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This glossary contains all the vocabulary words which are defined in all of the modules. For module-specific glossaries, see the overview page for each module.



acid rain - rainfall made sufficiently acidic by air pollution that it causes environmental harm, typically to forests and lakes. The main cause of acid rain is combustion of fossil fuels, which produces waste gases that contain sulfur and nitrogen oxides, which combine with water vapor to form acids. Other forms of acid precipitation are also possible.


air toxics - pollutants that cause or may cause cancer or other serious health effects, such as reproductive effects or birth defects, or adverse environmental and ecological effects. Also known as toxic air pollutants or hazardous air pollutants


airshed – an area of land that shares a common air flow. The Chesapeake Bay nitrogen airshed is the area of land where most of the nitrogen air pollution to the Chesapeake Bay comes from


algae (singular alga) - simple, nonflowering, and typically aquatic organisms of a large group that includes the seaweeds and many single-celled forms. Algae contain chlorophyll but lack true stems, roots, leaves, and vascular tissue

algae bloom - a rapid increase in the population of algae in an aquatic system

ammonium (NH4)+  – an ion that is related to ammonia (NH  ). Both ammonium and ammonia are common air pollutants that are produced from agriculture and industry.

alveoli (singular alveolus) - tiny sacs in the lungs of mammals (including humans) that allow gases to transfer between the lungs and capillaries. This allows gases to enter and leave the bloodstream.

anemometer – a scientific instrument for measuring wind speed


AQI (Air Quality Index) – a scale for reporting daily air quality. The AQI tells you how clean or polluted the air is in a given location, and what the associated health risks are. The AQI focuses on health effects you may experience within a few hours or days after breathing polluted air.


arsenic – an element that occurs naturally in Earth’s crust, and is commonly found in water, air, and soil. In high enough quantities or in the case of long-term exposure, arsenic can cause significant health problems

artery – a muscular tube that is a part of the circulatory system, which carries blood (mainly oxygen-rich) from the heart to all parts of the body.



barometer – a scientific instrument for measuring air pressure


brackish - slightly salty, like the mixture of river water and seawater in estuaries


bronchi (singular bronchus) - passages or airways in the respiratory system that conduct air into the lungs


bronchodilator - a medication that relaxes and opens the airways, or bronchi, in the lungs.



cadmium – an element that occurs naturally in Earth’s crust. Cadmium can be released to the air as a result of industrial processes. Inhaling cadmium fumes can be highly hazardous to health.


capillary – a fine, branching blood vessel that connects the arteries to the veins in the circulatory system

carbon dioxide (CO2) – a colorless, odorless gas produced by burning carbon and organic compounds such as fossil fuels, and by cellular respiration. It is naturally present in air (about 0.03 percent) and is absorbed by plants in photosynthesis. Carbon dioxide is also a major greenhouse gas.

carbon footprint – the amount of carbon dioxide and other carbon compounds emitted due to the consumption of fossil fuels by a particular person, group, etc.


carbon monoxide (CO) - an odorless, colorless gas formed by the incomplete combustion of fuels. Can lead to poisoning because CO molecules will displace the oxygen in red blood cells.


cardiovascular disease – a health condition that involves narrowed or blocked blood vessels that can lead to a heart attack, chest pain, or stroke.


cardiovascular system – another name for the circulatory system which references the heart (cardio-) and blood vessels (-vascular)


causation – a change in one variable directly resulting in the change of another variable through a direct mechanism


climate – the weather conditions in a given area over a long period of time, ex. temperature and rainfall

climate change – any significant change in the measures of climate lasting for an extended period of time. In other words, climate change includes major changes in temperature, precipitation, or wind patterns, among other effects, that occur over several decades or longer.


climate resilience – the ability to anticipate, prepare for, and respond to hazardous events, trends, or disturbances related to climate.


