Aerosol is defined as the gas or liquid particle suspended in the air. Aerosol with aerodynamic diameter less than 2.5μm is collectively defined as PM2.5, which is formed during primary combustion process or through atmospheric oxidative reactions involving nucleation, condensation or coagulation.
Aerosol is made up of various components, including inorganic ions, carbonaceous materials and elements. Carbonaceous material, composed of two different kinds of substances, elemental carbon (EC) and organic carbon (OC), constitutes the most significant part of PM2.5. Approximately 40% of PM2.5 mass are accounted for it . EC is formed through incomplete combustion of fossil fuels such as vehicular emission while OC is mainly formed through primary combustion like biomass burning or from secondary oxidation processes in the atmosphere.
Aerosol exerts both direct and indirect effect to the Earth’s radiative forcing. Direct effect is due to the capability of aerosol to absorb and scatter light. Indirect effect to radiative forcing is defined as the disturbance to the radiation balance to the Earth’s atmosphere. Polar organic chemicals are significant fraction of OC in the ambient; understanding of the chemical structures and concentration of them can assist in the prediction of climate models and hence explain the change in global climate by aerosol properties.
Gas Chromatogram (GC) can separate different gaseous organic compounds according to their polarity and structure, thus different kinds of OC can be segregated and have different retention time. Mass Spectrum (MS) is an analytical instrument in which fragment ions, produced from a chemical by high-energy ion source bombardment, are separated by electric or magnetic fields according to their ratios of charge to mass (m/z). A record of the types of ion present and their relative amounts is produced.
An in-situ derivatization thermal desorption method followed by gas chromatography and mass spectrometry (IDTD-GC-MS) is developed for determination of polar organic compounds. The advantage of IDTD is the reduction of analytes losses and memory effects by desorption of the sample within the GC injector. Derivatization is based on silylation with N-Methyl-N-trimethyl-silyltrifluoroacetamide (MSTFA) during the step of thermal desorption |
