MEASUREMENTS OF THE CHEMICAL-COMPOSITION OF STRATIFORM CLOUDS

Measurements are reported of the chemical composition of the liquid water and interstitial air in water ( greater than 0 degree C), non-precipitating stratus and strato-cumulus clouds at various locations in the eastern United States. Inorganic ionic composition of the cloudwater was generally dominated by H** plus , NH//4** plus , NO//3** minus and SO//4**2** minus , similar to the composition of precipitation in this region of the U. S. Concentrations of the corresponding interstitial aerosol species and gaseous HNO//3 were invariably low in comparison to concentrations of the respective ionic species in cloudwater. In contrast, the concentration of NO//x (i. e. NO plus NO//2 plus organic nitrates) was invariably comparable to or in excess of that of cloudwater nitrate. Sulfur dioxide was found at varying concentrations relative to cloudwater sulfate. In many cases, the SO//2 concentration was quite low ( less than 0. 2 ppb) even in the presence of substantial quantities of cloudwater SO//4**2** minus ( greater than 1 ppb equivalent gas-phase concentration), suggesting large fractional conversion and incorporation into cloudwater. In other cases, in which dilute SO//2 plumes (p(SO//2) greater than 5 ppb) were observed in the cloud interstitial air, the gaseous SO//2 concentration substantially exceeded the cloudwater sulfate concentration.