Source attribution of ozone in Southeast Texas before and after the Deepwater Horizon accident using satellite, sonde, surface monitor, and air mass trajectory data

Since the summer of 2004, over 300 ozonesondes have been launched from Rice University (29.7 N, 95.4 W) or the University of Houston (29.7 N, 95.3 W), each \u3c 5 km from downtown Houston. The Texas Commission on Environmental Quality maintains a large database of hourly surface ozone observations in Southeast Texas. In this study, we identify the contributions to surface ozone pollution levels from natural and anthropogenic sources, both local and remote in nature. This source identification is performed two ways: 1) through an analysis of sonde data, including ozone concentrations, wind speed and direction, and relative humidity data, and 2) through an analysis that combines trajectory calculations with surface monitor data. We also examine regional changes in Ozone Monitoring Instrument (OMI) measurements of formaldehyde and ozone from 2004 – 2010. In particular, we compare the 2010 sonde, surface monitor, and satellite data after the Deepwater Horizon accident with data from previous years to determine the impact, if any, of the large source of hydrocarbons in the Gulf of Mexico on air quality in Southeast Texas

Ozone profile observations in Houston, Texas (1994 - 2010) from aircraft, balloons, and satellites

Houston, Texas has long been an urban area plagued with high levels of surface ozone, particularly in spring and late summer. The combination of a large commuter population and one of the largest concentrations of petrochemical plants in the world results in abundant and nearly co-located sources of NOx and hydrocarbons. The location of Houston on the South Coast of the United States in a subtropical climate results in meteorological conditions that favor ozone production. Using MOZAIC (1994 - 2004), ozonesonde (2000, 2004 - 2010), and TES (2005 – 2010) data, we examine the evolution of ozone profiles over Houston during a period in which various strategies have been implemented to alleviate the ozone pollution problem. Using meteorological data from associated soundings and analyses, we identify and evaluate influences on the ozone profiles from natural and anthropogenic sources, as well as local and remote sources. We further investigate how these various influences have changed with time

Photochemistry in the arctic free troposphere: NOx budget and the role of odd nitrogen reservoir recycling

The budget of nitrogen oxides (NOx) in the arctic free troposphere is calculated with a constrained photochemical box model using aircraft observations from the Tropospheric O3 Production about the Spring Equinox (TOPSE) campaign between February and May. Peroxyacetic nitric anhydride (PAN) was observed to be the dominant odd nitrogen species (NOy) in the arctic free troposphere and showed a pronounced seasonal increase in mixing ratio. When constrained to observed acetaldehyde (CH3CHO) mixing ratios, the box model calculates unrealistically large net NOx losses due to PAN formation (62pptv/day for May, 1-3km). Thus, given our current understanding of atmospheric chemistry, these results cast doubt on the robustness of the CH3CHO observations during TOPSE. When CH3CHO was calculated to steady state in the box model, the net NOx loss to PAN was of comparable magnitude to the net NOx loss to HNO3 (NO2 reaction with OH) for spring conditions. During the winter, net NOx loss due to N2O5 hydrolysis dominates other NOx loss processes and is near saturation with respect to further increases in aerosol surface area concentration. NOx loss due to N2O5 hydrolysis is sensitive to latitude and month due to changes in diurnal photolysis (sharp day-night transitions in winter to continuous sun in spring for the arctic). Near NOx sources, HNO4 is a net sink for NOx; however, for more aged air masses HNO4 is a net source for NOx, largely countering the NOx loss to PAN, N2O5 and HNO3. Overall, HNO4 chemistry impacts the timing of NOx decay and O3 production; however, the cumulative impact on O3 and NOx mixing ratios after a 20-day trajectory is minimal. © 2003 Elsevier Science Ltd. All rights reserved

An investigation of South Pole HOx chemistry: Comparison of model results with ISCAT observations

Unexpected high levels of OH and NO were recorded at the South Pole (SP) Atmospheric Research Observatory during the 1998-99 ISCAT field study. Model simulations suggest a major photochemical linkage between observed OH and NO. A detailed comparison of the observations with model predictions revealed good agreement for OH at NO levels between 120 and 380 pptv. However, the model tended to overestimate OH for NO levels < 120 pptv, while it underestimated OH at levels > 380 pptv. The reasons for these deviations appear not to involve NO directly but rather HOx radical scavenging for the low NO conditions and additional HOx sources for the high NO conditions. Because of the elevated levels of NO and highly activated HOx photochemistry, the SP was found to be a strong net source of surface ozone. It is quite likely that the strong oxidizing environment found at the South Pole extends over the entire polar plateau

Detection of an SO2 plume over Sapporo, Japan from the eruption of Mt. Kasatochi using a balloon sounding technique

