MChem Master of Chemistry Environmental Chemistry 1 — Questions and Answers
Question 1: What is the primary chemical reaction responsible for the formation of tropospheric ozone in urban smog?
- Direct emission of O3 from vehicles
- Photolysis of NO2 followed by O + O2 → O3 (Correct answer)
- Reaction of SO2 with sunlight
- Oxidation of methane by OH radicals alone
Correct answer: Photolysis of NO2 followed by O + O2 → O3
Tropospheric ozone forms when UV light photolyzes NO2 to produce atomic oxygen, which then combines with O2 to form O3.
Question 2: Which greenhouse gas has the highest global warming potential (GWP) on a per-molecule basis over a 100-year horizon?
- Carbon dioxide (CO2)
- Methane (CH4)
- Sulfur hexafluoride (SF6) (Correct answer)
- Nitrous oxide (N2O)
Correct answer: Sulfur hexafluoride (SF6)
SF6 has a GWP of approximately 23,500 over 100 years, making it the most potent greenhouse gas regulated under the Kyoto Protocol.
Question 3: What chemical process converts dissolved CO2 in the ocean to carbonic acid, contributing to ocean acidification?
- CO2 + H2O → H2CO3 (Correct answer)
- CO2 + 2H2O → CH4 + O2
- CO2 + NaCl → Na2CO3 + Cl2
- CO2 + CaCO3 → Ca(HCO3)2
Correct answer: CO2 + H2O → H2CO3
CO2 dissolves in seawater and reacts with water to form carbonic acid (H2CO3), which dissociates to lower ocean pH.
Question 4: What is the Henry's Law constant used to describe in environmental chemistry?
- The rate of photodegradation of pollutants
- The equilibrium partitioning of a chemical between air and water (Correct answer)
- The adsorption of contaminants onto soil particles
- The biodegradation rate of organic compounds
Correct answer: The equilibrium partitioning of a chemical between air and water
Henry's Law constant (KH) describes the ratio of a chemical's concentration in the gas phase to its concentration in aqueous solution at equilibrium.
Question 5: Which process describes the increase in concentration of persistent pollutants (e.g., PCBs) at higher trophic levels in a food chain?
- Bioaccumulation
- Biodegradation
- Biomagnification (Correct answer)
- Biotransformation
Correct answer: Biomagnification
Biomagnification is the progressive increase in concentration of lipophilic, persistent pollutants as they move up the food chain from prey to predator.
Question 6: What is the role of hydroxyl radicals (•OH) in tropospheric chemistry?
- They catalyze stratospheric ozone depletion
- They act as the atmosphere's primary oxidant, initiating degradation of VOCs and methane (Correct answer)
- They are the main cause of acid rain
- They absorb UV radiation in the stratosphere
Correct answer: They act as the atmosphere's primary oxidant, initiating degradation of VOCs and methane
Hydroxyl radicals are the dominant oxidant in the troposphere, reacting with VOCs, CH4, and CO to initiate their atmospheric degradation.
MChem Master of Chemistry Environmental Chemistry 1
What is the primary chemical reaction responsible for the formation of tropospheric ozone in urban smog?