Paul Kelley

Composition of the troposphere over the Indian Ocean during the monsoonal transition

The atmosphere over the equatorial Indian Ocean is a unique environment in which to study the chemical and radiative effects of an intense source of anthropogenic emissions from the northern hemisphere directly coupled to the relatively pristine background conditions present in the southern hemisphere. As an initial investigation into the role of the intertropical convergence zone (ITCZ) on interhemispheric transport of pollutants, a number of trace atmospheric species were measured aboard the National Oceanic and Atmospheric Administration (NOAA) R/V Mal- colm Baldrige between Durban, South Africa, and Colombo, Sri Lanka, from March 12 to April 22, 1995. Sharp increases in the concentrations of carbon monoxide (CO), carbon dioxide (CO2), and aerosols were associated with four distinct meteorological regimes transected by the cruise track from 33oS to 9oN. Across the ITCZ, aerosol concentrations, including non-sea-salt sulfate, nitrate and ammonium, increased by a factor of 4. Surface ozone measurements showed a latitu- dinal gradient with a minimum near the equator and a strong diurnal variation in the equatorial re- gions. The latitudinal profile of gas-phase reactive nitrogen paralleled ozone and was higher in the remote southern hemisphere than in the remote northern hemisphere. Evidence of direct anthro- pogenic impact on the region was observed more than 1500 km from the southern tip of India. Back trajectories, calculated with NOAAs medium range forecast data using the Hybrid Single- Particle Lagrangian Integrated Trajectory (HY-SPLIT) program, identified the origin of the air mass regimes characterized by the trace gas and aerosol data. Continental emissions in the north- ern hemisphere were shown to have a major impact on the radiative properties and oxidizing capac- ity of the marine atmosphere.

Large‐scale pollution of the atmosphere over the remote Atlantic Ocean: Evidence from Bermuda

Ozone acts as a greenhouse gas and controls much of the oxidizing capacity of the atmosphere. Photochemical production of ozone in urban areas (smog) is a serious environmental problem, but how far this process extends on regional or global scales remains a major unanswered question in atmospheric science. In summer, Bermuda basks in pristine marine air, but in spring, episodes of high ozone are common. From meteorological analyses and observation of ozone, carbon monoxide, and reactive nitrogen compounds, the authors conclude that half or more of the excess ozone in Bermuda originates from air pollution over eastern North America. 50 refs., 7 figs., 2 tabs.

Rate of NO2 photolysis from the surface to 7.6 km altitude in clear‐sky and clouds

The photolysis of NO2 by solar UV radiation produces ozone in the troposphere. Radiative transfer models predict an increase in actinic UV flux with altitude, but this has never been well documented experimentally. This paper presents direct airborne measurements of both upwelling and downwelling flux (2π sr each) from 0.2 to 7.6 km for clear-sky conditions and 58° solar zenith angle. The downwelling flux increases by 33% and upwelling flux increases by a factor of four going from the surface to 7.6 km. Excellent agreement was found with models using detailed solutions to the radiative transfer equation or the six-stream approximation, while a number of two-stream computer models agreed within 10 to 25%. Compared to clear-sky measurements, in-cloud enhancement of up to 58% was also observed.

Modification of a commercial cavity ring-down spectroscopy NO2 detector for enhanced sensitivity

Nitrogen dioxide (NO(2)) plays a central role in atmospheric chemistry, air pollution, and biogeochemical cycles. Many analytical techniques have been developed to detect NO(2), but only chemiluminescence-based instruments are commonly, commercially available. There remains a need for a fast, light, and simple method to directly measure NO(2). In this work we describe the modification and characterization of a small, commercially available cavity ring-down spectroscopy (CRDS) NO(2) detector suitable for surface and aircraft monitoring. A metal oxide scrubber was added to remove NO(2), and provide a chemical zero, improving the detection limit (3sigma of the background noise) from several parts per billion by volume (ppbv) to 0.06 ppbv, integrated over 60 s. Known interferences by water and particles were removed using Nafion tubing and a 1 microm Teflon filter, respectively. A 95% response time of 18+/-1 s was observed for a step change in concentration. The CRDS detector was run in parallel to an ozone chemiluminescence device with photolytic conversion of NO(2) to NO. The two instruments measured ambient air in suburban Maryland. A least-squares fit to the comparison data resulted a slope of 0.960+/-0.002 and R of 0.995, showing agreement within experimental uncertainty.