Oxides Research

Oxides Research

1. Assess evidence, which indicates increases in atmospheric concentration of oxides of sulfur and nitrogen.

Thorough collection of data, surveys, and tests from the 1950's indicate a rising trend in atmospheric concentrations of oxides of sulfur and nitrogen. An enhancement in funding, technological and information resources, has led to wider and more detailed analyses of oxides of sulfur and nitrogen concentrations, and as the diagrams indicate (see diagrams) there is a clear rise in these oxides.

Unfortunately, comprehensive statistics of various gases in the atmosphere only dates back to 50 years ago, therefore reducing numerical evidence available to scientists. However, complementary events, which have increased in regularity and severity, provide indirect evidence, which the increasing atmospheric concentrations of oxides of nitrogen and sulfur.

These indicators include:

* Mt Kilauea, Hawaii; released 350 000 tonnes of sulfur dioxide, annually since 1986

* Mt Pinatubo, Philippines; Spewed out 15-20 million tonnes of sulfur dioxide.

* Pea-Soup Fog, London; 4000 lives claimed due to fog, high in sulfur and other toxic chemicals concentration (0.4ppm). Caused by burning of coal, with high sulfur concentrations.

* High levels of nitrogen have contributed in increase of acid rain events.

* Nitrogen dioxide has been directly linked with the formation of photochemical smog

The increasing concentration of oxides of nitrogen can be more easily identified through the effects of acid rain. (as nitrogen oxides contribute heavily in the formation of acid rain, therefore an increase in regularity and severity of acid rain events, can be directly linked to large quantities of nitrogen oxides :

* Formation of precipitation such as fog and snow, with a pH of below 5.6.

* Effect on vegetation, in acid rain effected regions (see acid rain)

* Effect on the low buffering fresh water waterways.

* Acidic pH levels in soil.

* Deterioration of buildings and monuments.

Of course, these are just a few of the general indicators of acid rain (i.e. nitrogen oxides) and must be further investigated by scientists to confirm, their origins and use as evidence to support the increasing concentrations of nitrogen oxides.

Oxides of sulfur and nitrogen

In most large cities the annual average concentration of SO2 and NO2 is about 0.01 ppm each. This is 10 times the value for clean air, but it is not harmful.

Since the industrial revolution (early 1800s), SO2 emissions increased greatly due to the burning of coal (luckily Australian coal has a low percentage of sulfur 0.5%- 6%) unlike China etc. Air quality has decreased, indicated by nasty pollution events.

The fitting of gas absorbers onto factory flues helped to curb such emissions. But because SO2 and NO2 are washed out of the atmosphere by rain, there appears to not have been any significant build-up of their concentrations over the last century (unlike CO2 and 30% increase and NO, which has increased by an even greater percentage).

However, it is difficult to be sure about SO2 and NO2 because there is a lack of reliable data prior to 1950. It has only been in the last few decades that we have been able to mention concentrations of these gases below 0.1ppm. It is however interesting to note that even though concentrations of oxides of nitrogen (a contributor to photochemical smog) first became a problem in the 1960s, and the consequent introduction of emission controls on motorcars, which decreased the problem.

But cities are growing and there are more cars then ever. Thus to a large extent this has cancelled out further benefits of increasingly stringent controls.

SO2 will always form from volcanic eruptions. Oxides of nitrogen will always form in the atmosphere by nitrogen and oxygen and lightening reactions. More research is required into collating and summarizing old events prior to the 1800s such as fish deaths, damage to pine forests or erosion of marble/limestone (all due to acid rain). Must also be noted that the heat from cities is creating more thunderstorms, which means more oxides of nitrogen would be produced.

2. Summarize the industrial origins of sulfur dioxide and oxides of nitrogen AND evaluate reasons for concern about their release into the environment.

Sulfur dioxide and NO2 are pollutants that Corm in localised industrial areas such as big cities (with industry, power generation and many vehicles) and mining towns (SO, from roasting ores). They do not spread out globally because natural processes remove them from the air.

When these oxides disperse through larger volumes of air, they dissolve in water droplets (rain) and so are washed out of the atmosphere by rain.

Sulfur dioxide reacts to Corm sulfurous acid:

SO2(g) + H2O(l) --> H2SO4(aq)

In water droplets various other impurities in air catalyse the conversion of sulfurous acid to Sulfuric acid:

2H2S03(aq) + O2(g) --> H2SO4(aq) (with catalyst)

Sulfuric acid is also soluble in water and so it is removed from the atmosphere by rain. Similarly, nitrogen dioxide reacts with water to form a mixture of nitrous and nitric acids:

2N02(g) + H2O(l) ---> HNO2(aq) + HNO3(aq)

Nitrous acid in solution is catalytically oxidised to nitric acid:

2HN02(aq) + O2(g) ---> 2HNO3(aq) (with catalyst)

Again nitric acid is soluble in water and so is washed our of the atmosphere by rain.

After the Industrial Revolution of the earl- 1800s there was a great increase in emissions of sulfur dioxide (and particulates) to the air in the growing industrial cities (mainly from burning coal and extracting metals). Air quality deteriorated significantly - until about the 1950s and 60s when a series of nasty pollution episodes in London and the northeast of the USA caused many deaths. This led to the introduction of regulations to control emissions from factories and these caused a dramatic improvement