOx titration over industrial regions results in an increase rate of total nitrate that remains higher than the increase rate of NOx emissions. The presented findings indicate that a change in the ozone concentration is more directly affected by changes in climate and precursor emissions, while a change in the nitrate concentration is affected by local ozone production types and their seasonal transfer. The sensitivity to temperature perturbations shows that a warmer climate accelerates the decomposition of odd nitrogen (NOy) during the night. As a result, the transformation rate of NOx to nitrate decreases. Examinations of the historical emissions and air quality records of a typical NOx-limited area, such as Atlanta and a VOC-limited area, such as Los Angeles further confirm the conclusions drawn from the modeling experiments.

Evaluation of an urban NMHC emission inventory by measurements and impact on CTM results

This paper presents an evaluation of the consistency of an urban state-of-the-art hydrocarbon (HC) emission inventory. The evaluation was conducted through the comparison of this inventory with hourly HC measurements during two summer months in the centre of Marseille, on the Mediterranean French coast. Factors of under or overestimation could be calculated for each compound on the basis of a systematic HC to HC ratio analysis. These results, associated with a deep analysis of the speciation profiles, show that most of the common and highly concentrated hydrocarbons (such as butanes) are too much predominant in the emission speciation, while the heavy and less common species (branched alkanes, substituted aromatics) are under-represented in the inventory. The urban diffuse sources appear here as one critical point of the inventories. The disagreements were shown to have a strong incidence on the representation of the air mass reactivity. In a last step, the identified uncertainties in emissions were implemented in an air-quality model for sensitivity studies. It was shown that the observed biases in the inventory could affect the regional ozone production, with a probable impact on ozone peaks of 2–10 ppbv over the area.

Global tropospheric ozone modeling: Quantifying errors due to grid resolution

Ozone production in global chemical models is dependent on model resolution because ozone chemistry is inherently nonlinear, the timescales for chemical production are short, and precursors are artificially distributed over the spatial scale of the model grid. In this study we examine the sensitivity of ozone, its precursors, and its production to resolution by running a global chemical transport model at four different resolutions between T21 (5.6° × 5.6°) and T106 (1.1° × 1.1°) and by quantifying the errors in regional and global budgets. The sensitivity to vertical mixing through the parameterization of boundary layer turbulence is also examined. We find less ozone production in the boundary layer at higher resolution, consistent with slower chemical production in polluted emission regions and greater export of precursors. Agreement with ozonesonde and aircraft measurements made during the NASA TRACE‐P campaign over the western Pacific in spring 2001 is consistently better at higher resolution. We demonstrate that the numerical errors in transport processes on a given resolution converge geometrically for a tracer at successively higher resolutions. The convergence in ozone production on progressing from T21 to T42, T63, and T106 resolution is likewise monotonic but indicates that there are still large errors at 120 km scales, suggesting that T106 resolution is too coarse to resolve regional ozone production. Diagnosing the ozone production and precursor transport that follow a short pulse of emissions over east Asia in springtime allows us to quantify the impacts of resolution on both regional and global ozone. Production close to continental emission regions is overestimated by 27% at T21 resolution, by 13% at T42 resolution, and by 5% at T106 resolution. However, subsequent ozone production in the free troposphere is not greatly affected. We find that the export of short‐lived precursors such as NOx by convection is overestimated at coarse resolution.

3D Ozone Production In Relation To VOCEmission And Oxidation, And The Assessment Of2010 Ozone Control Strategies

In order to efficiently reduce the number and intensity of ozone regional peaks, a regulation centered on the diminution of VOC and NOx emissions was promoted for 2010 in many European countries. In this paper we present a study of the respective role of anthropogenic and biogenic VOCs on regional ozone production, in order to determine the species most involved in local ozone production and their geographical and temporal impact on ozone production rates. Through a 3Dmodelling case study, we derived the participation in ozone production of the main precursor species (VOCs, CO) from the chemical scheme by the use of inert tracers. The results highlight the important role of biogenic emissions as expected, but also the strong participation of CO, and that of aromatic species and light alkenes as initiators of ozone production close to sources. This study is part of a larger project aiming to simulate 2010 regional scenarios. The same tracer studies will be conducted on 2010 projected emissions to evaluate from a detailed analysis of the ozone production mechanisms the efficiency of the engaged regulation.

