Effects of Other Compounds on 4-Nitrophenol

After developing and optimizing the photolysis of 4-Nitrophenol alone, we then moved on to a controlled experiment comparing the photolysis of 4-Nitrophenol alone to the photolysis of 4-Nitrophenol with secondary organic aerosol (SOA). We kept the concentration of 4-Nitrophenol constant with earlier trials and tried to model cloudwater concentrations of SOA. The SOA was prepared by other members of the lab and concentrated in vials. We extracted the SOA with water and added a dilute amount into solution with the 4-Nitrophenol. We then repeated the procedures of the earlier experiments: quartz vial wrapped with foil under xenon arc lamp. This experiment was repeated three times to isolate variables. Once with brown carbon only, once with SOA only, and once with both together. This experiment was conducted toward the end of the summer, so the data requires more analysis. The SOA, however, did not seem to affect the rate of photolysis as much as predicted.

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Photolysis of 4-Nitrophenol

After gaining some experience with our methods and instruments, we were able to really get to work on matching the literature data. In order to test the effects of other compounds (such as secondary organic aerosols or inorganics) on the lifetime of brown carbon, we had to achieve a good and reproducible baseline measure of how it reacted to sunlight on its own. To do this, we created a very dilute solution of 4-Nitrophenol (a type of brown carbon) and placed it in a quartz vial. The quartz lets more wavelengths of light through than glass or other materials. This vial was placed in front of a xenon arc lamp that simulated the wavelengths and energy of sunlight. We found that using a stir bar and backing the vial with reflective foil maximized the rate of photolysis. At different time intervals (1 hour time intervals shown in the following figure) we took aliquots of the solution and analyzed the sample using the UV/VIS spectrophotometer.

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First Month: Method Development

Before we got the photolysis lamp (a xenon arc lamp), we did some preliminary trials by exposing the brown carbon to sunlight the old fashioned way.

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