Grantee Research Project Results
1998 Progress Report: An Investigation Into HONO Formation Mechanisms in the Troposphere
EPA Grant Number: R826182Title: An Investigation Into HONO Formation Mechanisms in the Troposphere
Investigators: Zhou, Xianliang
Institution: New York State Department of Health
EPA Project Officer: Hahn, Intaek
Project Period: December 1, 1997 through November 30, 1999 (Extended to November 30, 2000)
Project Period Covered by this Report: December 1, 1997 through November 30, 1998
Project Amount: $162,728
RFA: Exploratory Research - Environmental Chemistry (1997) RFA Text | Recipients Lists
Research Category: Water , Air , Safer Chemicals , Land and Waste Management
Objective:
The proposed research is to investigate reactions leading to nitrous acid (HONO in gas phase and HNO2 in liquid phase) formation, and thus to provide insight into the mechanisms for HONO formation in the troposphere under both NOx -rich and NOx -limiting conditions. Two types of reactions are to be investigated in the project, i.e., nitric acid reduction by various reducing agents in liquid phase and NO/NO2H2O reactions in solutions and on various surfaces.Progress Summary:
Reduction of HNO3 by formaldehyde (HCHO), sulfur dioxide (SO2) and bromide (Br-), as a HONO source has been investigated in laboratory. The results are summarized as follows:
- At low acidity, i.e., in ~mM levels of H2SO4 reaction media, the reduction of HNO3 by HCHO and Br- was found too slow for any HNO2 production to be detected in laboratory. The HNO2 production rate was < 10-8 M/hr at mM reactant concentrations and ~10 µM initial HONO concentration. Therefore the HNO3 reduction by HCHO and Br- in cloud/fog water is not a significant HONO source in the atmosphere.
- At higher H2SO4 concentrations between 0.5-8 M, the reaction of HNO3-HCHO was first-order to HCHO and HNO2, 1.3th-order to acidity of sulfuric acid (i.e., Fammett Function, Ho), but showed little dependence on HNO3 concentration with H2SO4 concentration $ 2.5 M. In liquid H2SO4 aerosols containing 75% H2SO4, the HNO2 production rate was estimated to be ~10-4 M/hr. Therefore, the reduction of HNO3 by HCHO may be a significant HONO source in the upper troposphere.
- SO2 was found to be an effective reducing agent for HNO2, especially at high acidity. Therefore, the presence of SO2 in cloud/fog waters and liquid aerosols may act as a sink rather than a source for atmospheric HONO.
- HNO2 production was observed in the HNO3 reduction by Br- in strong acidic solutions. This reaction is still under investigation in the laboratory.
Future Activities:
Research activities will be focused on HNO3-Br- reaction in H2SO4 media during the first 2 months, and then on NO/NO2H2O reactions in bulk solutions and on surfaces in the following 12 months.Journal Articles:
No journal articles submitted with this report: View all 3 publications for this projectSupplemental Keywords:
Nitrous acid, nitric acid, HNO3-HCHO reaction, HNO3-SO2 reaction, HNO3-Br- reaction, HONO source., Air, Scientific Discipline, Chemistry, Environmental Chemistry, Engineering, Chemistry, & Physics, gas-liquid reactor, photooxidants, HONO, chemical composition, troposphere, reaction kinetics, chemical kinetics, ozone, nitrous acid formationProgress and Final Reports:
Original AbstractThe perspectives, information and conclusions conveyed in research project abstracts, progress reports, final reports, journal abstracts and journal publications convey the viewpoints of the principal investigator and may not represent the views and policies of ORD and EPA. Conclusions drawn by the principal investigators have not been reviewed by the Agency.