The DCV Program - Environmental Crisis

Air Pollution and Its Effects

In the early agricultural ages of mankind, air pollution as we know it today simply did not exist. Manmade smoke usually originated from burning wood used for cooking his food, and keeping him warm or to light the night with. Oil was used in lamps and lanterns which (except as fire hazard) posed little health risk when used properly. These had hardly, if at all, any significant environmental impact.

Around the Middle Ages, the use of coal in cities such as London escalated and even as far back as the 16th Century, poor air quality in urban areas were documented. The Industrial Revolution of the 18th and 19th Centuries in the United Kingdom depended heavily on the use of coal as fuel. Factories located inside towns and cities used large amounts of coal. homes and residential buildings likewise used coal for heating and cooking. The smoke from these sources combined with fog resulted in smog (smoke + fog). The smog became so bad at times that transportation in those cities came to a halt. The dirtying effect of the air pollution on buildings were clearly noticeable but more than that, death rates increased. Their 1875 Public Health Act included a smoke abatement section in an attempt to reduce air pollution in urban areas. So, long before any formal “Clean Air Act” was even conceived, there were already moves to reduce air pollution through legislation.

The 1926 Smoke Abatement Act in the UK aimed at industries brought about a reduction of smog in urban areas. Although in the early part of the 20th Century, the use of coal was diminishing, air pollution from other sources like industrial fuel oil were taking its place. In 1952, the Great London Smog caused an additional 4.000 deaths in the city resulting in the Clean Air Acts of 1956 and 1968 which formed smokeless zones in urban areas and a tall chimney policy on factories followed by later legislation including the 1974 Control of Air Pollution Act.

In major cities around the world, it had been observed that air pollution levels were getting so high that on some days, it was dense enough to make entire buildings disappear from view. Actually, the increasing number of motor vehicles in urban areas was the problem, the smog that was being generated was not really caused so much by smoke but by a chemical reaction between motor vehicle emissions and sunlight, thus producing what is known as “photochemical smog”. In the 1980s, concern of the public health focused on the effects of lead poisoning as that was the time of leaded gasoline. Medical authorities connected the rising incidences of lung cancer with urban air pollution besides heavy tobacco use.

In the United States, landmark legislation includes the Air Pollution Control Act of 1955, the Clean Air Act of 1963, the Air Quality Act of 1967 and the Clean Air Act of 1970, the 1977 Amendments to the Clean Air Act of 1970 and the 1990 Amendments to the Clean Air Act of 1970.

In the Philippines, Republic Act No. 8749 or the Philippine Clean Air Act of 1999 was established which, as stated therein: “AN ACT PROVIDING FOR A COMPREHENSIVE AIR POLLUTION CONTROL POLICY AND FOR OTHER PURPOSES”. The Philippine Clean Air Act became law on June 1999. Its key features include the following:

• Identification and characterization of all airsheds in the country and establishment of multi-sectoral AQM (Air Quality Management) Boards for each airshed;
• Development of a national air quality management framework, and a fund to be earmarked for air quality management activities;
• Imposition of air quality management charges;
• Improvement in quality of gasoline and diesel and promotion of alternative, cleaner fuels.

In compliance to legislations such as the Clean Air Acts, tougher regulations are enforced on the automotive industry, cleaner fuel compositions have been introduced (leaded gasoline being phased out), stricter motor vehicle emission standards established, etc. Also, industries are putting much research and development into using cleaner fuels such as ethanol and hydrogen as well as hydrogen fuel cells which generate electrical power to propel the vehicle. Other clean sources of power generation are also in development. Emissions from factories are likewise regulated although enforcement of clean air legislation may vary from one country to another.

Acid Rain

In addition to the health risks posed by just breathing in the pollutants, another destructive phenomenon has been observed: Acid Rain. Acid rain is rain or any other form of precipitation that is unusually acidic. It has harmful effects on plants, aquatic animals and buildings. The extra acidity in rain comes from the reaction of primary air pollutants, primarily sulfur oxides and nitrogen oxides, with water in the air to form strong acids (like sulfuric and nitric acid). Acid rain has been shown to have adverse impacts on the ecosystem, the forests, freshwaters and soils, killing off insect and aquatic lifeforms as well as causing damage to buildings and having possible impacts on human health. Although acid rain was discovered in 1852, it wasn't until the late 1960s that scientists began widely observing and studying the phenomenon and heightened public awareness came only in the 1990s.