Code Red Day – a day when the air quality index (AQI) is in the red zone (151-200) meaning that the air is unhealthy for everyone to breathe.


combustion – the chemical process of burning. Combustion requires a fuel that is burned using oxygen in a chemical reaction that produces carbon dioxide and water. See also incomplete combustion.

community climate resilience - the ability of communities to prepare for, respond to, and recover from hazardous events and adversity related to climate change.

control – a variable which is kept constant across groups in a controlled experiment in order to isolate the effects of the other variables


COPD (chronic obstructive pulmonary disease) - a group of related diseases that cause airflow blockage and breathing-related problems. COPD includes emphysema and chronic bronchitis.

correlation – a mutual relationship or connection between two or more things. Often shown as a relationship between two variables or quantities in a graph or chart

criteria pollutant – any one of the six air pollutants that are regulated by the EPA as required by the Clean Air Act. The criteria pollutants are carbon monoxide, lead, nitrogen dioxide, ozone, particulate matter, and sulfur dioxide



dead zone – a low-oxygen, or hypoxic, area of water that can be deadly to aquatic life

decomposer – an organism that breaks down dead or decaying organisms


dependent variable – a variable that is measured by the experimenter in a

controlled experiment, and whose value depends upon the independent variable


deposition – the process by which substances are “deposited” on the land or in the water. In the case of air pollution, deposition refers to air pollution from the atmosphere is deposited on land or in the water


dew point - the atmospheric temperature below which water droplets begin to condense and dew can form


diesel – a type of fuel made from oil that is used in specialized combustion engines (diesel engines) where it is ignited through compression as opposed to a spark in more common combustion engines

dissolve (as a substance) – to become incorporated into another substance so as to form a solution. Most commonly, when a solid or gas is dissolved into a liquid


dissolved oxygen – oxygen molecules that are dissolved in and which is available to living aquatic organisms. 

dry deposition – the process by which air pollution is deposited directly from the atmosphere, either as a gas or a solid



ecosystem – a biological community of interacting organisms and their physical environment

environmental justice - the fair treatment and meaningful involvement of all people regardless of race, color, national origin, or income, or any other personal characteristic with respect to the development, implementation, and enforcement of environmental laws, regulations, and policies.


estuary – a partially enclosed, coastal water body where freshwater from rivers and streams mixes with salt water from the ocean. Estuaries, and their surrounding lands, are places of transition from land to sea.

eutrophication – an excessive amount of nutrients in a lake or other body of water, frequently due to runoff from the land, which causes a dense growth of plant life and may cause the death of animal life from lack of oxygen.



fish kill – the sudden and unexpected death of a number of fish or other aquatic animals such as crabs or prawns over a short period of time and often within a particular area in the wild.


food web – a model showing how energy and matter are transferred in an ecosystem by indicating what organisms eat or are decomposed by other organisms


fossil fuel – a natural fuel such as coal or gas, formed in the geological past from the remains of living organisms.



geosphere – the solid components of Earth in comparison to the hydrosphere, atmosphere, and biosphere.


global warming – recent and ongoing rise in global average temperature near Earth's surface. It is caused mostly by increasing concentrations of greenhouse gases in the atmosphere.


greenhouse effect – the trapping of the sun's warmth in a planet's lower atmosphere by particular gases


greenhouse gas - a gas that contributes to the greenhouse effect by absorbing infrared radiation (heat), e.g., carbon dioxide and chlorofluorocarbons.



hemoglobin - a protein in human red blood cells that carries oxygen to the body's organs and tissues and transports carbon dioxide from organs and tissues back to the lungs.


humidity – a measure of the amount of humidity in the atmosphere

hydrosphere - all the waters on or below the earth's surface, such as aquifers, lakes, and seas. Sometimes hydrosphere is also used to refer to water vapor in the form of clouds.


hygrometer – a scientific instrument for measuring humidity.



incomplete combustion – a type of combustion that takes place when the supply of oxygen is poor. This results in a higher proportion of carbon monoxide gas and solid carbon (soot) being produced instead of carbon dioxide. Water is still a product of incomplete combustion.


independent variable – a variable that is changed by the experimenter in a controlled experiment


Inversion – a weather condition wherein a layer of cool air is trapped at the surface by a warmer air layer over it. Inversions can trap air pollution near the surface because the cool air will not rise into the warmer air. Also known as a temperature inversion.



land ice – frozen water that is on land, including mountain glaciers and ice sheets covering Greenland and Antarctica


lung function – a term used to describe how well the lungs work in helping a person breathe. Lungs function is measured by lung size, air flow, and other aspects of lung health.



menhaden – a common fish found in the Chesapeake Bay. Also known as mossbunker and bunker


micrometer/micron (symbol: µ) – a unit of length equal to one-millionth of a meter (0.000001 m). Micrometer is the SI unit of measure, while micron is the former name of the unit which is still in common use.


