Chebogue Point Research Articles

Meteorological mechanisms for transporting O3 over the western North Atlantic Ocean: A case study for August 24–29, 1993

A large‐scale view of O3 transport over the western North Atlantic Ocean (WNAO) in summer illustrates distinct sources of O3, and separate transport mechanisms are important at different vertical levels in the troposphere. The week‐long period presented covers a sequence of O3 sondes released from Bermuda and encompasses two surface O3 events in the month‐long NARE intensive. O3 and CO peaked at Chebogue Point on the evening of August 25 and after midnight on the morning of August 28. At Sable Island, peaks occurred during early morning of August 26 and late morning of August 28. These events occurred under W‐SW winds associated with advancing low‐pressure systems that transported anthropogenic pollutants over the WNAO. The concentrations dropped with the passage of a trough or a cold front. Evidence suggests the surface was occasionally isolated from polluted air during favorable transport with pollutants lifted in warm sector flow riding over a wedge of cool, thermodynamically stable air. In addition to surface O3, the O3‐sonde profile over Bermuda on the morning of August 27 showed a deep layer of O3 from 6 to 12 km. Using back trajectories and two tracers (isentropic potential vorticity and water vapor), we illustrate that stratospheric ozone exchanged into the upper troposphere in conjunction with surface cyclogenesis was advected through the middle to upper troposphere over the midlatitudes with the potential to reach lower altitudes through subsidence in regions of anticyclonic motion.

Concentrations of carbonyl compounds and the carbon isotopy of formaldehyde at a coastal site in Nova Scotia during the NARE summer intensive

The concentrations of gaseous atmospheric carbonyl compounds have been measured at a coastal site on the southern tip of Nova Scotia during August 1993 as part of the National Oceanic and Atmospheric Administration's North Atlantic Regional Experiment (NARE) summer intensive. The DNPH‐cartridge technique was used for sampling, with analysis by HPLC with UV absorbance detection. The carbon isotopic content of formaldehyde was measured using a novel collection technique on bisulfite‐coated filters followed by accelerator mass spectrometric determination of 14C content and 13C/12C isotopic ratios. Results from this study indicate that quantifiable levels above about 100 parts per trillion by volume were found at the Chebogue Point, Nova Scotia, site for several carbonyls, formaldehyde, acetaldehyde, acetone, propionaldehyde, methyl ethyl ketone, and benzaldehyde, for most 6‐hour sampling periods. Six‐hour averaged formaldehyde levels of <0.5 to about 3.5 parts per billion were found during periods of local influence and during influence of continental air masses crossing eastern Canada and northeastern US. In contrast, background levels of formaldehyde of 200–400 pptv were found under conditions of predominantly marine back trajectories. Large fractions of contemporary carbon (of the order of 80%) were found in collected formaldehyde samples for all transport regimes and formaldehyde concentrations, suggesting that biogenic sources of hydrocarbon precursors to formaldehyde predominated during the summer season.

Comparison of Wind Profiler and Aircraft Wind Measurements at Chebogue Point, Nova Scotia

Abstract In August 1993, a 915-MHz boundary layer wind-profiling radar was deployed at Chebogue Point, Nova Scotia, to provide wind, turbulence, and boundary layer structure information for the North Atlantic Regional Experiment summer 1993 intensive campaign. The National Research Council Canada Twin Otter atmospheric research aircraft was also part of that campaign. During the campaign, the Twin Otter flew 29 soundings over Chebogue Point. This paper describes a comparison of the wind speed and direction measured by the profiler and the aircraft. In the height range 300–2000 m above sea level, the random difference between the wind speed measurements is 0.9 m s−1, and the random difference between the wind direction measurements is 9°. There is a small systematic difference in the wind speeds (0.14 m s−1) that is probably due to uncertainty in the zenith angles of the radar beams and extremely good agreement (within 0.5°) in the wind direction. The Kalman filter-smoother technique used to remove drifts ...