Using the environmental scanning electron microscope for studying the atmospheric transformations of organic and inorganic particles
EMSL Project ID
3575
Abstract
Atmospheric aerosols are widely recognized as key elements in many environmental issues ranging from global climate change and visibility, through modification of the hydrological cycle to adverse affects on people's health. Aerosols affect climate and rain formation via interactions with incoming solar radiation (the direct radiative effect) and through modifications of cloud properties (1st and 2nd indirect effects). Health effects are due to small-sized aerosols that often contain carcinogenic and mutagenic compounds and are efficiently transported into the lungs. During the atmospheric lifetime, aerosols change their properties by various processes, including reactions, adsorption, absorption and coatings by hydrophobic and hydrophilic layers.We suggest to study the effect of aerosol transformation on the hygroscopic properties of the particles. We will focus on two types of particles: pure organics and mineral dust.
a. Pure organic: Objectives: 1. can chemical transformations of saturated compounds lead to the formation of hygroscopic aerosols? 2. Do organic aerosols change their sizes, under dry condition, due to reaction with ozone? Are the product forming a layer or are they well mixed in the aerosols? Approach: oleic and linoleic acid particles, produced by atomizing a 5% mixture in methanol, will be deposited on TEM grids The aerosols will be characterized in the ESEM with respect to their shape, size distribution and response to RH. The particles will then be exposed to ozone (20-200 ppb) for different length of time. Following reaction, they will be re-characterized to probe changes in morphology, size and hygroscopic properties. Using SIMS-TOF the distribution of the product (presumable dicarboxylic acid such as azelaic acid) will be studied.
b. Interaction of mineral dust with organic acid and PAHs. Objectives: 1. Study the uptake of organic acids (oxalate and acetate) by CaCO3 and CaSO4 dust particles. 2. Understand the effect of RH on the uptake ? is there a reaction between dissolved ions and the acid? Does a quasi liquid like layer form and assist acid uptake? Do PAH alter the mineral dust particles hygroscopic properties and how reactions of the PAH affect the particles properties? Approach: CaCO3 and CaSO4 particles will be exposed to acetic and oxalic acid in the gas phase as a function of increasing RH. We will follow the morphological transformation of the particles and identify the resulting surface layers (or microcrystals) on the reacted particles. Specifically we will look for the formation of calcium oxalate and calcium acetate crystals, which are not soluble. In addition, bezo[a]pyrene (BaP) will be adsorbed onto CaCO3 particles ranging from submonolayer to a monolayer. The coated particles will be exposed to RH prior o and following exposure to ozone. The effect on the hygroscopicity will be probed.
c. The effect of organic coating on chemical reactions of mineral dust particles: Objectives: study how organic layers, and organic layers properties, affect mass transfer into aerosols, and the hygroscopic properties of aerosols. Approach: Coat CaCO3 particles by an organic coating of a long chained organic compounds (alkanes and alkenes). The uptake of HNO3 as a function of coating thickness will be followed by observing the formation of CaNO3 in the particles. The deliquescence RH of the particles as a function of coating thickness and type will be probed. The same experiments will be studied after reaction of the organic layer with an oxidant. The effect of the degradation on the rate of mass transfer will be probed. The same experiment will be repeated for sea salt, and the effect of Cl depletion and hygroscopic response will be studied. Weizmann will be able to supply the coated particles, as well as perform some of the experiments with its own ESEM system
Project Details
Project type
Exploratory Research
Start Date
2003-10-01
End Date
2005-10-02
Status
Closed
Released Data Link
Team
Principal Investigator
Related Publications
Laskin A, MJ Iedema, A Ichkovich, ER Graber, I Taraniuk, and Y Rudich. 2005. "Direct Observation of Completely Processed Calcium Carbonate Dust Particles." Faraday Discussions 130:453 - 468.