Application of an improved method for measurements of gaseous nitric acid in the nonurban atmosphere

A modified filter technique to separate particles and gaseous HNO3 is described, which is based on the use of filters of the Millipore FPLG type in combination with a virtual impactor. It enables routine measurements of gaseous HNO3 in the atmosphere at background levels. Some results of measurements both in the marine background and over rural and semi-rural continental regions are presented.