Abstract. An understanding of gas-phase HNO3 transmission through an inlet is necessary to evaluate the quality of NOy measurements from an aircraft platform. A simple, inexpensive, low-volume Teflon inlet is described and its suitability as an aircraft inlet for gas-phase NOy is assessed. Aerosol transmission is not characterized, but inlet design and orientation probably discriminates against the majority of aerosol by mass. Laboratory data, in-flight HNO3 standard addition calibrations, and ambient NOy measurements from the 1997 North Atlantic Regional Experiment aircraft mission are used to characterize inlet transmission efficiencies and time constants. Laboratory tests show high transmission efficiencies for HNO3 which are relatively independent of ambient temperature and humidity. In-flight standard addition calibrations were carried out at ambient temperatures ranging from -20 ø to +8øC and relative humidities from 3% to 71%. These data suggest that nearly all the sampled air contacts an inlet surface, with 90% of added HNO3 being transmitted in -1.5 s. Ambient data are presented to demonstrate negligible hysteresis in 1-Hz NOy measurements, relative to variability observed in ozone data, from an air mass where HNO3 is expected to be a large fraction of the total NOy. Power spectra of ambient NOy (at temperatures from -35 ø to +35øC and relative humidities from 3% to 100%) and ozone measurements suggest an effective NOy instrument time constant of-2 s.

Abstract. An aircraft-based instrument for the measurement of peroxyacetic nitric anhydride (PAN) and related compounds peroxypropionic nitric anhydride (PPN), and peroxymethacrylic nitric anhydride (MPAN) is described. The instrument functions by direct injection of a small sample (2 ambient cm3) into a wide bore fused silica capillary gas chromatographic separation column with subsequent detection by electron capture. The efficiency of separation and early elution of water made possible a sampling frequency of once every 5 min. The selective destruction of PAN type compounds at 125øC in actual ambient samples showed that no interfering species were present. Calibration of the instrument was accomplished by the total oddnitrogen (NOy) measurement of air mixtures of high-purity PANs. Inflight calibrations of PAN in either thermally decomposed ambient air or dry zero air showed that the sensitivity of the instrument to PAN was not affected by other matrix species such as carbon dioxide or water. The instrument response to PPN and MPAN relative to that of PAN was consistent (within 5%) over the span of several months. The instrument response to PAN was linear up to 3.5 ppbv and the slope of the response versus [PAN] indicated a relative standard deviation of 2% over the course of a 30-day field study. The detection limits of the method for PAN and PPN were estimated to be 5 pptv (3s) based on the uncertainty of peak detection. The overall accuracy of the PAN measurement was estimated to be +_(5 pptv+15%) in one campaign and +_(5 pptv+20%) in others.

Abstract. The potential impact of ship emissions on concentrations of nitrogen oxides and reactive nitrogen compounds in the marine boundary layer is assessed using a global chemical transport model. The model predicts significant enhancements of these compounds over large regions, especially over the northern midlatitude oceans. This resuit is consistent with a recently published study, though the impacts predicted here are more widespread and the peak enhancements are not as large. However, comparisons of model results with recent measurements over the central North Atlantic Ocean do not provide support for these model predictions. While one cannot completely overlook the possibility that emissions of nitrogen oxides from ships may be overestimated, our analysis suggests that there may be a gap in our understanding of the chemical evolution of ship plumes as they mix into the background atmosphere in the marine boundary layer. On a related note, it is also possible that the overestimate of the impacts of ships on nitrogen oxides in the marine boundary layer by global models is due to the lack of parameterized representations of plume dynamics and chemistry in these models.

Abstract. Vertical profiles of ozone mixing ratio, water vapor mixing ratio, and temperature obtained during August 3-13, 1995, at Ferryland Downs, Newfoundland, Canada, as part of the North Atlantic Regional Experiment (NARE) demonstrate the use of high-altitude tethered balloons and kites as measurement platforms. In combination with a novel, fast winching system, previously developed for use with kites, tethered balloons were used for profiling chemical species and meteorological parameters to altitudes as high as 7.6 km. Tethered balloon profiling complements profiling with kite systems by expanding the range of wind conditions over which data can be obtained. A total of 65 profiles were collected using these platforms. Elevated ozone mixing ratios highly anticorrelated with water vapor mixing ratios observed during August 4-7 suggest an upper atmospheric source for ozone-rich air during summertime in the Maritime Provinces of Canada. Ozone mixing ratios reaching 100 parts per billion by volume (ppbv) in this air mass were associated with water vapor mixing ratios as low as 0.1 g kg-1. Profiles collected during August 11-13 demonstrate the use of kite and balloon systems to obtain vertical profiles over a wide range of wind conditions. Ozone mixing ratios of 65 ppbv were observed at 1 km altitude on August 12, while profiles collected on August 13 exhibit no evidence of elevated ozone. These results document the rapid transport of an air mass containing elevated ozone levels over the sampling site that would not have been possible with either system alone.

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