The Effect of Filter Storage Techniques on Thermal and Optical Degradation of Combustion Aerosol Samples
CHASE GLENN, Omar El Hajj, Kruthika Kumar, Rawad Saleh,
University of Georgia Abstract Number: 596
Working Group: Instrumentation and Methods
AbstractAerosols are often collected on filters for offline analyses weeks after sample collection. Current practices involve wrapping filters with aluminum foil and storing in a freezer to prevent sample degradation. However, evidence supporting these practices is lacking. Here, we examine the effect of thermal and photo degradation on aerosol samples generated from the combustion of pine needles and toluene. The aerosols were collected on quartz and Teflon filters. The quartz filters were analyzed for their organic and elemental carbon content using an OCEC analyzer. The Teflon filters were extracted, and the imaginary part of the refractive index (k) was retrieved from light-absorption measurements using a UV-vis spectrometer. Each filter was divided into four pieces. One was analyzed immediately (control), and the others were stored for a month at three conditions: (A) covered and in a freezer, (B) covered at room temperature, and (C) uncovered at room temperature.
For both pine and toluene combustion aerosol, storage condition A ensured OC/EC results identical to control. On the other hand, B and C led to reduction in OC1 fraction, especially at C, which can be attributed to evaporation of semi-volatile OC. For pine combustion, k at 422 nm (k
422) at A and B were close to control. On the other hand, k
422 increased by 21% for C, suggesting that the evaporated OC is less absorptive than the residual OC, leading to an overall increase in k
422. For toluene combustion, k
422 decreased relative to control by 20%, 18%, and 10% for A, B, and C, respectively. This can be explained by two competing effects: (i) degradation of chromophores at all conditions, and (ii) evaporation of the less absorbing OC fraction in C leading to larger k
422 compared to A and B.