B. F. Taubman

Intercontinental Chemical Transport Experiment Ozonesonde Network Study (IONS) 2004: 1. Summertime upper troposphere/lower stratosphere ozone over northeastern North America

Coordinated ozonesonde launches from the Intercontinental Transport Experiment (INTEX) Ozonesonde Network Study (IONS) (http://croc.gsfc.nasa.gov/intex/ions.html) in July-August 2004 provided nearly 300 O3 profiles from eleven North American sites and the R/V Ronald H. Brown in the Gulf of Maine. With the IONS period dominated by low-pressure conditions over northeastern North America (NENA), the free troposphere in that region was frequently enriched by stratospheric O3. Stratospheric O3 contributions to the NENA tropospheric O3 budget are computed through analyses of O3 laminae (Pierce and Grant, 1998; Teitelbaum et al., 1996), tracers (potential vorticity, water vapor), and trajectories. The lasting influence of stratospheric incursions into the troposphere is demonstrated, and the computed stratospheric contribution to tropospheric column O3 over the R/V Ronald H. Brown and six sites in Michigan, Virginia, Maryland, Rhode Island, and Nova Scotia, 23% ± 3%, is similar to summertime budgets derived from European O3 profiles (Collette and Ancellet, 2005). Analysis of potential vorticity, Wallops ozonesondes (37.9°N, 75.5°W), and Measurements of Ozone by Airbus In-service Aircraft (MOZAIC) O3 profiles for NENA airports in June-July-August 1996–2004 shows that the stratospheric fraction in 2004 may be typical. Boundary layer O3 at Wallops and northeast U.S. sites during IONS also resembled O3 climatology (June-July-August 1996–2003). However, statistical classification of Wallops O3 profiles shows the frequency of profiles with background, nonpolluted boundary layer O3 was greater than normal during IONS.

Airborne Characterization of the Chemical, Optical, and Meteorological Properties, and Origins of a Combined Ozone-Haze Episode over the Eastern United States

Airborne observations of trace gases, particle size distributions, and particle optical properties were made during a constant altitude transect from New Hampshire to Maryland on 14 August 2002, the final day of a multiday haze and ozone (O3) episode over the Mid-Atlantic and northeastern United States. These observations, together with chemical, meteorological, and dynamical analyses, suggest that a simple two-reservoir model, composed of the lower free troposphere (LFT), where photochemical processes are accelerated and removal via deposition does not occur, and the planetary boundary layer (PBL), where most precursor species are injected, may realistically represent the physics and chemistry of severe, multiday haze and O 3 episodes over the Mid

The 2003 North American electrical blackout: An accidental experiment in atmospheric chemistry

:0305 Atmospheric Composition and Structure: Aerosols andparticles (0345, 4801); 0315 Atmospheric Composition andStructure: Biosphere/atmosphere interactions; 0368 AtmosphericComposition and Structure: Troposphere—constituent transportand chemistry; 3307 Meteorology and Atmospheric Dynamics:Boundary layer processes; 6620 Public Issues: Science policy.Citation: Marufu, L. T., B. F. Taubman, B. Bloomer, C. A.Piety, B. G. Doddridge, J. W. Stehr, and R. R. Dickerson (2004),The 2003 North American electrical blackout: An accidentalexperiment in atmospheric chemistry, Geophys. Res. Lett., 31,L13106, doi:10.1029/2004GL019771.

Convective and Wave Signatures in Ozone Profiles Over the Equatorial Americas: Views from TC4 (2007) and SHADOZ

[1] During the TC4 (Tropical Composition, Clouds, and Climate Coupling) campaign in July–August 2007, daily ozonesondes were launched over coastal Las Tablas, Panama (7.8°N, 80°W) and several times per week at Alajuela, Costa Rica (10°N, 84°W). Wave activity, detected most prominently in 100–300 m thick ozone laminae in the tropical tropopause layer, occurred in 50% (Las Tablas) and 40% (Alajuela) of the soundings. These layers, associated with vertical displacements and classified as gravity waves (GW, possibly Kelvin waves) by laminar identification, occur with similar structure and frequency over the Paramaribo (5.8°N, 55°W) and San Cristobal (0.92°S, 90°W) Southern Hemisphere Additional Ozonesondes (SHADOZ) sites. GW‐labeled laminae in individual soundings correspond to cloud outflow as indicated by DC‐8 tracers and other aircraft data, confirming convective initiation of equatorial waves. Layers representing quasi‐ horizontal displacements, referred to as Rossby waves by the laminar technique, are robust features in soundings from 23 July to 5 August. The features associated with Rossby waves correspond to extratropical influence, possibly stratospheric, and sometimes to pollution transport. Comparison of Las Tablas and Alajuela ozone budgets with 1999– 2007 Paramaribo and San Cristobal soundings shows that TC4 is typical of climatology for the equatorial Americas. Overall during TC4, convection and associated waves appear to dominate ozone transport in the tropical tropopause layer; intrusions from the extratropics occur throughout the free troposphere.