MWEE (Meaningful Watershed Educational Experience) – an investigative or experimental project that engages students in thinking critically about the Chesapeake Bay watershed



nitrate (NO3)-  – an ion that is a common component of fertilizers. Nitrate often forms when nitrogen dioxide (an air pollutant) reacts with other pollutants and dissolves in water vapor. Nitrate is common component of nutrient pollution.


nitrogen – an element found abundantly in the Earth’s atmosphere. When combined with oxygen, nitrogen forms nitrogen oxides (NOx), a common form of air pollution and a contributor to nutrient pollution


nitrogen dioxide (NO2) – a highly reactive gas that is a common air pollutant. Nitrogen dioxide primarily comes from burning fossil fuels in power plants, cars, trucks, and other vehicles.


nutrient pollution – the process where too many nutrients, mainly nitrogen and phosphorus, are added to bodies of water and can act like fertilizer, causing excessive growth of algae.



ozone (O3) - a natural and a man-made gas made of three oxygen atoms that occurs in the Earth's upper atmosphere (the stratosphere) and lower atmosphere (the troposphere). Depending on where it is in the atmosphere, ozone affects life on Earth in either good or bad ways.



particulate matter (abbreviation: PM) - a mixture of solid particles and liquid droplets found in the air. Some particles, such as dust, dirt, soot, or smoke, are large or dark enough to be seen with the naked eye. Larger particles are called PM 10, smaller particles are called PM 2.5, based on their diameter in micrometers.

parts-per-billion (abbreviation ppb) – a unit of measure equal to 1 in 1 billion, or 0.0000001%. 1 ppb is also equivalent to 1 µg/liter.


parts-per-million (abbreviation ppm) – a unit of measure equal to 1 in 1 million, or 0.0001%. 1 ppm is also equivalent to 1 mg/liter.


phosphate (PO4)3- – an ion that is a common component of fertilizers. Phosphate is a common component of nutrient pollution.

phosphorus – a metallic element that commonly combines with oxygen to form the phosphate ion. In this form, phosphorus is a common contributor to nutrient pollution



rain gauge - a device for collecting and measuring the amount of rain which falls

RCP (Representative Concentration Pathway) – a greenhouse gas concentration (not emissions) trajectory. The pathways describe different climate futures, all of which are considered possible depending on the volume of greenhouse gases (GHG) emitted in the years to come

runoff – water flowing across the ground’s surface, which often carries things with it



sea ice – frozen, floating ocean water

sky condition – a measure of the percentage of the sky covered by opaque clouds.

sediment – sand or stones that are carried into a body of water (or onto land) from wind, water, or ice

smog – a haze caused by air pollution. Smog that is made of ground-level ozone is created when sunlight shines on particular kinds of air pollution and nitrogen oxides, especially from automobile exhaust. Smog can also refer to a haze caused by particulate matter pollution.

soot – a black powdery or flaky substance consisting largely of amorphous carbon, produced by the incomplete burning of organic matter including fossil fuels.

stomata (singular stoma) – a pore, found in the epidermis of leaves, stems, and other organs, that controls the rate of gas exchange into and out of plants.

stratosphere - the layer of the earth's atmosphere above the troposphere, extending from about to about 4-8 miles above the Earth’s surface to about 32 miles (50 km)


sulfur dioxide (SO2) – a toxic gas that is often released when coal that contains sulfur is burned in a power plant

sunny day flooding – temporary flooding of low-lying areas, especially streets, during exceptionally high tide events, such as at full and new moons. Also known as nuisance flooding or tidal flooding.



tide – the alternate rising and falling of the sea, usually twice in each lunar day at a particular place, due to the attraction of the moon and sun.

trachea (in human anatomy) – a large membranous tube reinforced by rings of cartilage, extending from the larynx to the bronchial tubes and conveying air to and from the lungs. Also known as the windpipe


troposphere – the lowest region of the atmosphere, extending from the earth's surface to a height of about 4-8 miles (6–10 km), which is the lower boundary of the stratosphere.




urban heat island – a phenomenon wherein an urban area or metropolitan area is significantly warmer than its surrounding rural areas due to human activities.


vein – a tube that is part of the circulatory system of the body, which carries blood (mainly oxygen-poor) toward the heart.


watershed – an area of land that drains into a specific body of water


weather – the state of the atmosphere at a given place and time in terms of

temperature, humidity, precipitation, wind, etc.


wet deposition – the process by which air pollution is deposited by mixing with precipitation

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