During the month of August 2008, 10 ozonesondes were launched from Hokkaido University in Sapporo, Japan as part of a study to examine regional pollution during the Olympic period. Seven of these soundings included a second instrument with a filter designed to remove SO2 from the intake air stream. SO2 interferes with the normal chemistry of the electrochemical cell (ECC) method for ozone detection, with the net result being that each molecule of SO2 registers as minus one molecule of O3. Thus the unfiltered sonde reports [O3] - [SO2] while the filtered sonde reports [O3]. Laboratory tests prior to launch indicate that the SO2 filter is ~87% effective, while destroying little to no O3. The difference between the filtered and unfiltered readings is ~[SO2]. We demonstrate the effectiveness of this technique in the lower and middle troposphere by examining profiles both with and without SO2 present. Ozone Monitoring Instrument (OMI) SO2 data (Krotkov et al., 2006, 2008) and trajectories from the NASA Goddard Trajectory model (Schoeberl & Sparling, 1995) connect the SO2 detected by our balloon borne instruments over Hokkaido, Japan 21 – 22 August to the plume from the volcanic eruption of Mt. Kasatochi 7 – 9 August

Photochemistry in the arctic free troposphere: Ozone budget and its dependence on nitrogen oxides and the production rate of free radicals

Abstract. Local ozone production and loss rates for the arctic free troposphere (58–85 ◦ N, 1–6 km, February–May) during the Tropospheric Ozone Production about the Spring Equinox (TOPSE) campaign were calculated using a constrained photochemical box model. Estimates were made to assess the importance of local photochemical ozone production relative to transport in accounting for the springtime maximum in arctic free tropospheric ozone. Ozone production and loss rates from our diel steady-state box model constrained by median observations were first compared to two point box models, one run to instantaneous steady-state and the other run to diel steady-state. A consistent picture of local ozone photochemistry was derived by all three box models suggesting that differences between the approaches were not critical. Our model-derived ozone production rates increased by a factor of 28 in the 1–3 km layer and a factor of 7 in the 3–6 km layer between February and May. The arctic ozone budget required net import of ozone into the arctic free troposphere throughout the campaign; however, the transport term exceeded the photochemical production only in the lower free troposphere (1–3 km) between February and March. Gross ozone production rates were calculated to increase linearly with NOx mixing ratios up to ∼300 pptv in February and for NOx mixing ratio

Regional-scale chemical transport modeling in support of the analysis of observations obtained during the TRACE-P experiment

Data obtained during the TRACE-P experiment is used to evaluate how well the CFORS/STEM-2K1 regional-scale chemical transport model is able to represent the aircraft observations. Thirty-one calculated trace gas and aerosol parameters are presented and compared to the in situ data. The regional model is shown to accurately predict many of the important features observed. The mean values of all the model parameters in the lowest 1 km are predicted within ±30% of the observed values. The correlation coefficients (R) for the meteorological parameters are found to be higher than those for the trace species. For example, for temperature, R \u3e 0.98. Among the trace species, ethane, propane, and ozone show the highest values (0.8 \u3c R \u3c 0.9), followed by CO, SO2, and NOy, NO and NO2 had the lowest values (R \u3c 0.4). Analyses of pollutant transport into the Yellow Sea by frontal events are presented and illustrate the complex nature of outflow. Biomass burning from SE Asia is transported in the warm conveyor belt at altitudes above ∼2 km and at latitudes below 30N. Outflow of pollution emitted along the east coast of China in the postfrontal regions is typically confined to the lower ∼2 km and results in high concentrations with plume-like features in the Yellow Sea. During these situations the model underpredicts CO and black carbon (among other species). An analysis of ozone production in this region is also presented. In and around the highly industrialized regions of East Asia, where fossil fuel usage dominates, ozone is NMHC-limited. South of ∼30-35N, ozone production is NOx-limited, reflecting the high NMHC/NOx ratios due to the large contributions to the emissions from biomass burning, biogenics sources, and biofuel usage in central China and SE Asia. Copyright 2003 by the American Geophysical Union

An overview of ISCAT 2000

The Investigation of Sulfur Chemistry in the Antarctic Troposphere (ISCAT) took place over the timer period of 15 November to 31 December in the year 2000. The study location was the Amundsen Scott Station in Antarctica. ISCAT 2000 defines the second phase of a program designed to explore tropospheric chemistry in Antarctica. As in 1998, the 2000 ISCAT study revealed a strong oxidizing environment at South Pole (SP). During the 2000 investigation, however, the suite of measurements was greatly expanded. These new measurements established the recycling of reactive nitrogen as a critical component of this unique environment. This paper first presents the historical background leading up to the ISCAT 2000 observations; then it focuses on providing a summary of the year 2000 results and contrasts these with those recorded during 1998. Important developments made during the 2000 study included the recording of SP data for several species being emitted from the snowpack. These included NO, H 2O2 and CH2O. In this context, eddy-diffusion flux measurements provided the first quantitative estimates of the SP NO and NOx snow-to-atmosphere fluxes. This study also revealed that HNO 3 and HO2NO2 were major sink species for HOx and NOx radicals. And, it identified the critical factors responsible for SP NO levels exceeding those at other polar sites by nearly an order of magnitude. Finally, it reports on the levels of gas phase sulfur species and provides evidence indicating that the absence of DMS at SP is most likely due to its greatly shorten chemical lifetime in the near vicinity of the plateau. It is proposed that this is due to the influence of NO on the distribution of OH in the lower free troposphere over a region that extends well beyond the plateau itself. Details related to each of the above findings plus others can be found in the 11 accompanying Special Issue papers. © 2004 Elsevier Ltd. All rights reserved