AP Environmental Science: Modules 46 + 47

How does acid deposition form (not just acid rain!)? Why has it improved in the US and yet become worse elsewhere in the world?

... Acid deposition, commonly known as acid rain, occurs when emissions from the combustion of fossil fuels and other industrial processes undergo complex chemical reactions in the atmosphere and fall to the earth as wet deposition (rain, snow, cloud, fog) or dry deposition (dry particles, gas). Rain and snow are already naturally acidic, but are only considered problematic when less than a pH of 5 (see ph scale). The main chemical precursors leading to acidic conditions are atmospheric concentrations of sulfur dioxide (SO2) and nitrogen oxides (NOx). When these two compounds react with water, oxygen, carbon dioxide, and sunlight in the atmosphere, the result is sulfuric (H2SO4) and nitric acids (HNO3), the primary agents of acid deposition. Because nitrogen oxides are created in the process of burning coal and other fossil fuels, some power plants are changing the way they burn coal. A great way to reduce acid rain is to produce energy without using fossil fuels. Instead, people can use renewable energy sources, such as solar and wind power.

What time of day would you expect tropospheric/ground-level ozone to peak?

A Day in the LIFE OF OZONE Ozone concentrations in the atmosphere build up and dissipate through the course of a typical day as the weather, amount of sunlight, and number of cars on the road change. O3: Ozone Daily Ozone Patterns Smog Facts Infographic EARLY MORNING The formation of ground-level ozone gets started early in the morning. As we begin the day's activities practically everything we do, from plugging in the toaster to driving our cars to work, generates ozone-forming air pollution. The most significant of these are volatile organic compounds and nitrogen oxides. Vehicular traffic is by far the largest source of precursors. LATE MORNING After the commute is over, continued traffic emissions added to the earlier pollution begins to form ozone as the sun's heat and light intensifies. During warm summer months, an inversion may develop and trap the pollutants close to the ground (400-500 feet above sea level). If there is little wind, the pollution dispersion may be further restricted. MID-AFTERNOON By mid-afternoon, the sun has reached its apex and temperatures peak. The sun's radiation will cause a chemical reaction between the volatile organic compounds and nitrogen oxides to form ozone. Temperatures in the 90's or above are required for maximum ozone concentrations.

Why is air pollution considered a global system?

Air pollution is the introduction of chemicals, particulate matter, or microorganisms into the atmosphere at concentrations high enough to harm plants, animals, and materials such as buildings, or to alter ecosystems. Since one of the major repositories for air pollutants is the atmosphere, which envelops the entire globe, we must think of the air pollution system as a global system. For example, in recent years, air pollution in Asia has been responsible for acidic rainfall on the West Coast of the United States.

What are natural vs. anthropogenic sources of air pollution?

Natural sources of air pollution include volcanoes, lightning, forest fires, and plants both living and dead, which all release compounds than can be classified as pollutants. In contrast to natural emission, emissions from human activity, called anthropogenic sources of air pollution, are monitored, regulated, and in many cases controlled. Anthropogenic sources include on-road vehicles, power plants, industrial processes, and waste disposal.

Why are VOCs considered air pollutants?

Organic compounds that evaporate at typical atmospheric temperatures are called volatile organic compounds (VOCs). Many VOCs are hydrocarbons-- compounds that contain carbon-hydrogen bond, such as gasoline, lighter fluid, dry-cleaning fluid, oil-based paints, and perfumes. Compounds that give off a strong aroma are often VOCs since the chemicals are easily released into the air. VOCs play an important role in the formation of photochemical oxidants such as ozone. VOCs are not necessarily hazardous; many, such as VOCs given off by conifer trees, cause no direct harm. VOCs are not currently considered a criteria air pollutant, but because they can lead to to the formation of photochemical oxidants, they have the potential to be harmful and are therefore of concern to air pollution scientists.

What is PM and where does it come from?

Particulate matter (PM), also called particulates or particles, is solid or liquid particles suspended in air. Particulate matter comes from the combustion of wood, animal manure and other biofuels, coal, oil, and gasoline. It is most commonly known as a class of pollutants released from the combustion of fuels such as coal and oil. Diesel-powered vehicles give off more particulate matter, in the form of black smoke, than do gasoline-powered vehicles. Particulate matter can also come from road dust and rock-crushing operations. Volcanoes, forest fires, and dust storms are important natural sources of particulate matter.

How does the size of PM affect our concern about it?

