This grant provides for four lines of research: (1) The testing of independent calibration methods to broaden the application of a free radical detector (the PERCA; see below) to a wider range of hydrocarbon peroxy radicals, along with improvements in the detector itself; (2) the further optimization of an existing fast ozone monitor for eddy correlation measurements; (3) the development of a gas chromatograph for measuring atmospheric nitrogen dioxide and PAN (peroxyacetyl nitrate); (4) the development of systems for measuring the response of molecular species to exposure to light ("j values"). PERCA is the acronym for a "peroxy radical detector using chemical amplification." The principal object of measurement is the transient chemical species formed by the attachment of a hydrogen atom to an oxygen molecule (formula: H0 ). Under 2 atmospheric conditions these molecules are constantly being produced in the presence of sunlight, and also constantly being destroyed in chemical reactions. A minute concentration may be sustained, however, sufficient to confer on H0 an important 2 role in oxidizing other trace species, e.g., nitric oxide (NO). It is therefore important to be able to measure these low levels of HO and of its hydrocarbon-derived analogues in order to 2 construct valid mathematical representations of the total atmospheric chemical system. The PERCA is now operational, but further calibration studies are needed in order to extend its use to a wider range of peroxy radicals. A fast ozone monitor is now operational, but the proposed optimization is directed to the development of a simpler device of lighter weight better adapted to aircraft measurements of upward or downward fluxes of ozone through the atmosphere. The PAN/NO chromatograph is a device for field measurement of 2 these nitrogen compounds. PAN is a "reservoir" species for active nitrogen in the atmosphere and it has deleterious biological properties. Nitrogen dioxide is a principal carrier of light energy in atmospheric photochemical systems. The system for measuring "j values" will find use in correlating the progress of atmospheric photochemical changes with the driving force of variable light intensity.
