TO ELUCIDATE THE REACTION MECHANISMS FOR THE FORMATION OF HNO3, PAN AND OTHER AIR POLLUTANTS.
The reaction pathways and related physicochemical properties of the nitrogen oxides and their secondary reaction in the troposphere were studied.
Nitrous acid has been detected in polluted atmosphere during the night. Its photolysis provides an important early morning source of hydroxyl radicals in strongly polluted ozone depleted air masses.
The gamma coefficient of nitrous acid on water was measured. The sticking, or mass accommodation coefficient, is an expression for the fraction of the molecules that is successfully scavenged by droplets after the occurrence of molecule droplet collisions.
For nitrous acid the equilibrium between the droplet phase and interstitial air of clouds and fogs is rapidly established, the relaxation being exclusively controlled by diffusion in the gas and liquid phases. The gamma coefficients for nitric acid and nitrogen oxide (N2O5) indicated that absorption of these species by cloud or fog droplets will not be limited by surface resistance, but by diffusion in the gas and liquids phases, as for nitrous acid.
Solubility studies showed that alkyl mononitrates were weakly soluble and stable in aqueous solution, their atmospheric lifetimes unaffected by the liquid water content of the atmosphere. The lifetime of peroxyacetylnitrate (PAN) was also unaffected by clouds, fog, wetted aerosols, and rain.
In contrast, hydroxy nitrates, nitroxy acetone and, alkyl dinitrates were 2 to 4 orders of magnitude more soluble in water than the mononitrates, the lifetimes thus affected by rain and washout.
The partitioning from the nitrogen dioxide conversion between nitric acid and phytotoxic products was investigated in smog chamber experiments. The experiments involved the photolysis of nitrogen dioxide in purified air, in the presence of 5 prototype hydrocarbons. The nitric acid yield was found to be inversely dependent on the PAN forming potential of the hydrocarbon under study. The concentration time profiles of the reactants and product s compare favourably with model calculations.
THE RESEARCH PROJECT COMPRISES A SMOG CHAMBER STUDY TO BE CARRIED OUT AT THE UNIVERSITY OF PATRAS (PROPOSAL 448) AND INVESTIGATIONS ON ELEMENTARY REACTIONS AS WELL AS HETEROGENEOUS UPTAKE OF NO CONVERSION PRODUCTS TO BE CARRIED OUT AT THE UNIVERSITY OF BONN (PROPOSAL 31).
IN THE SMOG CHAMBER EXPERIMENTS THE POTENTIAL TO FORM HNO3 AND PAN IS STUDIED UNDER VARIOUS HYDROCARBON /NOX CONCENTRATION RATIOS, WHILE THE ELEMENTARY REACTIONS OF NO2 AND OZONE STUDIED IN BONN CAN PROVIDE THE KINETIC DATA TO BE USED FOR THE INTERPRETATION OF THE SMOG CHAMBER EXPERIMENTS.
PROP. 448 S. GLAVAS, PATRAS
Funding SchemeCSC - Cost-sharing contracts