Acid rain is mostly caused by emissions of sulfur and nitrogen compounds which react in the atmosphere to produce acids. The principal cause of acid rain is sulfur and nitrogen compounds from human sources, such as electricity generation, factories and motor vehicles. Coal power plants are one of the most polluting. These chemicals can be carried hundreds of kilometers in the atmosphere before they are converted to acids and comes down with the rain. In the past, factories had short funnels to let out smoke, but this caused many immediate health problems; thus, factories now have longer smoke funnels. However, this causes pollutants to be carried farther, causing greater ecological damage.

To reduce acid rain, a number of international treaties on the long range transport of atmospheric pollutants have been agreed on, e.g. the Sulphur Emissions Reduction Protocol under the Convention on Long-Range Transboundary Air Pollution. The US Clean Air Act Amendments of 1990 also addressed this problem with new regulatory programs authorized for control of acid deposition (acid rain).

On the technical side, many coal-burning power plants such as those in the US use flue gas desulfurization (FGD) to remove sulphur-containing gases from their stack gases. An example of FGD is the wet scrubber which is commonly used in the U.S. and many other countries. A wet scrubber is basically a reaction tower equipped with a fan that extracts hot smoke stack gases from a power plant into the tower. Lime or limestone in slurry form is also injected into the tower to mix with the stack gases and combine with the sulphur dioxide present. The calcium carbonate of the limestone produces pH-neutral calcium sulfate that is physically removed from the scrubber. That is, the scrubber turns sulfur pollution into industrial sulfates. Automobile emissions control reduces the discharge of nitrogen oxides from motor vehicles.

Ozone Depletion

Ozone (O3) depletion describes two distinct, but related observations: a slow, steady decline of about 4 percent per decade in the total amount of ozone in the Earth's stratosphere since the late 1970s; and a much larger, but seasonal, decrease in stratospheric ozone over Earth's polar regions during the same period. The latter phenomenon is commonly referred to as the “ozone hole”. Ozone depletion is caused by the catalytic destruction of ozone by atomic chlorine and bromine. The main source of these halogen atoms in the stratosphere is the photodissociation of chlorofluorocarbon (CFC) compounds, commonly called freons, and of bromofluorocarbon compounds known as halons. These compounds are transported into the stratosphere after being emitted at the surface. CFCs and other contributory substances are commonly referred to as ozone-depleting substances (ODS).

Chlorofluorocarbons (CFCs) were invented in the 1920s. They were used in air conditioning/cooling units, as aerosol spray propellants prior to the 1980s, and in the cleaning processes of delicate electronic equipment. They also occur as by-products of some chemical processes. No significant natural sources have ever been identified for these compounds — their presence in the atmosphere is due almost entirely to human manufacture.

Very large volcanic eruptions can inject hydrogen chloride (HCl) directly into the stratosphere, but direct measurements have shown that their contribution is small compared to that of chlorine from CFCs. A similar erroneous assertion is that soluble halogen compounds from the volcanic plume of Mount Erebus on Ross Island, Antarctica was a major contributor to the Antarctic ozone hole.

The Antarctic ozone hole is an area of the Antarctic stratosphere in which the recent ozone levels have dropped to as low as 33% of their pre-1975 values. The ozone hole occurs during the Antarctic spring, from September to early December, as strong westerly winds start to circulate around the continent and create an atmospheric container. Within this "polar vortex", over 50% of the lower stratospheric ozone is destroyed during the Antarctic spring.

As explained above, the overall cause of ozone depletion is the presence of chlorine-containing source gases (primarily CFCs and related halocarbons). In the presence of UV light, these gases dissociate, releasing chlorine atoms, which then go on to catalyze ozone destruction. The Cl-catalyzed ozone depletion can take place in the gas phase, but it is greatly enhanced in the presence of polar stratospheric clouds (PSCs).

