D. K. Nicks

Evaluation of GOME satellite measurements of tropospheric NO2 and HCHO using regional data from aircraft campaigns in the southeastern United States

[1] We compare tropospheric measurements of nitrogen dioxide (NO2) and formaldehyde (HCHO) from the Global Ozone Monitoring Experiment (GOME) satellite instrument with in situ measurements over eastern Texas and the southeast United States. On average, the GOME and in situ measurements of tropospheric NO2 and HCHO columns are consistent despite pronounced sampling differences. The geometric mean in situ to GOME ratios over the campaign are 1.08 for NO2 and 0.84 for HCHO, with corresponding geometric standard deviations of 1.27 and 1.38. The correlation of the observed column spatial variability between the two NO2 measurement sets is encouraging before (r 2 = 0.54, n = 18) and after (r 2 = 0.67, n = 18) correcting for a sampling bias. Mean relative vertical profiles of HCHO and NO2 calculated with a global three-dimensional model (GEOS-CHEM) and used in the GOME retrieval are highly consistent with in situ measurements; differences would affect the retrieved NO2 and HCHO columns by a few percent. GOME HCHO columns over eastern Texas include contributions from anthropogenic volatile organic compound (VOC) emissions but are dominated by biogenic VOC emissions at the regional scale in August–September when HCHO columns are within 20% of those over the southeastern United States. In situ measurements show that during summer the lowest 1500 m (the lower mixed layer) contains 75% of the tropospheric NO2 column over Houston and Nashville, and 60% of the HCHO column over Houston. Future validation of space-based measurements of tropospheric NO2 and HCHO columns over polluted regions should include coincident in situ measurements that span the entire satellite footprint, especially in the heterogeneous mixed layer. INDEX TERMS: 0315 Atmospheric Composition and Structure: Biosphere/atmosphere interactions; 0322 Atmospheric Composition and Structure: Constituent sources and sinks; 0345 Atmospheric Composition and Structure: Pollution—urban and regional (0305); 0365 Atmospheric Composition and Structure: Troposphere— composition and chemistry; 0394 Atmospheric Composition and Structure: Instruments and techniques;

Measurement of peroxycarboxylic nitric anhydrides (PANs) during the ITCT 2K2 aircraft intensive experiment

[1] Measurements of peroxycarboxylic nitric anhydrides (PANs), peroxyacetic nitric anhydride (CH3C(O)OONO2; PAN), and peroxypropionic nitric anhydride (CH3CH2C(O)OONO2; PPN) were made in the spring of 2002, off the west coast of North America, as part of the Intercontinental Transport and Chemical Transformation 2002 (ITCT 2K2) project. Long-range transport of Asian emissions was observed in which PAN and PPN mixing ratios were as high as 650 pptv and 90 pptv, respectively. Moreover, these two species constituted as much as 80% of the odd nitrogen (NOy) in those air masses, and median PAN/NOy was more than 60% at altitudes of 4 km and above. Systematic differences in the ratio of PPN to PAN were observed in air masses that had been impacted by Asian urban emissions relative to those impacted by biomass burning. Mixing ratios of PAN and PPN were also elevated in the marine boundary layer close to the west coast of California, possibly because of photochemical production driven by maritime NOx emissions. INDEX TERMS: 0368 Atmospheric Composition and Structure: Troposphere—constituent transport and chemistry; 0365 Atmospheric Composition and Structure: Troposphere—composition and chemistry; 0345 Atmospheric Composition and Structure: Pollution—urban and regional (0305); KEYWORDS: peroxyacetic nitric anhydride, Asian pollution, eastern Pacific

Fossil-fueled power plants as a source of atmospheric carbon monoxide

Elevated carbon monoxide (CO) mixing ratios in excess of those derived from emissions inventories have been observed in plumes from one gas- and coal-fired power plant and three of four lignite coal-fired electric utility power plants observed in east and central Texas. Observations of elevated CO on days characterized by differing wind directions show that CO emissions from the lignite plants were relatively constant over time and cannot be ascribed to separate sources adjacent to the power plants. These three plants were found to be emitting CO at rates 22 to 34 times those tabulated in State and Federal emissions inventories. Elevated CO emissions from the gas- and coal-fired plant were highly variable on time scales of hours to days, in one case changing by a factor of 8 within an hour. Three other fossil-fueled power plants, including one lignite-fired plant observed during this study, did not emit substantial amounts of CO, suggesting that a combination of plant operating conditions and the use of lignite coal may contribute to the enhanced emissions. Observed elevated CO emissions from the three lignite plants, if representative of average operating conditions, represent an additional 30% of the annual total CO emissions from point sources for the state of Texas.

Measuring reactive nitrogen emissions from point sources using visible spectroscopy from aircraft

Accurate measurements of nitrogen dioxide (NO2), a key trace gas in the formation and destruction of tropospheric ozone, are important in studies of urban pollution. Nitrogen dioxide column abundances were measured during the Texas Air Quality Study 2000 using visible absorption spectroscopy from an aircraft. The method allows for quantification of the integrated total number of nitrogen dioxide molecules in the polluted atmosphere and is hence a useful tool for measuring plumes of this key trace gas. Further, we show how such remote-sensing observations can be used to obtain information on the fluxes of nitrogen dioxide into the atmosphere with unique flexibility in terms of aircraft altitude, and the height and extent of mixing of the boundary layer. Observations of nitrogen dioxide plumes downwind of power plants were used to estimate the flux of nitrogen oxide emitted from several power plants in the Houston and Dallas metropolitan areas and in North Carolina. Measurements taken over the city of Houston were also employed to infer the total flux from the city as a whole.

