Environmental Chemistry Test - 65

1. Photochemical smog consists of primary and secondary pollutants. Primary pollutants consist of nitrogen oxides and volatile organic compounds, whereas secondary pollutants consist of Peroxy acetyl nitrate and ozone.
2. Aromatic hydrocarbons containing two or more fused rings are called Polycyclic aromatic hydrocarbons. It is found that the number and position of certain groups such as methyl, hydroxide, cyanide, and methoxy in these compounds give rise to carcinogenicity.
3. IR active molecules such as $$HCl, CO,$$ and $$NO$$ absorb the radiation from the infrared region and causes global warming.
4. Dioxins are a group of chlorinated organic compounds that are formed in Waster Incineration.

The weedkiller 2,4,5-T contains significant levels of an impurity called dioxin which causes birth defects in human babies. 

This herbicide contained an equal mixture of two phenoxy acids, one of which produces an obligatory byproduct called 2,3,7,8-tetrachlorodibenzo-p-dioxin, otherwise known as TCDD or dioxin.

Green chemistry is that branch of chemistry in which chemicals of daily needs are produced by using such existing knowledge that neither use toxic chemicals nor emit such chemicals into the atmosphere. Thus, it helps in reducing the chemical hazads alongwith development activities.

Ozone formation is due to the photochemical reaction of oxygen atoms.

The ozone layer in the stratosphere is created by the interaction of the UV radiation from the sun and the oxygen. It is capable of absorbing the most damaging type of UV radiation called the UV-B. The ozone hole refers to the depletion of the ozone by the pollutants like CFCs, HCFCs and HFCs. The pollutants split up due to UV radiation and the nascent chlorine reacts with the ozone molecules to form the oxygen. Over Antarctica, the ozone is highly depleted and so the widest ozone hole is seen there. This is because of the presence of the stratospheric cloud in abundance.

Peroxyacyl nitrates are hazardous respiratory and eye irritants present in photochemical smog. They are nitrates produced by the reaction of oxides of nitrogen with unsaturated hydrocarbons such as aldehydes or other compounds present in atmospheric VOC's

Formation of PANs (CH₃COOONO₂)

Hydrocarbons + O₂ + NO₂ + light → CH₃COOONO₂

So, the correct option is 'Peroxy-acyl nitrates'.

The discovery of the ozone hole over Antarctica was done by British Antarctic Survey Scientist Farman, Gardiner and Shanklin and reported in the Nature journal in May 1985. The ozone hole is defined as the area in the atmosphere where the value of the ozone is less than 220 DU. Paul Crutzen, Mario Molina and Sherwood Rowland gave the observation of CFCs in degradation of the ozone.

Photochemical oxidants are the secondary pollutants that are formed when the primary pollutants like hydrocarbons, oxides of sulphur, oxides of nitrogen react with sunlight. The major products of this reaction include tropospheric ozone, peroxyacetyl nitrate and aldehydes. They also contribute to the formation of the photochemical smog.

The main cause of ozone depletion and the ozone hole is manufactured chemicals, especially manufactured halocarbon refrigerants, solvents, propellants and foam-blowing agents (chlorofluorocarbons (CFCs), HCFCs, halons), referred to as ozone-depleting substances (ODS). the United States National Academy of Sciences concluded that credible scientific evidence supported the ozone depletion hypothesis[59] a few countries, including the United States, Canada, Sweden, Denmark, and Norway, moved to eliminate the use of CFCs in aerosol spray cans. The United States banned the use of CFCs in aerosol cans in 1978.[60] The European Community rejected proposals to ban CFCs in aerosol sprays.

In the stratosphere of the atmosphere, the UV rays are concentrated and these react with the oxygen to produce the ozone. This ozone persists in the form of the ozone layer and acts as the absorbent for the UV rays. Ozone layer does not allow the UV-B and UV-C from hitting the earth's surface, thereby preventing the various harmful after effects. Sulphur dioxide, carbon monoxide and methane are the primary pollutants of air.