University of Amsterdam
On-line chemical analysis of inorganic species in atmospheric particulate matter and their related trace gasses: Instrument recovery and validation of a new instrument
Master research thesis of my 4 month research period at the Peking University
Roeland Jansen
July 2009
On-line chemical analysis of inorganic species in atmospheric particulate matter and their related trace gasses: Instrument recovery and validation of a new instrument
By Roeland Jansen, 5949475
University of Amsterdam, Master Chemistry, Track Analytical Sciences
Master coordinator: Doctor Wim Theodore Kok
Date of research: February 14th – June 14th 2009
Research institute: Peking University, Beijing P.R. of China
Research group: College of Environmental Sciences and Engineering
Daily supervisor: Professor Min HU
Abstract
Atmospheric particulate matter (PM) contributes to air pollution. PM has an adverse effect on human health, it decreases visibility and contributes to climate change. Furthermore when deposition happens, species in PM can lead to changes in plant and animal communities. PM can be directly emitted in the air, primary aerosols, and it can be formed by homo- or heterogeneous reactions in the atmosphere, secondary aerosols. Both primary and secondary aerosols can origin from both natural and anthropogenic sources. The chemical composition of PM is a fundamental property related to above mentioned environmental issues and to understand which species are responsible for which effects the composition needs to be studied. The classical filter based technique for PM sampling and collecting requires long term sampling and hence results in average concentrations, leads to over- or underestimations of concentrations due to artifacts and is labor intensive to perform. This has led to the development of on-line and high sample frequency instruments for sampling, collecting and analyzing PM.
An instrument called the Steam Jet Aerosol Collector (SJAC) has been developed at the Energy Research Centre of the Netherland (ECN, Petten The Netherlands). The SJAC has been successfully used in field campaigns as on-line high resolution instrument to measure concentrations of inorganic species in aerosols (NH4+, Cl-, NO2-, NO3-, SO42-) simultaneously with water soluble acidic trace gasses (SO2, HNO3, HNO2, HCl) and ammonia (NH3). The simultaneous measurement of inorganic species in PM and acidic trace gases and ammonia is of high interest to study their relation. A version of this instrument was donated to the Peking University (PKU, Beijing P.R of China) several years ago. The condition of the instrument is not good and it has been partly recovered in this study. Further work needs to be done before this instrument can be used in field campaigns again.
An instrument called the Gas Aerosol Collector (GAC) has been developed at the Peking University. The methodologies for gas and aerosol sampling are based on the principles of the ones used the SJAC. The GAC is significantly more robust and easier to use and transport, the control and data acquisition are up to date and hence it is friendlier to its users. The performance (i.e. the efficiency of the devices to collect gasses and aerosols) of the GAC has been partly validated during this study. The efficiency has been tested by sampling artificial aerosols and standard certified gases. Several artifacts were observed which consequently lead to over- or underestimation of the signals. Primarily results show a relation between aerosol concentration and aerosol loss in the inlet part, leading to underestimation in aerosol results and overestimation in the related gas results. The collection efficiency of the aerosol collector for artificial generated (NH4)2SO4 aerosols is larger than 99%. Further validating of the GAC needs to be performed before accurate measurements of the inorganic composition of PM and related water soluble trace gases can take place and recommendations are given to do so.
The physical properties of artificial generated (NH4)2SO4 particles were studied by the use of a commercial aerosol generator (TSI Atomizer) coupled to a scanning mobility particle sizer (SMPS) and a condensation particle counter (CPC). Clear changes in physical properties are observed when changing the settings of the atomizer.
Keywords: Inorganics, aerosols, ammonia, acidic trace gases, wet rotating denuder, aerosol collector, efficiency, artifacts, SMPS, CPC.