Introduction
Air quality in Indian
metropolitan cities is deteriorating very fast primarily due to Vehicular
pollution. Vehicular emission is a deadly cocktail of poisonous gases
and particles which affects the human beings, vegetation, agriculture
and buildings. Petrol driven vehicles are recognized today as a major
source of lead pollution in urban environment. In view of the rise in
the number of vehicles on roads, there is an increase in lead emission
from petrol driven vehicles. Realizing the gravity of problems, CPCB
carried out systematic study1&2 over a period of January,
1984 to April, 1987 in the city of Delhi, in order to study the lead
contamination of the roadside eco-system. Special attention was paid
towards curtailment of emission coming out of the vehicular exhaust,
introduction of unleaded petrol in four metro cities, a country-wide
wide phase-out programme for reduction of lead in petrol and sulphur
in diesel. Alongside, tightening of vehicular exhaust emission norms,
effective inspection and maintenance, improvement in public transport
and abatement of traffic management system are advocated by CPCB. Subsequently,
CPCB is monitoring lead in atmospheric environment of Delhi over years
since 1989 on monthly basis. However, concentrations of particle lead
as monitored by CPCB are generally showing an increasing trend.
Hazard of Lead
Pollution
Vehicular pollution
accounts for about 70% of air pollution in India’s metropolitan cities.
This figure was higher for Delhi, most of which is in close proximity
to the breathing zone. Airborne lead is typically present in vehicular
exhaust emission in the form of particles, which have diameter of less
than 1 p.m. and therefore may be transported to large distance with
a life time in the atmosphere between one and four weeks depending on
climatic factors. Inhalation of leaded aerosol from vehicular exhaust
is a potential source of body burden of lead. Pulmonary route of lead
exposure may account 40% of blood lead as 40% of inhaled lead is supposed
to be absorbed. However, 90% of the ingested lead is excreted out. In
human beings all organs contain some quantity of lead but almost 90%
is stored in the skeleton, while blood contains only 1% of lead. In
the blood almost 99% lead is associated with porphyrins. Exposure to
moderately low level of lead may produce abnormalities in the synthesis
of porphyrins inhibiting delta amino laevulinic acid (d-ALA) dehyrogenage.
As a consequence, blocking of haemoglobin occurs which result in increased
blood and urine level of d-ALA, which is also a diagnostic test for
acute and chronic lead poisoning.
Impact of Removing
Leading from Petrol on Blood Lead Levels
Low blood lead levels
were found in Tokyo, a city where all petrol has been free of lead since
1976. In contrast, petrol in Mexico City contained high lead content,
and people in Mexico City had high level of lead in blood. In USA, a
decline of petrol lead of 55% was accompanied by a fall of 37% in blood
lead level. These results are similar in the UK, where the lead reduction
in gasoline from 0.4 to 0.15 g/1 made in 1986 was followed by a 50%
reduction in atmospheric lead levels and a significant reduction in
blood lead levels.
Impact on Air
Environment due to Phase-out of Lead from Gasoline in India
Introduction of
lead free petrol in Delhi from. September l, 1998 has shown a reduction
in ambient particulate lead concentration in Delhi to the tune of 60%,
as monitored by CPCB. As a case study conducted by CPCB on impact of
unleaded petrol on urban environment is reflected from the table given
below:
Enrichment of
Lead in Fine Particulate Matter
A short-term preliminary
study conducted by CPCB has shown enrichment of lead in respirable particulate
matter at BSZ Marg (ITO Intersection), Delhi. Monthly mean value of
respirable particulate lead ranged between 339 and 581 ng/m', slightly
higher than the lead level in total suspended particulate matter (SPM).
However, this finding needs further investigation.
Vehicular Pollution
Control Strategies
The menace posed
by the vehicular population is further reinforced by sheer statistics.
Two-wheelers have grown in number accounting for 78.8% of all vehicles
in 1995 against 8.8% in 1951. The total number of vehicles in Delhi
(27.0 lacs or 2,700,000) was more than the number of vehicles in cities
of Mumbai (7.24 lacs), Calcutta (5.61 lacs) and Chennai (8-12 lacs)
in 1995. The total number of vehicles has grown up to more than 30 lacs
as on March 31, 1998.
Emissions from gasoline
(4-stroke spark ignited engine) vehicles are mainly from three sources,
i) crankcase blowby, which accounts for 20% all emission from vehicles;
ii) evaporative emissions, which accounts for another 20% of all emissions
from vehicles; and iii) exhaust emission (through tail pipe) which accounts
for 60% of all emissions of a 4-stroke spark ignited vehicle. In case
of 2-stroke gasoline engines, 3% emissions are due to evaporation while
rest is from exhaust.
