Collaborative Research: An Investigation into Daytime HONO Chemistry in the Marine Boundary Layer

University Of South Florida, Tampa FL

Investigators

Abstract

The amount of reactive nitrogen in the gas phase has a significant impact on the oxidative capacity of the atmosphere. In the terrestrial boundary layer (TBL), gas phase nitrous acid (HONO) is produced by various mechanisms from reactions of precursors like nitrogen oxides (NOx) and nitric acid (HNO3) on surfaces. These processes, which recycle deposited HNO3 to photochemically reactive nitrogen species, such as HONO, are often called "renoxification." In the marine boundary layer (MBL), ocean waves produce sea salt aerosols that are highly enriched in organic matter and nitrate. These particles may serve as reactive media for photochemical and heterogeneous reactions leading to HONO formation. However, the distribution and the chemistry of HONO in marine environments are not well understood, with only a few field measurements of HONO reported in the MBL to date. This project aims to investigate renoxification resulting from rapid photolysis of particulate nitrate associated with sea-salt aerosol as a source of HONO. Work includes a series of field measurements, laboratory experiments and model simulations. Specifically, researchers will: 1) Conduct measurements at Tudor Hill Marine Atmospheric Observatory in Bermuda and establish the temporal distribution of HONO in the MBL in spring and late summer of 2019. Work will include collecting meteorological parameters and measurements of pNO3, HNO3, NOx, aerosol loading, aerosol ionic components (NO3-, Cl-, SO42-, Na+, Mg2+, and Ca2+), O3, and VOCs. 2) Collect aerosol samples and use them to conduct photochemical experiments in the laboratory for the determination of the photolysis rate constant of pNO3 leading to HONO and NO2 productions. 3) Conduct box and 3D chemical transport model simulations to examine pNO3 photolysis as a HONO source and as a renoxification pathway, and to evaluate the role of this process in oxidant production in the MBL. This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.