Heterogeneous chemistry in the troposphere: Experimental approaches and applications to the chemistry of sea salt particles

David O De Haan,Theo Brauers,Kawon Oum,Jochen Stutz,Trent Nordmeyer,Barbara J Finlayson-Pitts

doi:10.1080/014423599229910

Abstract

Halogen atoms, particularly chlorine atoms, are well known to be highly reactive and to play a central role in the chemistry of the upper atmosphere. A large potential source of these halogens in the lower atmosphere (troposphere) exists in the form of sea salt particles. A variety of laboratory, field and modelling studies strongly suggests that there are heterogeneous reactions of sea salt particles which generate photochemically active halogen species such as Cl in marine areas. In addition, there is increasing evidence for a contribution of bromine atoms to tropospheric chemistry in marine regions at high latitudes. We review here briefly the potential importance of such halogen reactions and evidence for their role in the chemistry of the troposphere. Studies carried out in this laboratory to elucidate, at a molecular level, the mechanisms of reaction of synthetic sea salt and its components with gases of tropospheric interest are reviewed. Initial results obtained using a new aerosol apparatus recently constructed in this laboratory to study the reactions of aerosol particles above and below the deliquescence point of the salts are also discussed.

Highlights

It has been recognized for many decades that gas, liquid and solid phases all play a role in atmospheric chemistry (Leighton 1961, Andreae and Crutzen 1997, Finlayson-Pitts and Pitts 1997, Ravishankara 1997)
We describe a variety of experimental approaches, including a new aerosol chamber recently constructed in this laboratory which was designed to study such gas± particle interactions under conditions simulating those found in the troposphere
We review here briey the results of Knudsen cell studies which allow determination of the reaction probability and provide key insights into the mechanism, and in particular the controlling role of surface-adsorbed water (SAW) in the uptake and reaction of HNO$

Summary

Introduction

It has been recognized for many decades that gas, liquid and solid phases all play a role in atmospheric chemistry (Leighton 1961, Andreae and Crutzen 1997, Finlayson-Pitts and Pitts 1997, Ravishankara 1997). Given the small concentrations of N# O% which will coexist with NO# at the sub-parts per million concentrations found in ambient air even in polluted regions, it is unlikely that this reaction of NO# ± N# O% will be important in the troposphere Subsequent studies in this and other laboratories (Finlayson-Pitts et al 1989a, Behnke and Zetzsch 1989a, b, 1990, Behnke et al 1991, 1992, 1993a, b, 1994, 1995, 1997, Livingston and Finlayson-Pitts 1991, Junkermann and Ibusuki 1992, Zetzsch and Behnke 1992, 1993, Niki and Becker 1993, George et al 1994, Msibi et al 1994, Timonen et al 1994, Vogt and Finlayson-Pitts 1994a, b, 1995a, Caloz et al 1996, Fenter et al 1996, Schweitzer et al 1998) established that, in addition to the HNO$ and NO# reactions, there were additional processes involving other oxides of nitrogen which could generate photochemically active compounds, for example. We discuss in the remainder of this article some studies carried out in this laboratory directed to this question

Formation of unique surface nitrate species

Findings

Conclusions