Changes in Chemical Composition during Sampling

The preceding sections have outlined sampling systems designed to identify correctly the atmospheric gas and particulate phase distribution of collected organic material. An additional sampling artifact which has been little considered in the collection of atmospheric sampling is the potential alteration of organic compounds as a result of the sampling process. These alterations appear to result from the movement of ambient air containing oxidants and other reactive compounds past the collected particles. The addition of nO2 (<1 p.p.m.) or O3 (<200 p.p.b.) to the sampled air stream (0 to 5°C) for a high volume sampler reduced the concentrations of benzo(a) pyrene and benzo(a)anthracene from a few up to 38%, with the observed reduction increasing with increased concentration of the added gases. Spiking a filter with an amine resulted in an increase in measured concentrations of nitrosoamines in both the filter and a following XAD sorbent bed for a mid-volume sampler. Similar results have been obtained for the exposure of a deuterated amine on a filter to NOX. When Tenax columns spiked with deuterated styrene and cyclohexane were exposed to p.p.m. concentrations of ozone or halogens, oxygenated and halogenated compounds were shown to be formed. Similar oxidation of aldehydes and PAN during sampling has been observed. Collected PAH compounds can be oxygenated and/or nitrated on a filter but 1-nitropyrene has been shown to be resistant to additional nitration. These various chemical transformations of collected organic compounds can be eliminated by removal of the gas phase oxidants, NO„ HNO3, etc., prior to collection of the particles. The PC-BOSS denuder described above should be effective in eliminating most of chemical transformation artifacts since reactive gases are removed by the charcoal denuder which precedes the particle collection filter.

Solar Panel Basics

Solar Panel Basics

Global warming is a huge problem which will significantly affect every country in the world. Many people all over the world are trying to do whatever they can to help combat the effects of global warming. One of the ways that people can fight global warming is to reduce their dependence on non-renewable energy sources like oil and petroleum based products.

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