| Περίληψη: | Atmospheric aerosol contains a variety of both inorganic and organic species and plays a significant role in atmospheric chemistry and physics. Organic compounds are usually the dominant component of the submicrometer particles contributing around 50% of its mass. One of the most important physical properties of organic aerosol is volatility which determines its gas-to particle partitioning and provides both direct information about its origin and indirect information about its chemical composition and age.
The objectives of the Thesis are to measure the volatility distributions of OA produced from olive tree branches burning and of ambient organic aerosol mainly attributed to residential wood burning in Athens. A thermodenuder system operating in a range of residence times was used to measure the aerosol fraction that remains after partial heating. The operation of the thermodenuder system was tested with ammonium sulfate model aerosol. Ammonium sulfate particles are easily produced and behave as non-volatile at lower temperature (25-75oC), as semivolatile at intermediate temperatures (75-120o) and evaporate completely at higher temperatures (T≥ 150oC). Thermodenuder wall losses were determined for our system using sodium chloride particles which are non-volatile even at 500oC. These results are used to post correct the thermodenuder measurements.
Fifty percent of the OA produced during olive tree branches burning evaporated at 113oC at 15.8 s in our thermodenuder. For temperatures higher than 150oC no evaporation occurred. This was attributed to reactions that probably took place inside the thermodenuder at such high temperatures. The post correction of measurement resulted on average in 15-20% increase of the Mass Fraction Remaining values. Fitting our measurements with a thermodenuder dynamic model resulted in a wide volatility distribution including OA with effective saturation concentrations from 10-2-102 μg m-3, vaporization enthalpy of 68±18 kJ mol-1 and mass accommodation coefficient in the range 0.01-0.14. The gas-to-particle partitioning behavior of the produced aerosol from olive tree branches burning was consistent with recent studies for a range of fuels.
Ambient organic aerosol volatility was also determined for wood burning periods in Athens. The estimated volatility distribution of ambient organic aerosol from the thermodenuder dynamic model showed that almost 80% of ambient organic aerosol during the burning periods can be characterized as semivolatile while the other 20% has low volatility. The gas-to-particle partitioning determination showed that the ambient organic aerosol during burning periods in Athens is a little more volatile than both the organic aerosol of wild fires of recent studies in the US and the organic aerosol of olive tree branches burning.
The volatility distributions and enthalpies of vaporization obtained in this study can be used as inputs to Chemical Transport Models simulating the emission, dispersion, and chemical evolution of OA from wood burning.
|
|---|
