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OZONE SENSOR

Ozone chemistry in the Arctic is of interest due to the importance of ozone as an oxidizing agent, and because it undergoes near complete depletion events in early spring.  These ozone depletion events (ODEs) were first observed in the mid-eighties by Bottenheim et al.  Since then, people have been trying to understand how they happen, why they happen, and how they influence other important chemical reactions in the region.  It is believed that these ODEs are a product of a catalytic bromine cycle that can only happen under special conditions (e.g. low temperature, presence of sunlight, large bromine source, and ice/aerosol surface upon which to regenerate the chain precursors).  Bromine comes from sea salt, which is readily available at the Arctic coastal sites where ODEs are observed.  However, how the bromide converts to Br2 and BrCl, and subsequently reacts with ozone, is slightly less well understood.  The current mechanism involves the bromide ion reacting with ozone, or a BrCl molecule (rxns 1-2; both of which are relatively slow). In an appropriately acidic solution (1) can go on to form the hypohalous acid and eventually molecular bromine (3), which can then photolyze to bromine radical and react with ozone (4, yields a Br radical which has a much faster rate constant for the ozone reaction than does Br-).  The monoxide will then self react to form molecular oxygen and bromine (5).  Since reaction 3 involves one Br atom in the gas phase (HOBr) reacting with a surface to produce two reactive bromine atoms (Br2), this is called the bromine explosion.A significant aspect of our current work is to measure the ozone mixing ratios in the Arctic as a function of time of year, and compare this data with other atmospherically relevant species (e.g. BrO).  The ozone measurement is done by a specialized 2B Technologies model 205 instrument (Figure 1).  This is a dual beam instrument that detects ozone in one cell while using the other cell as a blank.  The method of detection is absorbance of light (254 nm) emitted from a low pressure mercury lamp (Figure 2).  Some of the requirements for our research to be successful were for the instrument to have low power consumption, and to be stable over a wide range of temperatures.  The 2B instruments were found to be ideal in this respect as can be seen in Figures 3-4.

Ozone chemistry in the Arctic is of interest due to the importance of ozone as an oxidizing agent, and because it undergoes near complete depletion events in early spring.  These ozone depletion events (ODEs) were first observed in the mid-eighties by Bottenheim et al.  Since then, people have been trying to understand how they happen, why they happen, and how they influence other important chemical reactions in the region.  It is believed that these ODEs are a product of a catalytic bromine cycle that can only happen under special conditions (e.g. low temperature, presence of sunlight, large bromine source, and ice/aerosol surface upon which to regenerate the chain precursors).  Bromine comes from sea salt, which is readily available at the Arctic coastal sites where ODEs are observed.  However, how the bromide converts to Br2 and BrCl, and subsequently reacts with ozone, is slightly less well understood.  The current mechanism involves the bromide ion reacting with ozone, or a BrCl molecule (rxns 1-2; both of which are relatively slow). In an appropriately acidic solution (1) can go on to form the hypohalous acid and eventually molecular bromine (3), which can then photolyze to bromine radical and react with ozone (4, yields a Br radical which has a much faster rate constant for the ozone reaction than does Br-).  The monoxide will then self react to form molecular oxygen and bromine (5).  Since reaction 3 involves one Br atom in the gas phase (HOBr) reacting with a surface to produce two reactive bromine atoms (Br2), this is called the bromine explosion.
A significant aspect of our current work is to measure the ozone mixing ratios in the Arctic as a function of time of year, and compare this data with other atmospherically relevant species (e.g. BrO).  The ozone measurement is done by a specialized 2B Technologies model 205 instrument (Figure 1).  This is a dual beam instrument that detects ozone in one cell while using the other cell as a blank.  The method of detection is absorbance of light (254 nm) emitted from a low pressure mercury lamp (Figure 2).  Some of the requirements for our research to be successful were for the instrument to have low power consumption, and to be stable over a wide range of temperatures.  The 2B instruments were found to be ideal in this respect as can be seen in Figures 3-4.