Investigation of the Photochemistry of Ammonia Adsorbed to Titania Surfaces as a Source of Oxides of Nitrogen in the Atmosphere
EMSL Project ID
46905
Abstract
Field measurements consistently show that photolysis of nitrous acid (HONO) is by far the most important source of OH radicals in the early morning hours, more so than OH generated from ozone and formaldehyde photolysis, and is essential for initiating the free radical chemistry that leads to ozone and particle formation in polluted urban areas. Despite this, atmospheric chemistry models under-predict the tropospheric concentrations of HONO (and hence OH radical) that are measured. Chemical mechanisms that involve photocatalytic reactions of NH3 on mineral dust and boundary layer surfaces containing TiO2 may explain the high levels of HONO measured in urban environments, but they remain poorly understood. This is a potentially widespread phenomenon since ammonia is ubiquitous in the environment and TiO2 is a natural component of mineral dust (0.1-10% by mass, depending on the source) and is present in glass and building materials. The goal of this research is to obtain molecular-level insights into the role that TiO2 plays in converting reactive nitrogen species into HONO and NO2 at atmospheric interfaces. To do this we will study the product distribution and kinetics of the photooxidation of NH3 on titania surfaces under atmospheric conditions (e.g., in the presence of water and air) using a combined FTIR and mass spectrometric system available at PNNL. In addition, isotopic substitution will be used to reveal mechanistic insights and help identify reaction intermediates and products based on comparison of the peak positions for labeled and non-labeled species.
Project Details
Project type
Limited Scope
Start Date
2012-03-07
End Date
2012-05-07
Status
Closed
Released Data Link
Team
Principal Investigator