Chemical transport model ozone simulations for spring 2001 over the western Pacific: Regional ozone production and its global impacts

The spatial and temporal variation in ozone production over major source regions in East Asia during the NASA Transport and Chemical Evolution over the Pacific (TRACE‐P) measurement campaign in spring 2001 is assessed using a global chemical transport model. There is a strong latitudinal gradient in ozone production in springtime, driven by regional photochemistry, which rapidly diminishes as the season progresses. The great variability in meteorological conditions characteristic of East Asia in springtime leads to large daily variability in regional ozone formation, but we find that it has relatively little impact on the total global production. We note that transport processes effectively modulate and thus stabilize total ozone production through their influence over its location. However, the impact on the global ozone burden, important for assessing the effects of precursor emissions on tropospheric oxidizing capacity and climate, is sensitive to local meteorology through the effects of location on chemical lifetime. Stagnant, anticyclonic conditions conducive to substantial boundary layer ozone production typically allow little lifting of precursors into the free troposphere where greater ozone production could occur, and the consequent shorter chemical lifetime for ozone leads to relatively small impacts on global ozone. Conversely, cyclonic conditions with heavy cloud cover suppressing regional ozone production are often associated with substantial cloud convection, enhancing subsequent production in the free troposphere where chemical lifetimes are longer, and the impacts on global ozone are correspondingly greater. We find that ozone formation in the boundary layer and free troposphere outside the region of precursor emissions dominates total gross production from these sources in springtime, and that it makes a big contribution to the long range transport of ozone, which is greatest in this season.

Airborne measurements of isoprene, CO, and anthropogenic hydrocarbons and their implications

Measurements of the mixing ratios of light hydrocarbons (≥C6) were made aboard the National Oceanic and Atmospheric Administration Lockheed Orion WP‐3 aircraft during June and July of 1994 and 1995 during a series of flights over the region around Nashville, Tennessee. The measurements were carried out as part of the Nashville/Middle Tennessee Study of the Southern Oxidant Study (SOS) whose purpose was to describe the sources, variation, and distribution of ozone and its precursors in the southeastern United States during the summer season. The spatial (altitude and latitude) distribution of isoprene and anthropogenic nonmethane hydrocarbons (NMHCs) is described. The isoprene distribution measured within the planetary boundary layer over the region is compared to the recent inventories. The correlations between the various anthropogenic hydrocarbons are used to demonstrate the combined influence of OH photochemistry and dilution on their concentrations. Finally, the distributions of those NMHCs that were measured are compared to those of CO and methane and discussed in terms their implications for odd hydrogen photochemistry and our understanding of regional ozone production. In the boundary layer, OH reactions are dominated by isoprene in the southern part of the region explored and by CO and methane in the northern part. The other measured NMHCs are seen to play only a minor role in ozone production in the nonurban atmosphere.

Ozone formation and transport in southeastern United States: Overview of the SOS Nashville/Middle Tennessee Ozone Study

The Southern Oxidants Study (SOS) is a public‐private partnership collectively engaged, since 1989, in a coordinated program of policy‐relevant research to improve scientific and public understanding of tropospheric ozone pollution. In the summers of 1994 and 1995, SOS implemented the Nashville/Middle Tennessee Ozone Study. This effort, the second SOS urban intensive study, conducted a series of integrated, process‐oriented airborne and surface measurement experiments to better understand the chemistry and meteorology associated with the production, transport, and impact of tropospheric ozone. Specific technical objectives addressed (1) the role of biogenic VOC and NOx emissions on local and regional ozone production, (2) the effect of urban‐rural exchange/interchange on local and regional ozone production, (3) sub‐grid‐scale photochemical and meteorological processes, and (4) the provision of a high‐quality chemical and meteorological data set to test and improve observation‐ and emission‐based air quality forecast models. Some of the more significant findings of the 1994–1995 studies include the following: (1) Ozone production in Nashville was found to be close to the transition between NOx‐sensitive and VOC‐sensitive chemistry. (2) Ozone production efficiency (OPE) in power plant plumes, molecules of ozone formed per molecule of NOx emitted, was found to be inversely proportion to NOx emission rate, with the plants having the greatest NOx emissions exhibiting the lowest OPE. (3) During stagnant conditions, nighttime winds dominated pollutant transport and represent the major mechanism for transporting urban pollutants to rural areas. Ultimately, results provided by this research will allow improved assessment of existing ozone management strategies and provide better scientific tools for the development of future management strategies.

