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Unformatted text preview: Name:_____ KEY _______________ Chemistry 173 Midterm #2 Spring 2004 Total Points: /125 1. Two hypothetical atmospheric particle mass distributions are shown below. A transforms into B upon being exposed to high relative humidity (water vapor). Discuss the processes that lead to this shift at high relative humidity (i.e. extra water). Specifically, detail the composition differences between Modes 2 and 3 that lead to this shift. Note the size range of interest is 0.1-1 m (Modes 2 and 3 are accumulation mode particles). (12 points) Expose to high relative humidity 100 nm 50 nm 500 nm 1 m 100 nm 50 nm 500 nm 1 m g/m 3 g/m 3 A B Expose to high relative humidity 100 nm 50 nm 500 nm 1 m 100 nm 50 nm 500 nm 1 m 100 nm 50 nm 500 nm 1 m g/m 3 g/m 3 A B 3 1 2 1 2 Upon exposure to water, mode 2 splits into two particle size modes (2 and 3). The reason only certain particles grow is because these are composed of hydrophilic species (oxidized organic species and ions such as ammonium, nitrate, sulfate). Thus, mode 2 is composed of EC and hydrophobic OC species (i.e. long chain hydrocarbons). Mode 3 particles are composed of EC (possibly), hydrophilic OC species (i.e. acids, oxidized organic species), water soluble ions (i.e. ammonium, sulfate, nitrate), and water they absorbed upon exposure to high RH. 2. Provide the name of the most highly emitted biogenic (NMHC) VOC. Approximately, what fraction of the total global biogenic VOCs does it represent? (8 points) Isoprene, roughly 50% 3. Use the ozone isopleth below to explain whether this city is in a VOC- or NOx-limited regime (points are based on your reasoningguesses will be worth zero points). Given this information,...
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