The objective is to detect field evidence for reaction pathways of nitrogen oxides in clouds and the quantification of reaction rate coefficients.
Field experiments have shown that the major source of nitrate formation as an airstream passes through a cap cloud is from the solution of N2O5 formed from the gas phase oxidation of NOx with ozone, in agreement with the known NOy chemistry. The measurements of NOy species indicate that a significant fraction (up to a quarter) may be due to the presence of bifunctional organic nitrates derived from night-time oxidation of alkenes initiated by the NO3 radical.
The field experiments are conducted on Great Dunn Fell in the United Kingdom. A wide range of measurements is made at the 3 ground based sites on Great Dunn Fell, upwind, at the summit and downwind, in combination with measurements from aircraft sampling.

Measurements will be made of hydrogen peroxide in air and cloud water to extend knowledge of the behaviour of this important oxidant for cloud chemistry. These measurements together with those of the nitrogen oxides species will provide useful information on the basic mechanisms forming hydrogen peroxide in the background atmosphere.

The wet and dry deposition rates of the nitrogen oxides to the hillside will also be measured using a combination of the eddy correlation and gradient techniques.

After all these measurements modelling and interpretation of data will be performed.