O O

FIGURE 5.24 Schematic of bubble apparatus (adapted from Shorter et al., 1995).

Trace gas Carrier gas

FIGURE 5.24 Schematic of bubble apparatus (adapted from Shorter et al., 1995).

6. Aerosol Chambers

Several aerosol chambers have been applied recently to studying aerosol kinetics and mechanisms. Figure 5.25 shows one type of design that is a variant on flow tubes used extensively in studying gas-phase reactions. The aerosol travels along the length of a laminar flow reactor, with gases added through a movable injector, and changes in the gas and/or particles are followed as a function of reaction time, typically of the order of seconds. As a result, these have been applied to studying fairly fast heterogeneous reactions (e.g., see Fried et al., 1994; and Lovejoy and Hanson, 1995). Alternate designs used to study slower reactions on time scales of the order of minutes have also been implemented (e.g., see Karlsson and Ljungström, 1995).

Static aerosol chambers have been developed for studying slower heterogeneous reactions (e.g., Zetzsch and Behnke, 1992; Anthony et al., 1995; De Haan et al., 1999). Figures 5.26 and 5.27 show one such system (De Haan et al., 1999). It consists of a 561-L stainless steel

Gas inlet

Aerosol -

Gas inlet

Movable injector

To gas detector and particle counter

Movable injector

To gas detector and particle counter

FIGURE 5.25 Schematic diagram of aerosol apparatus (adapted from Fried et al, 1994).

and aluminum chamber whose walls are coated with halocarbon wax to provide a relatively unreactive surface. The top has a series of windows that can be either quartz or borosilicate glass, so that photolysis of the gas-particle mixtures can be studied. The chamber can be heated and pumped. It is equipped with two long-path optical systems, one in the UV-visible (for differential optical absorption spectrometry, DOAS) and one for FTIR (see Chapter If.A.lc). An atmospheric pressure ionization mass spectrometer (API-MS) is also interfaced to the chamber to measure gases such as Cl2 and Br2, which cannot be measured using DOAS or FTIR. An aerosol generator and differential mobility analyzer are attached for generating particles and determining their size distribution (see Chapter ll.B.2b). This has been applied, for example, to studies of Cl2 generation from the photolysis of 03 in the presence of deliquesced sea salt particles (Oum et al., 1998).

7. Liquid Jet Apparatus

Figure 5.28 shows a liquid jet apparatus used to study the uptake of HONO on water (Bongartz et al., 1994). Water is forced through a capillary to form a jet with a diameter of the order of fOO ¡xm. The jet flows

FIGURE 5.26 Schematic diagram of side view of an aerosol apparatus (see De Haan et al., 1999, for a description of the chamber).

DO AS FTIR

( Detector}

] ZnSe window

High V

] ZnSe window

High V

Reactants

FIGURE 5.27 Top view of aerosol apparatus (De Haan et al., 1999).

( Detector}

Q3 scan

Q1 scan
0 0

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