Measurements of PAN, PPN, and MPAN made during the 1994 and 1995 Nashville Intensives of the Southern Oxidant Study: Implications for regional ozone production from biogenic hydrocarbons

Isoprene and a variety of other reactive hydrocarbons are released in large quantities by vegetation in forested regions and are thought to participate in the NOx‐catalyzed production of ozone, a serious air quality problem in North America and Europe [National Research Council, 1991]. The determination of the fraction of O3 formed from anthropogenic NOx and biogenic hydrocarbons (BHC) is a crucial step in the formulation of effective control strategies. Peroxymethacrylic nitric anhydride (MPAN, CH2C(CH3)C(O)OONO2) is formed almost entirely from the atmospheric oxidation of isoprene in the presence of NOx and is an excellent indicator of recent ozone production from isoprene and therefore biogenic hydrocarbons. Measurements are presented here of MPAN, peroxyacetic nitric anhydride (PAN, CH3C(O)OONO2), peroxypropionic nitric anhydride (PPN, CH3CH2C(O)OONO2) and ozone from separate data sets acquired during the 1994 and 1995 Nashville intensive studies of the Southern Oxidant Study. It was found that PAN, a general product of HC‐NOx photochemistry, could be well represented as a simple linear combination of contributions from BHC and anthropogenic hydrocarbon (AHC) chemistries as indicated by MPAN and PPN, respectively. The PAN:MPAN ratios found to be characteristic of BHC‐dominated chemistry ranged from 6 to 10. The PAN:PPN ratios found to be characteristic of AHC‐dominated chemistry ranged from 5.8 to 7.4. These BHC and AHC attributions were used to estimate the contributions of anthropogenic and biogenic hydrocarbons to regional tropospheric ozone production, and substantial BHC‐O3 (50–60 ppbv) was estimated in cases where high NOx from power plants was present in areas of high BHC emission. This estimation method provides direct evidence of significant photochemical ozone production from the oxidation of biogenic hydrocarbons in the presence of NOx.

Shenandoah Cloud and Photochemistry Experiment (SCAPE): Overview

The Shenandoah Cloud and Photochemistry Experiment (SCAPE) investigated the chemistry of the atmosphere at a high‐elevation forested site in central Virginia with particular focus on the factors controlling concentrations of ozone, carbonyl compounds, and carboxylic acids. Carbonyl compounds and carboxylic acids are ubiquitous chemical constituents of the global troposphere, but many aspects of their biogeochemical cycling are poorly understood. Carbonyls are generated from the oxidation of hydrocarbons; formaldehyde (HCHO) produced via this pathway is an important precursor for OH. Thus the carbonyls are intermediates in and tracers of tropospheric photochemistry [e.g., Carlier et al., 1988]. Carboxylic acids are major natural sources of atmospheric acidity thereby partially controlling pH‐dependent chemical transformations in clouds [e.g., Keene and Galloway, 1988]. The aqueous‐phase oxidation of HCHO in clouds has been hypothesized as a significant source of formic acid (HCOOH) and the aqueous‐phase oxidation of HCOO− a potentially important in‐cloud sink for OH [Chameides and Davis, 1983; Jacob, 1986]. Under many conditions, clouds should be a net sink for tropospheric HCOOH [Jacob and Wofsy, 1988]. Specific research objectives were (1) to assess the relative importance of NOx and hydrocarbons in limiting regional ozone production, (2) to investigate sources and sinks for carbonyl compounds and caiboxylic acids, and (3) to examine the droplet‐size dependence of solute concentrations and the thermodynamics of phase partitioning for carbonyl compounds and carboxylic acids in clouds.

A one-year record of ozone profiles in an Alpine valley (Zillertal/Tyrol, Austria, 600–2000 m a.s.l.)

Our data, based on ozone records in the year 1987 in an Alpine valley at elevations from 600 m to 2000 m a.s.l. indicate the existence of increased ozone levels from March to September in the experimental region. These levels were observed at a height range of 400–1400 m above the floor of the valley and exhibit monthly averaged ozone values of typically 5–20 ppbv above the ‘mid-tropospheric’ (3000 m a.s.l.) concentrations. The excess ozone gives evidence for an additional effect of local and regional ozone production in additon to the general influx of ozone from the free troposphere. Considering recent views about the historical trends of ozone increase at ground level and in the free troposphere we found that ozone levels at elevated sites in the northern parts of the Eastern Alps have more than doubled since the 1950s. At an elevation of 1000 m a.s.l. in the Zillertal (400 m above the floor of the valley) the increase is near a factor of three.