Rapid Loss of Particulate Nitrate, Chloride and Ammonium on Quartz Fiber Filters During Storage

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Abstract
The loss of particulate ammonium, nitrate, and chloride during storage of samples collected using PM-10 and standard high volume samplers in the Los Angeles Basin on filters of varying alkalinity, was investigated. For PM-10 samples collected on Whatman QM-A quartz fiber filters (av. filter pH = 8.6), losses of ammonium averaging 51 percent were observed after one week of storage in unsealed envelopes at room temperatures in laboratory air. The corresponding losses for nitrate and chloride were 19 percent and 65 percent, respectively. Volatilization of either NH4NO3 or NH4Cl could not account for the observed losses; alternate mechanisms are discussed. Whereas the rate of ammonium loss increased with increasing filter alkalinity, the reverse was found to be true for NO3- and Cl-. In the PM-10 study involving three stations, the loss rate for nitrate exhibited a site dependency with a decrease being observed on moving from a coastal (Long Beach) to an inland site (Riverside). The rate of nitrate decay, particularly at Riverside, showed a linear (time)1/2 dependence. No significant loss of particulate sulfate was observed for any of the filters (quartz, glass or Teflon-coated glass fiber) on storage for one month at ambient temperature.

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