Particulate matter ranges in size from 0.01 micrometer to 100 micrometers. For comparison, a human hair has a diameter of roughly 50 to 100 micrometers. Particulate matter larger than 10 micrometers is usually filtered out by the nose and throat; particulate matter of this size is not regulated by the EPA. Particles smaller than 10 micrometers are called Particulate Matter-10, and are of concern to air pollution scientists because they are not filtered out by the nose and throat and can be deposited deep within the respiratory trace. Particles of 2.5 micrometers and smaller are an even greater health concern because they deposit deeply within the respiratory tract and they tend to be composed of more toxic substances than particles in larger size ranges.

What is photochemical smog?

Photochemical smog is dominated by oxidants such as ozone and is sometimes called Los Angeles-type smog or brown smog. In the presence of sulfur and nitrogen oxides, photochemical oxidants can enhance the formation of scattering light. The resulting mixture is called smog, a mixture of oxidants and particulate matter. The word is derived by combining smoke and fog. Smog is partly responsible for the hazy view and reduced sunlight observed in many cities.

How do you distinguish between primary and secondary pollutants?

Primary pollutants are polluting compounds that come directly out of a smokestack, exhaust pipe, or natural emission source. Secondary pollutants are primary pollutants that have undergone transformation in the presence of sunlight, oxygen, water, or other compounds. Because solar radiation provides energy for many of these transformations, and because water is usually involved, the conversion to secondary pollutants occurs more rapidly during the day and in wet environments.

Why does a temperature inversion increase air pollutants at the land surface?

Temperature inversions affect air pollution because they change the dynamics of air movement. Warm air rises in the atmosphere because it is less dense and, therefore, more buoyant than the cooler air above it. This tendency to rise is what creates the vertical development found in thunderstorms. However, a temperature inversion prevents this vertical movement, also known as convection. Stated differently, inversions function like an atmospheric lid or blanket. This smothering effect traps air pollutants and allows their concentrations to increase.

How does the AQI present in air quality?

The AQI focuses on health effects you may experience within a few hours or days after breathing unhealthy air. The AQI is calculated for four major air pollutants regulated by the Clean Air Act: ground level ozone, particle pollution, carbon monoxide, and sulfur dioxide.

What is the Air Quality Index (AQI) and what is its purpose? (The EPA is a big part of this!)

The air quality index is a number used by government agencies (the EPA) to communicate to the public how polluted the air currently is or how polluted it is forecast to become. As the AQI increases, an increasingly large percentage of the population is likely to experience increasingly severe adverse health effects.

Explain how photochemical smog forms. Why is it a problem historically and currently in the US?

The first part of the process takes place during the day, in the presence of sunlight. When an abundance of nitrogen oxides are present in the atmosphere, with very few VOCs present, nitrogen dioxide (NO2) splits to form nitrogen oxide (NO) and a free oxygen atom (O). In the presence go energy inputs from sunlight, this free oxygen atom combines with diatomic oxygen (02) to form ozone (03). With abundant nitrogen dioxide and abundant sunlight, ozone can accumulate in the atmosphere..... (more stuff)

Is ozone always good? Explain.

There are many photochemical oxidants , and they are generally harmful to plant tissue, human respiratory tissue, and construction materials. Environmental scientists frequently focus on ozone, a secondary pollutant made up of three oxygen atoms bound together. It is harmful to both plants and animals and impairs respiratory function. So, no, it is not always good.

Are nitric acid and sulfuric acid primary or secondary pollutants? Why?

They are secondary pollutants.

How do the NAAQSs regulate anthropogenic emissions?

Through the National Ambient Air Quality Standards (NAAQS), the EPA periodically specifies concentration limits for each air pollutant. For each pollutant the NAAQS note a concentration that should not be exceeded over a specified time period.

Name a human activity that leads to the formation of tropospheric ozone?

Tropospheric ozone, (ground-level ozone) is found in the troposphere, which is the layer of air closest to the Earth's surface. The troposphere is the air from the ground to about 8 miles up into the atmosphere - it's the air we breathe. Ozone does not naturally occur at harmful levels in the troposphere. Our ground-level ozone problems are caused by human activities.

Name a secondary pollutant that is a component of photochemical smog and be able to describe how it forms as well as both an environmental and human health impact of that pollutant.

nitrogen oxides (NOx) combine in the presence of sunlight; NO2, which is formed as NO combines with oxygen in the air; and acid rain, which is formed when sulfur dioxide or nitrogen oxides react with water.