NITROCAT: Nitrous acid and its influence on the oxidation capacity of the atmosphere

• Research unit: EU RFP
• Project number: 99.0042-2

Key words (English)

Photosmog; HONO; diesel exhaust; VOC; heterogeneous chemistry; ozone

Alternative project number (English)

EU project number: EVK2-1999-00025

Research programs (English)

EU-programme: 5. Frame Research Programme - 1.4a.2 Global change, climate and biodiversity

Short description (English)

See abstract

Further information (English)

Full name of research-institution/enterprise:
Paul Scherrer Institut PSI

Laboratory of Radio and Environmental Chemistry

Partners and International Organizations (English)

Coordinator: Bergische Universität, Wuppertal (D)

Abstract (English)

Nitrous acid (HONO) seems to be an important precursor of OH radicals due to its photolysis in sunlight. The sources of HONO in the atmosphere are still not sufficiently understood. Therefore, within the project NITROCAT, HONO formation and its impact on ozone formation has beem investigated by a combined effort of laboratory, field and modeling studies. The Paul Scherrer Institue (PSI) has contributed by investigating heterogeneous reactions on condensed organic species associated with the ambient aerosol or other surfaces. Up to now, the heterogeneous reaction of NO2 with adsorbed water on mineral surfaces as well as the reaction of NO2 with soot surfaces had been investigated. However, both reactions turned out to be not significant sources for secondary HONO formation in the atmosphere.
During the first year, we concentrated on the reactivity of semi-volatile organic compounds that are emitted in diesel exhaust. We were able to show that the exhaust contains polar organic compounds which are in the gas-phase when the exhaust is emitted into the atmosphere but which condense onto humid or aqueous surfaces at room temperature. In surface adsorbed water or within a bulk liquid phase these species react with dissolved NO2 to form nitrite, which can be released as HONO if the aqueous phase is sufficiently acidic. The actual chemical identity of the reactive compounds responsible for the NO2 to nitrite conversion could not be identified in this complex system.
One class of compounds already known to have this ability were partially oxidized aromatic compounds. During the second year, we therefore concentrated on investigating the aqueous phase reaction of NO2 with resorcinol. Resorcinol in the atmosphere can either form part of combustion exhaust, but can also be formed though photo-oxidation of aromatic precursors. The experiments showed that NO2 reacts with resorcinol either on a solid surface or within the aqueous phase to form HONO and nitrite, respectively. For the aqueous phase case, the detailed pH dependent kinetics of this one-electron reduction process was investigated. This delivered kinetic constants to be incorporated in multi-phase atmospheric chemistry models.

References in databases (English)

Swiss Database: Euro-DB of the
State Secretariat for Education and Research
Hallwylstrasse 4
CH-3003 Berne, Switzerland
Tel. [phone]
Swiss Project-Number: 99.0042-2