These polar stratospheric clouds form during winter, in the extreme cold. Polar winters are dark, consisting of 3 months without solar radiation (sunlight). Not only lack of sunlight contributes to a decrease in temperature but also the “polar vortex” traps and chills air. Temperatures hover around or below -80 °C. These low temperatures form cloud particles and are composed of either nitric acid or ice. Both types provide surfaces for chemical reactions that lead to ozone destruction. The role of sunlight in ozone depletion is the reason why the Antarctic ozone depletion is greatest during spring. During the Antarctic winter (summer in the Northern Hemisphere), even though PSCs are at their most abundant, there is no light over the pole to drive the chemical reactions. During the spring, however, the sun comes out, providing energy to drive photochemical reactions, and melt the polar stratospheric clouds, releasing the trapped compounds.

Most of the ozone that is destroyed is in the lower stratosphere, in contrast to the much smaller ozone depletion through homogeneous gas phase reactions, which occurs primarily in the upper stratosphere. Warming temperatures near the end of spring break up the vortex around mid-December. As warm, ozone-rich air flows in from lower latitudes, the PSCs are destroyed, the ozone depletion process shuts down, and the ozone hole heals – although not completely due to the increased levels of ODS over the years resulting in the hole gradually becoming larger as time passes.

Since the ozone layer prevents most harmful UVB wavelengths (270–315 nm) of ultraviolet (UV) light from passing through the Earth's atmosphere, observed and projected decreases in ozone have generated worldwide concern. Biological consequences such as increases in skin cancer, damage to plants, and reduction of plankton populations in the ocean's photic zone may result from the increased UV exposure due to ozone depletion.

After a 1976 report by the U.S. National Academy of Sciences concluded that credible scientific evidence supported the ozone depletion hypothesis, few countries, including the United States, Canada, Sweden, and Norway, moved to eliminate the use of CFCs in aerosol spray cans. In 1985, 20 nations, including most of the major CFC producers, signed the Vienna Convention which established a framework for negotiating international regulations on ozone-depleting substances. That same year, the discovery of the Antarctic ozone hole was announced, causing a revival in public attention to the issue. In 1987, representatives from 43 nations signed the Montreal Protocol. At Montreal, the participants agreed to freeze production of CFCs at 1986 levels and to reduce production by 50% by 1999. After series of scientific expeditions to the Antarctic produced convincing evidence that the ozone hole was indeed caused by chlorine and bromine from manmade halogens, the Montreal Protocol was strengthened at a 1990 meeting in London. The participants agreed to phase out CFCs and halons entirely (aside from a very small amount marked for certain "essential" uses, such as asthma inhalers ) by 2000. At a 1992 meeting in Copenhagen, the phase out date was moved up to 1996. Also, the US Clean Air Act Amendments of 1990 included provisions regarding stratospheric ozone protection.

Since the adoption and strengthening of the Montreal Protocol has led to reductions in the emissions of CFCs, atmospheric concentrations of the most significant compounds have been declining. Gradually, the ozone layer is regenerating as new quantities of ozone are formed in the atmosphere, but it will take years due to the presence of the ODS which will still be floating in the atmosphere for some time to come. It is expected complete recovery of the Antarctic ozone layer will not occur until the year 2050 or later. Work has suggested that a detectable (and statistically significant) recovery will not occur until around 2024, with ozone levels recovering to 1980 levels by around 2068.

Although they are often interlinked in the mass media, the connection between global warming and ozone depletion is not strong. There are some common grounds, for instance, the same carbon dioxide (CO2) radiative forcing* that produces near-surface global warming is expected to cool the stratosphere. This cooling (cooler stratospheric temperatures, more stratospheric clouds, more active chlorine), in turn, is expected to produce a relative increase in ozone depletion and the frequency of ozone holes.

*In climate science, radiative forcing is loosely defined as the change in net irradiance at the tropopause, a boundary region in the atmosphere between the troposphere and the stratosphere. Here, the air ceases to cool at -50°C (-58°F), and the air becomes almost completely dry. "Net irradiance" is the difference between the incoming radiation energy and the outgoing radiation energy in a given climate system.