Atmospheric Chemistry, Ozone, UV Radiation, and Refrigerants

Comprehensive practice flashcards reviewing stratospheric and ground-level ozone formation, UV radiation spectrum and biological effects, sunscreen SPF efficiencies, and chemical properties of CFCs, HCFCs, and HFCs.

Why is ground-level ozone concentration usually higher on warm, sunny days compared to rainy, cloudy days?

Ground-level ozone concentration is higher on warm, sunny days because sunlight and heat drive the chemical reactions that create it. On rainy days, clouds and rainstorms block the UV solar radiation needed to power these photochemical reactions.

How do oxygen ($O_2$) and ozone ($O_3$) differ in chemical bonding, molecular structure, and polarity?

Oxygen consists of two oxygen atoms joined by a strong covalent double bond (bond order of $2$) in a linear, symmetrical, nonpolar structure. Ozone consists of three oxygen atoms in a bent structure with resonance structures, giving it a permanent dipole moment and making it a polar molecule.

What are the two steps involved in the natural formation of stratospheric ozone?

Step 1 (Photodissociation): High-energy UV radiation breaks the bond of an $O_2$ molecule, splitting it into two reactive single oxygen atoms. Step 2 (Binding Collision): Each freed oxygen atom collides and binds with an intact $O_2$ molecule, while a third neutral molecule (like nitrogen) absorbs excess energy to stabilize the newly formed $O_3$ molecule.

What are the primary sources of ozone at Earth's surface versus indoors?

At Earth's surface, ozone forms via chemical reactions between nitrogen oxides ($NO_x$) and volatile organic compounds (VOCs) in sunlight from motor vehicle emissions, power plants, boilers, refineries, and chemical plants. Indoors, it is generated by high-voltage electrical arcing inside laser printers, photocopiers, and fax machines, improper ozone generators marketed as air purifiers, and small electric motors.

Which atmospheric layer contains the highest concentration of ozone?

The stratosphere contains roughly $90\%$ of all atmospheric ozone.

What is the ozone hole, and what health and environmental impacts does it cause?

The ozone hole is a severe seasonal thinning of the stratospheric ozone layer over Antarctica that increases harmful UV-B radiation reaching Earth. In humans, it causes skin cancer, eye damage, immune suppression, and severe sunburns. In plants, it leads to stunted growth, reduced crop yields, and disrupted metabolism.

How does light wave energy relate to wavelength, and how do UV, visible, and infrared light compare?

Energy is inversely proportional to wavelength: shorter wavelengths carry higher energy. Ultraviolet (UV, $100\text{--}400\,nm$) has the highest energy, visible light ($400\text{--}700\,nm$) has moderate energy, and infrared ($700\,nm\text{--}1\,mm$) has the lowest energy.

What is the wavelength range of the visible spectrum and its individual colors?

The visible spectrum ranges from roughly $380$ to $750\,nm$: Red ($625\text{--}750\,nm$), Orange ($590\text{--}625\,nm$), Yellow ($565\text{--}590\,nm$), Green ($500\text{--}565\,nm$), Cyan ($485\text{--}500\,nm$), Blue ($450\text{--}485\,nm$), and Violet ($380\text{--}450\,nm$).

How do UVA, UVB, and UVC radiation compare in wavelength, atmospheric absorption, skin penetration, and health effects?

UVA ($315\text{--}400\,nm$): $95\%$ reaches Earth, penetrates deep into the dermis layer, causes aging, wrinkling, and long-term DNA damage. UVB ($280\text{--}315\,nm$): $5\%$ reaches Earth (mostly absorbed by ozone), penetrates shallowly into the epidermis layer, causes sunburn, skin reddening, and direct DNA damage. UVC ($100\text{--}280\,nm$): Completely absorbed by the ozone layer, superficial penetration (dead outer cells), highly mutagenic, and used as a germicide.

How do Lewis structures and bond orders differ between $O_2$ and $O_3$?

$O_2$ consists of a strong double covalent bond with a bond order of $2$, containing two shared electron pairs and two lone pairs on each oxygen atom. $O_3$ consists of resonance structures with a hybrid intermediate bond order of $1.5$ for both oxygen-oxygen bonds.

What are phytoplankton, and why are they important?

Phytoplankton are microscopic, plant-like organisms floating in the sunlit upper layers of oceans and freshwater bodies. They are important for oxygen production, climate regulation, food security, and acting as water quality indicators.

What biological damage does UV radiation cause to human DNA and eyes?

In DNA, UV causes adjacent thymine or cytosine bases to bond into cyclobutane pyrimidine dimers (CPDs) and 6-4 photoproducts, generates reactive oxygen species (ROS) leading to $8\text{-OHdG}$ lesions and strand breaks, and causes base-substitution mutations. In eyes, it causes snow blindness (cornea inflammation), lens clouding, conjunctiva growth, ocular melanoma, and macular degeneration.

What are the biological effects of UV radiation on plants, animals, and phytoplankton?

In plants: degrades D1 protein in Photosystem II, reduces photosynthetic efficiency, stunts size, and lowers crop productivity. In animals: impacts vision, immune health, behavior, lowers reproduction, and causes embryonic abnormalities. In phytoplankton: inhibits photosynthetic rates (reducing primary productivity in clear waters by up to $15\%$) and disrupts orientation, movement, and cell division.

What is the relationship between ozone, ozone-depleting substances, and global warming?

Ozone itself acts as a greenhouse gas, and the chemicals that damage the ozone layer also trap heat in the atmosphere.

What does SPF label on sunscreen measure, and what percentage of UVB rays are blocked by SPF 15, 30, 50, and 100?

SPF measures protection against UVB rays only. SPF 15 blocks about $93\%$ ($7\%$ allowed through), SPF 30 blocks about $97\%$ ($3\%$ allowed through), SPF 50 blocks about $98\%$ ($2\%$ allowed through), and SPF 100 blocks about $99\%$ ($1\%$ allowed through).

How do the chemical compositions of CFCs, HCFCs, and HFCs differ?

CFCs contain carbon, fluorine, and chlorine (no hydrogen), making them extremely stable in the lower atmosphere. HCFCs contain carbon, hydrogen, fluorine, and chlorine; the added hydrogen allows partial breakdown in the troposphere. HFCs contain carbon, hydrogen, and fluorine, but no chlorine atoms.

What are the environmental impacts (Ozone Depletion and Global Warming Potential) of CFCs, HCFCs, and HFCs?

CFCs have High Ozone Depletion and High GWP. HCFCs have Low Ozone Depletion and High GWP. HFCs have Zero Ozone Depletion and High GWP.