Reply to comment by D. A. Hansen et al. on ''The 2003 North American electrical blackout: An accidental experiment in atmospheric chemistry''

[1] We thank Hansen et al. [2005] for their interest in our letter, ‘‘The 2003 North American electrical blackout: An accidental experiment in atmospheric chemistry’’ and appreciate the opportunity to expand upon the original, necessarily brief publication. We begin by making corrections to some apparent factual misrepresentations in their comment and then go on to provide a point-by-point response. [2] . Contrary to Hansen et al’s [2005] contention we do not base our inferences and conclusions on a single comparison of measurements performed on August 15, 2003 and August 4, 2002. We also compare measurements inside to measurements outside the blackout area on the same day, August 15, 2003. [3] . Reductions in power plant emissions that we report were not ‘‘estimated’’ as stated in the comment but are based on measurements made by power plants and reported to the USEPA. This was pointed out and referenced in the paper. [4] . We do not conclude, as suggested in the comment, that the observed improvements in air quality went on to benefit much of the ‘‘United States’’ but rather ‘‘much of the eastern United States’’. These are completely different statements. [5] Hansen et al. [2005] state the most important limitation of our study as being ‘‘. . . failure to consider the variability associated with concentrations of atmospheric species’’. They further state that similarity in synoptic weather patterns does not mean similarity in concentrations. However, the authors do not spell out what concentration variability considerations we overlooked nor do they attempt to qualify the statements. Complexities of atmospheric processes notwithstanding, it is not unreasonable to assume that when factors that drive transport and, subsequent physical and chemical transformation of pollutants in the air masses are similar, the concentrations of both primary and secondary atmospheric pollutants should be similar, unless of course, as obtained on August 15, 2003, a major primary pollutant source is perturbed. [6] Hansen et al. [2005] compare observed ozone maps from EPA’s AirNow archives for August 4, 2002 (our control day) and August 14, 2003; a day they contend was synoptically similar to our experimental day (August 15, 2003). They go on to argue that since O3 levels over Maryland, Pennsylvania, and New Jersey on August 4, 2002 were higher than on August 14, 2003 our observed changes in air quality following the blackout could have been a result of phenomena other than reduction in power plant emissions. This argument does not hold because in choosing the control day (August 4, 2002) we did not only consider synoptic-scale air motion but all factors that drive atmospheric chemical and physical processes, including temperature, insolation, and humidity. The average regional surface high temperature for August 14, 2003 ( 29 C) was about 4 C lower than that for August 4, 2002 ( 33 C) or August 15 2003 ( 33 C). Ryan et al. [1999] show that in this temperature range, a 4 C difference can account for as much as 35 ppb in O3, probably enough to account for the unspecified disparity in O3 abundance that Hansen et al. report. Ozone concentrations on August 14, 2003 cannot, therefore, be compared to August 4, 2002 or August 15, 2003. Local meteorology cannot be responsible for the differences in air quality observed in our study because surface O3 maps from EPA’s AirNow archives also show the same differences at the regional level. [7] Regarding the regional representativeness of measurements conducted over a single location, we would like to point out that unlike surface measurements, which Hansen et al. [2005] probably had in mind, aircraft vertical profiles (surface – 3 km) are more regional measurements that capture regional signatures. Moreover, our overall deductions are not based only on the profiles conducted over central PA but on transects and profiles conducted over PA, northern Virginia, and Maryland as well. The PM2.5 comparisons, which Hansen et al. go on to make in support of the representativeness argument, are wrong for the following reasons: [8] 1) As alluded to earlier, the days they compare (August 14 and August 15, 2003) are not synoptically similar. [9] 2) The PM2.5 data presented are 24-hour averages, therefore August 14, 2003 data were also affected (lowered) by the blackout, which started at 4:00 ET on the same day. Thus a comparison of 24-hour average PM2.5 concentrations GEOPHYSICAL RESEARCH LETTERS, VOL. 32, L10813, doi:10.1029/2005GL022385, 2005