Intercomparison of total ozone observations at Fairbanks, Alaska, during POLARIS

The pattern of seasonal ozone loss over Fairbanks, Alaska (AK), during the NASA Photochemistry of Ozone Loss in the Arctic Region In Summer (POLARIS) campaign in the spring and summer of 1997 is defined. Five independent data sets of total ozone observations at Fairbanks are presented, from the Earth Probe and ADEOS Total Ozone Mapping Spectrometer (TOMS) satellite instruments, balloon-borne electrochemical concentration cell ozonesondes, and ground-based (Brewer spectroradiometer, Dobson spectrophotometer, and the Jet Propulsion Laboratory MkIV infrared interferometer) instruments. The excellent agreement between different observational techniques lends confidence to the observed rate of summertime loss of total ozone at high latitudes. In addition, the small offsets between the data sets are well understood.

Development and evaluation of the diffusion denuder‐sulfur chemiluminescence detector for atmospheric SO2 measurements

The University of Alaska Fairbanks participated in the Gas-Phase Sulfur Intercomparison Experiment (GASIE) to evaluate the sulfur chemiluminescence detector (SCD). The SCD is a relatively new sulfur selective detection technology (Benner and Stedman, 1989, 1990, 1994; Benner, 1991; Stedman and Benner, 1995). The system used during GASIE is referred to as the diffusion denuder/sulfur chemiluminescence detector (DD/SCD). We chose to use a diffusion denuder to separate SO2 from other sulfur species rather than a gas chromatograph because one of our long-term goals is to develop the DD/SCD into a unique system capable of resolving low pptv levels of SO2 on timescales of 1 min or less. The principles of detection of the DD/SCD and how it was operated during GASIE are presented. Results from the GASIE program are presented in detail by Stecher et al. (this issue). In this paper, we briefly describe what was learned about the diffusion DD/SCD technique from GASIE. To address the problems revealed, the DD/SCD has been completely redesigned and rigorously tested in our laboratory. The modifications made, how these modification eliminate many of the problems found during GASIE, and results form subsequent laboratory testing are discussed.

Gas-Phase sulfur intercomparison Experiment 2: Analysis and conclusions

A diffusion denuder, total sulfur chemiluminescence detector instrument for the measurement of SO2 was tested as the second part of the Gas-Phase Sulfur Intercomparison Experiment (GASIE 2). The SO2 at mixing ratios between 27 and 182 parts per trillion by volume (pptv) was provided by a dynamic dilution apparatus. The data were kept blind from the other party and analyzed by two independent referees. The following was concluded: (1) The independent calibrations of each system are within a few percent. (2) The precision on any one day is better than day-to-day variability. (3) Runs in dry air show a small but significant nonzero intercept in correlation plots. (4) No effects of adding NO2 + O3 or CO2 + CH4 + CO + dimethylsulfide are distinguishable. (5) A small but significant effect due to added H2O is evident in both slope and intercept, but the source could not be discerned. (6) On any one day the systems can distinguish among 0, 20, and 40 pptv, but because of day-to-day variability, they can only distinguish among 0, 30, and 60 pptv on different days.

Subminute measurements of SO2 at low parts per trillion by volume mixing ratios in the atmosphere

The continuous sulfur dioxide detector (CSD) is a sensitive instrument for reliable measurements at high time resolution in the atmosphere. This new instrument is based on a SO2 measurement technique utilizing the sulfur chemiluminescence detector, previously validated in a rigorously blind experiment sponsored by the National Science Foundation. Simplified sample handling, denuder separation technology, and the intrinsic sensitivity and fast response of the detector permit measurement at levels below 100 parts per trillion by volume in tens of seconds with the CSD. The CSD provides a differential measurement where response from ambient SO2 is determined by the difference between air containing SO2 and air scrubbed of SO2, where both air samples contain other detectable sulfur species. Digital signal post processing with phase-locked amplification of the detector signal enhances the precision and temporal resolution of the CSD. Oversampling of the detector signal at 10 Hz permits subsequent data retrieval to be adapted to changing ambient levels by either enhancing signal to noise when sulfur dioxide levels are low or by maximizing temporal resolution of derived data when levels are high. he instrument has advantages over existing instruments based on Chromatographie separation in that the CSD provides accurate and reliable measurements at low parts per trillion by volume sulfur dioxide with high time resolution. The CSD is compact and automated and does not require cryogenic materials, making this instrument suitable for remote field locations. The high temporal resolution, specificity for SO2, and sensitivity of the CSD make it a good candidate for installation on an aircraft. Airborne studies of SO2 with a sensitive, fast time response instrument may offer new insight into the understanding of phenomena such as gas-to-particle conversion, long-range transport of pollutants, and the oxidation of biogenically produced sulfur gases.