In the upper atmosphere, ozone can absorb the harmful ultra-violet (UV) radiation and has a positive effect by protecting life on the Earth’s surface. However at ground level, ozone produced by human activities causes problems. On calm, hot days in the summer, vehicle exhaust, gasoline vapors and other air pollutants collect over urban areas and interact with UV-B radiation to form ground-level ozone. At ground-level, ozone can cause serious eye, nose and respiratory problems in humans and animals, damage plants, field crops, and forests; and cause detrimental effects to many materials.

High concentrations of ground-level ozone can cause shortness of breath, coughing, wheezing, headaches, nausea, and eye and throat irritation. People who suffer from lung diseases like emphysema, bronchitis, pneumonia, asthma and colds have even more trouble breathing when the air is polluted. These effects can be worse in children, the elderly and exercising adults.

Children often play outside during hot, muggy summer afternoons. Their lungs are still developing, and they breathe more rapidly and inhale more air pollution per pound of body weight than adults. They also often breathe through their mouths, which means that the pollution bypasses the body’s first line of defense against pollution: the nose. On days when ozone smog levels are high, these factors put children at increased risk for respiratory problems.

On July 18, 1997, the U.S. Environmental Protection Agency (EPA) revised the National Ambient Air Quality Standard (NAAQS) for tropospheric ozone. Previously, the standard is exceeded when measured ozone concentrations are greater than 120 parts per billion (ppb) over a 1-hour period. Under the new standard, exceedances occur when measured ozone concentrations are greater than 80 ppb over an 8-hour period.

* A 1999 federal court ruling blocked implementation of the ozone 8-hour standard, which EPA proposed in 1997. EPA has asked the U.S. Supreme Court to reconsider that decision.

Based on EPA’s ozone 1-hour air quality standard, the non-attainment designations of ground-level ozone for the continental United States are presented in Figure 5. We can see most of the ozone polluted areas are concentrated in California and northeast America.

Everyone can help reduce the formation of ground-level ozone in order to achieve and maintain cleaner air! Here are some things you can do to reduce emissions of smog-producing chemicals during your daily activities:

• Keep your automobile well tuned and maintained.
• Follow the manufacturer’s instructions on routine maintenance, such as changing the oil and filters, and checking tire pressure and wheel alignment.
• Be careful not to spill gasoline when filling up your car or gasoline powered lawn and garden equipment.
• Limit driving by car pooling, consolidating trips, using public transportation, biking and walking.
• Participate in your local utility’s energy conservation programs.
• Use water-based or solvent free paints whenever possible and buy products that say “low VOC”.
• Seal containers of household cleaners, workshop chemicals and solvents, and garden chemicals to prevent VOCs from evaporating into the air.
• Limit barbecue emissions. Use and electric starter instead of lighter fluid to start charcoal fires, or use an electric, natural gas, or propane grill.
• Minimize your lawnmower emissions.
• Tune-up your lawn mower and use electric or hand-powered equipment if possible.

Generally, remote sensing is defined as “the science (and to some extent, art) of acquiring information about the Earth’s surface without actually being in contact with it. This is done by sensing and recording reflected or emitted energy and processing, analyzing, and applying that information”.

Figure 6 shows the different types of remote sensing. The two classes of sensors are passive (energy leading to radiation received comes from an external source, e.g., the Sun) and active (energy generated from within the sensor system, beamed outward, and the fraction returned is measured). Sensors can be non-imaging (measures the radiation received from all points in the sensed target, integrates this, and reports the result as an electrical signal strength) or imaging (the electrons released are used to excite or ionize a substance like silver (Ag) in film or to drive an image producing device like a TV or computer monitor or a cathode ray tube or oscilloscope; since the radiation is related to specific points in the target, the end result is an image [picture] or a raster display).

In much of remote sensing, the process involves an interaction between incident radiation and the targets of interest. This is exemplified by the use of imaging systems where the following seven elements are involved (Figure 7).

