Particulate is the term given to the minute particles of solid or semi solid material dispersed in the atmosphere. It is this dirt in the air, that is visible as a 'Brown Cloud', haze or smog. Particulates that range in size from less than 0.1 micrometre (µm) upto approximately 45 µm are designated as dust or 'Total Suspended Particulates. Particulates larger than that range tends to settle as dust and do not remain suspended, except during high winds.

Figure 4 Disposition of Particulate Matter (PM) in the Respiratory system (Richard Wilson, Harvard Press,1996)

The human nostrils filter out 99% of the inhaled large and medium sized particles (Table 4). The rest may enter the windpipe and lungs (Fig. 4) where some inhalable particulates cling to protective mucous and are removed. Some of the smallest particles, called respirable particulates may tend to be deposited in the alveoli (tiny air sacs in the lungs). In the lungs, particulates slow down the exchange of oxygen with carbon dioxide in the blood, causing shortness of breath. The heart gets strained, because it works harder to compensate for oxygen loss. Usually, people most sensitive to these conditions have respiratory diseases like emphysema, bronchitis, asthma or heart problems. Particles themselves may be poisonous if inhaled, damaging remote organs like the kidneys or liver. Swallowed mucous that is laden with hazardous particulate matter may damage the stomach.

In addition, particulates may be the carriers of hazardous liquid or gaseous substances. Sulphur dioxide, a major air pollutant, is frequently absorbed by particulates and can react with moisture to form sulphates. Sulphates react with moisture in the air or in the respiratory tract to form a corrosive liquid (sulphuric acid) that irritates delicate membranes and slow down the body's ability to remove harmful bacteria, increasing the possibility of infection.

3.1 Health effects of Ambient Air particulates

A study conducted in the United States during 1994 indicates that increase of PM₁₀ (particles less than 10 micrometer diameter) by 10 µg/m³ on daily basis results in increase in mortality rates by 1.0 - 3.2%. The corresponding increase in hospital admissions is 1-2%. United Kingdom study concludes that PM₁₀ contributes to 1.9% more deaths and additional hospital emissions. In another study, it was found that the total mortality is observed to increase by approximately 1.0% per 10 µg/m³ of PM₁₀, while about 1.4% cardio-vascular mortality has been observed per 10 µg/m³ increase in PM₁₀. The hospital admissions and emergency department visit increases by 0.8% and 1.0% per 10 µg/m³ increase of PM₁₀ respectively.

Table 3 Dust and Occupational Health Effects

3.2 Particulate Deposition And Host Defense Mechanisms

When airborne particles come in contact with the wall of the conducting airway or a respiratory unit, they tend to be deposited and do not become airborne again. This constitutes deposition and can be achieved in one of the following four ways.

Most compact particles, larger than 20 µm aerodynamic diameter and about half of these of 5 µm aerodynamic diameter are filtered with the nose during breathing at rest. However there is wide variation in the efficiency of this among apparently normal subjects. Moreover conditions which favour mouth breathing (e.g. high ventilation rates and obstructive disease of the nasal airways) will cause large particles to bypass this filter. Alveolar deposition is appreciable at particulate diameter of between 2 µm and 4 µm. During regular breathing at rest, only about 10% of compact particles of 0.5 to 1 µ diameter tend to be deposited in the lung (alveoli), of which the bulk is exhaled.

3.3 Effects of Kolkata’s Air Pollution on Adult Population

3.3.1 Respiratory Symptoms

A survey was conducted by Chitranjan Cancer Research Institute, Kolkata on 1310 individuals from Kolkata and 200 from rural West Bengal through questionnaire and clinical examination concerning respiratory ailments. Symptoms related to problems in the upper respiratory tract were found in 41.3% of urban and 13.5% of rural subjects, while lower respiratory tract symptoms were found in 47.8% of urban people in contrast to 35% of rural controls. Respiratory symptoms were most frequent during winter when the pollution level of the city with respect to Respirable Particulate Matter (RPM) was highest. However, the frequency of the symptoms during monsoon was greater than that of summer perhaps due to proliferation of micro-organisms from elevated humidity during monsoon. Assessment of lung finction by spirometry in selected urban groups- street hawkers, garage workers, office employees and students reveal that 47% individuals showed impaired lung function, and persons with restrictive (26.5%), obstructive (10.2%) or both types of respiratory disorders (10.2%) were found. The percentage of individuals with impaired lung function (47%) correlates well with the frequency of lower respiratory (47.8%) in urban people. Thus chronic inhalation of Kolkata’s air causes decline in lung function in a significant percentage of inhabitants of the city.

3.3.2 Marked Rise in Alveolar Macrophages: Biomarker of Pollution Effect

Alveolar Macrophages (AM) are a group of phagocytic cell which is the ultimate defense mechanism against inhaled pollutants. They engulf the pollutants and tries to marginalize them. Presence of large number of AM in deep sputum indicates the exposure of the individual to high particulate pollution. Alveolar Macrophage counts were made among the rural subjects and urban population of Kolkata. Compared to 3.4 AM per high power field (hpf,400x magnification) in rural population, the mean AM in urban subjects was 22.7. Hence residents of Kolkata had 6.7 times more AM than their rural counterparts. High or alarming AM count (10-40 or more AM/hpf) was observed in over 90% of urban smokers compared to 60% of nonsmokers. AM also showed a direct relationship with the degree of exposure to urban air pollution. Persons exposed to high level of vehicular emission like traffic policeman, drivers , garage workers and street hawkers of Kolkata had a mean value of 27.7AM/hpf (Figure 7) compared to 18.3 AM/hpfin relatively less exposed office employees, housewives and students. Thus the AM count in sputum appears to be good biological marker of air pollution effect on airways.

3.3.3 Variation of RSPM and Mortality Rate in Kolkata

Studies carried out by West Bengal Pollution Control Board on the RSPM concentration in Kolkata air indicate that the level of such killer particles remains very high during winter months especially in December and January. During April to October, the level remains within the permissible limit. RSPM levels between 1997 and 2000 have decreased steadily. The annual mortality rate in Kolkata shows a similar declining trend during the same period. Many countries have reported similar declining trend in RSPM levels with mortality rate (Figure 6). With Kolkata showing encouraging result in this regard, new action plan should be passed to reduce the RSPM levels in other parts of the country.