Therefore, exhaust
emissions deserve special emphasis because it accounts for a larger
chunk of all pollution from gasoline based vehicles. Keeping this in
mind, CPCB has drawn an action plan at three stages: i) pre-combustion
stage, where the quality of the fuel can be upgraded; ii) combustion
stage, where engine modification and maintenance are required; and ii)
post combustion stage, where exhaust treatment devices, like catalytic
converters, are required.
Improvement in
Fuel Quality
Improving the quality
of fuel goes a long way in the abatement of vehicular pollution. With
this in mind, specification of motor gasoline (petrol) and diesel recommended
by CPCB has been notified under the Environment (Protection) Act, 1986,
which limits lead levels to 0.15 gm/litre which was implemented in four
metros namely Mumbai. Delhi, Calcutta and Chennai from June, 1994. Unleaded
petrol (0.013 gm/litre lead) was introduced from April, 1995 on partial
basis in 4 metros and in full in Delhi from September l, 1998. Benzene
levels have been limited to 5% by volume in the gasoline which are to
be further reduced to 3% in metro cities by year 2000. Total lead free
petrol is planned to be used in all state capitals by April, 1999 and
by December, 2000 in the entire country.
Emission Standards
The exhaust emission
standards for idling CO emission have been prescribed for vehicles.
The Ministry of Surface Transport has notified the vehicular mass emission
standards, as recommended by CPCB through Ministry of Environment &
Forests. Further, the stringent exhaust emission standard for vehicles
has been notified for the year, 2000 AD.
Exhaust Treatment
In order to reduce
the tail pipe emissions, government. has made the fitting passenger
cars with catalytic converters mandatory from April, 1995 in four metros.
Catalytic converters convert CO, HC and NOx into harmless CO2,
H2O and N2. The efficiency of catalytic converter
varies from 60-90%.
Maintenance of
In-use Vehicles, and Other Measures
Regular inspection
and maintenance by authorized service centres will go a long way in
reducing the pollution load.. Proper inspection and maintenance programs
are widely used in other countries where it has been possible to reduce
about 30-40% of pollution load from old vehicles. Similarly, improvement
in design of engines including fuel injection system will enable the
automobiles to go beyond compliance of emission standards. Some alternative
fuels have been used or are being tried, particularly alcohol, CNG and
electricity which may be promising options for reducing vehicular pollution.
Recommendation
and Further Work
- Besides above
abatement and control strategies, proper and systematic management,
improved road conditions, mass rapid transport system (high speed
tram) should be introduced at the earliest.
- Trees like Euginea
(Jamun) along roadsides and Nerium (Kaner) between road dividers and
alongside should be grown. These plants absorb and accumulate maximum
lead from the atmosphere as studied by CPCB.
- Unauthorized
primary lead smelting units should be identified, and the units not
meeting the lead emission standard should be closed down.
- Studies on Benzene
in the urban environment and near petrol pumps should be initiated,
which require immediate attention. CPCB has already initiated work
on this line using five different techniques namely thermal desorption,
metal traps filled with Tenax TA, activated charcoal glass traps,
both using active sampling, standard passive sampling traps and subsequent
analysis using capillary GC-FID, instant measurement with portable
GC-PID and Indicator tubes. Methods are being standardized for selection
and use in Indian conditions (both indicative and analytical methods).
- Benzene concentration
in motor gasoline has been prescribed as 3% (V/V) to be achieved by
all refineries by year, 2000 AD. Also CPCB is presently working on
an auto oil programme and is planning to reduce Benzene level to 1%
(V/V) from the year, 2005. To meet the 3% Benzene level, the refineries
in India are going through the catalytic reformer route to achieve
the standard.
References
- CPCB (1986);
"Impact of Auto exhaust lead pollution on vegetation in UT of Delhi";
Report No. EIAS/1/1985-86.
- CPCB (1987);
"Impact of Auto exhaust lead pollution on vegetation in UT of Delhi";
Report No. EIAS/2/1986-87.
- CPCB (1992);
"Report on Tetraethyl lead in petrol & lead in exhaust from automobiles";
Report No. Probes/46/1992.
- WHO (1997); "Environmental
Health Criteria - 3 : Lead". 5. CPCB (1997); "CPCB News Letter"; Vol.
4 (iii).
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