• Energy Source or Illumination (1) – the first requirement for remote sensing is to have an energy source which illuminates or provides electromagnetic energy to the target of interest.
• Radiation and the Atmosphere (2) – as the energy travels from its source to the target, it will come in contact with and interact with the atmosphere it passes through.
• Interaction with the Target (3) – once the energy makes its way to the target through the atmosphere, it interacts with the target depending on the properties of both the target and the radiation.
• Recording of Energy by the Sensor (4) – after the energy has been scattered by, or emitted from the target, we require a sensor (remote – not in contact with the target) to collect and record the electromagnetic radiation.
• Transmission, Reception, and Processing (5) – the energy recorded by the sensor has to be transmitted, often in electronic form, to a receiving and processing station where the data are processed into an image (hardcopy and/or digital).
• Interpretation and Analysis (6) – the processed image is interpreted, visually and/or digitally or electronically, to extract information about the target which was illuminated.
• Application (7) – the final element of the remote sensing process is achieved when we apply the information we have been able to extract from the imagery about the target in order to better understand it, reveal some new information, or assist in solving a particular problem.

Although remote sensing has been widely applied in Earth’s surface related research such as agriculture, forestry, and other environmental issues, it is rarely used in air pollution problem due to its limitation. Recently, multitemporal Landsat TM imagery were used to detect the land cover change and its relationship with ground-level ozone in southern New England. It open a perspective in remote sensing application in natural resources.

Figure 8 shows the areas in New England that are presently designated “non-attainment” for the one-hour ozone standard of 0.12 parts per million (ppm). Non-attainment areas for the one-hour ozone standard were classified as marginal, moderate, serious, severe, or extreme depending upon the severity of the air quality problem at the time of the Clean Air Act of 1990 passage. We can see that ground-level ozone presents a serious air quality problem in southern New England. The historically exceedances of 8-hour ozone standard in southern New England state: Connecticut, Massachusetts, and Rhode Island are presented in Figure 9.

Please note that the number of exceedances in a given year is very related to the number of days with elevated temperatures that year. The total number of ozone exceedance days in New England versus high temperature days (i.e., those with maximum temperatures greater than 90°F) for the years 1980 to 2000 (Figure 10).

In addition to the high temperature, ground-level ozone is also affected by other natural factors (e.g., sunshine, wind, and humidity) and human factors (land-use and land cover). Since the natural factors are largely beyond our control, the emission control of VOCs and NOx from human activities has been the major focus in the ground-level ozone reduction programs. Reducing gasoline and diesel engine use (NOx), plus curtailing activities involving VOCs, are common means to “shave the peaks” of ozone buildup and avoid exceeding the federal and state health-based standards for tropospheric ozone.

Land-use and land cover change, especially the urban sprawl, has been proven to play an important role in forming and distribution of ground-level ozone. Figure 11 shows the spatial variation of ground-level ozone in Connecticut and Rhode Island. The exceedance days for 1-hour ozone standard varied greatly in southeast New England. For example, East Hartford, CT only has 76 days exceeding the EPA standard from 1992 to 2000, while Stratford experienced over 200 days during the same time period.

The relationship between ground-level ozone and land cover types as well as land cover change was examined using multitemporal Landsat Thematic Mapper (TM) data. Ozone measurements from thirteen ozone monitoring stations in Connecticut and Rohde Island were used for the analysis. The monitoring stations were classified into different categories based on their locations and land cover characteristics (Figure 12). Comparisons of ozone concentrations and exceedances were made between land cover types and related to the dynamics of the land cover change. The results showed that ground-level ozone in southern New England region varied with land cover types and affected by land cover change. Strong correlation between ozone concentrations with land cover change indicates that the ozone problem is linked to overall environmental management and planning.

Over the South Pole, a dramatic thinning of the ozone layer occurs from September to November each year. Although the thinning is quite severe (up to 60 per cent depletion in recent years ), it is not actually a “hole” through the entire layer. This area of low concentrations in ozone or “hole” has been growing steadily and its edges now reach beyond the Antarctic continent to the tip of South America. Similar but less dramatic thinning of the ozone layer occurs over the North Pole each year as well.

“Ozone depletion” is the term commonly used to describe the diminishing of the Earth’s protective stratospheric ozone layer. To a great extent, it is the result of human activity. The leading cause of ozone depletion has proven to be chlorofluorocarbons (commonly called CFCs), a family of human-made chemicals which, until recently, were commonly used in air conditioners, refrigerators, foams, solvents and other products. CFCs are very stable chemicals that do not break down in the lower atmosphere. When released, they drift up into the stratosphere where they are broken down by ultraviolet radiation. This releases the chlorine that destroys ozone. A single atom of chlorine can destroy 100,000 or more molecules of ozone. Ozone depletion only stops when the chlorine randomly reacts with another molecule to form a long-lived, stable substance. At that point it is no longer free to react with ozone.