Air pollution tolerance Index is been used in studies like Green belt development, traffic noise reduction and Pollution mitigation at roadside sites and around industries.

1. APTI
Air Pollution Tolerance Index
Sandeep Kumar
Centre for Environment Science and Climate Resilient
Agriculture
ICAR-Indian Agricultural Research Institute
New Delhi 110012

2. A large number of plant parameters have been used for this purpose,
including
 visible foliar injury (Davis and Wilhour, 1976),
 leaf conductance (Winner, 1981),
 membrane permeability (Farooq and Beg, 1980),
 ascorbic acid (Keller and Schwager, 1977),
 relative water content (Rat, 1979),
 chlorophyll content (Bell and Mudd, 1976),
 leaf-extract pH (Chaudhary and Rao, 1977) and
 peroxidase activity (Eckert and Houston, 1982).

3.  The sensitivity of plants and tolerance parameters
varies with air pollutant level at the study area.
 Air pollution tolerance Index is been used in studies like
Green belt development, traffic noise reduction and
Pollution mitigation at roadside sites and around
industries.

4. • The Air pollution tolerance index is an
empirical relation which evaluates the
tolerance level of plant species towards
air pollution from leaf biochemical
parameters such as Leaf extract pH,
relative water content of the leaf,
ascorbic acid and total chlorophyll.
• The APTI is formulated by Singh and Rao
(1991).

5. • Ascorbic acid, through its reducing power,
protects chloroplasts against SO2-induced
H202, 02- and OH accumulation, and thus
protects the enzymes of the CO 2 fixation
cycle and chlorophyll from inactivation
(Tanaka et al., 1982).
• Together with leaf pH, it plays a significant
role in determining the SO2-sensitivity of
plants (Chaudhary and Rao, 1977; Rao,
1979).

6. • Its reducing power is more at higher
and less at lower pH values. Thus, it
may be possible that ascorbic acid
protects chloroplasts and chlorophyll
functions from pollutants through its
pH-dependent reducing power.
• Thus, the A(T+ P) part of the formula
represents the potential of chloroplast
to combat pollutants after their entry
inside the plant.

7. • The addition of RWC to A(T+ P) shows
the capacity of the cell membrane to
maintain its permeability under polluted
conditions.
• Thus, this combination of four
parameters is suggested as
representing the best index of the
susceptibility levels of plants under
field conditions.

8. The categorization of the plant species is
based on method of Singh and Rao (1983). The
formula of APTI is given as
APTI =
Where,
A = ascorbic acid content (mg/g)
T = total Chlorophyll (mg/g)
P = pH of leaf extract
R =relative water content of leaf (%)

9. The plants are categorized according to APTI
values
plants Sensitive intermediat
e
Moderately
tolerant
Tolerant
Deciduous ˂ 14 15 - 19 20 - 24 ˃ 24
Evergreen ˂ 12 13 - 16 17 - 20 ˃ 20
Herbs ˂ 10 11 - 14 15 - 18 ˃ 18
Crop ˂ 16 17 - 29 - ˃ 29

10. Relative water content
Relative turgidity is a direct measure of deficit in leaves. Relative water
content indicates the capacity of the cell membrane to maintain its
permeability under polluted conditions. Relative water content was
estimated by Bars and Weatherley’s.
RWC =
Where,
FW = Fresh weight
DW = Dry weight
TW = Turgid weight
Fresh weight was obtained by weighing the fresh leaves. The leaves
were then immersed in water over night, blotted dry and then weighed
to get the turgid weight. The leaves were than dried overnight in an
oven at 70°C and reweighed to obtain the dry weight.

11. Leaf extract pH
 pH of the leaf extract signifies the tolerant capacity of the
leaf species.
 Studies have shown that decline of pH during the
presence of acidic pollutant, pH of leaf is found lowered in
sensitive species than tolerant plants. Higher level of pH
in leaf extract indicates that the plants are tolerant under
polluted conditions.
 pH plays an important role in signifying the condition of
plants with respect to the study area. pH is estimated
followed by Singh and Rao’s procedure.
 2g of the fresh leaves was homogenized in 20ml
deionised water.

12. Ascorbic acid
• Take 5 ml of working standard into a 100 ml conical flask.
• Add 10 ml of 4% oxalic acid and titrate against the dye (V1
ml).
• End point is appeared as pink color which persists for a few
minutes.
• The amount of the dye consumed is equivalent to the amount
of ascorbic acid.
• Extract the sample (0.5 to 5 g, depending on sample) in 4%
oxalic acid and make up to a known volume (100 ml) and
centrifuge (5000 rpm for 20 min).
• Take out 5 ml of this supernatant and add 10 ml of 4% oxalic
acid and titrate against the dye (V2 ml).
Amount of ascorbic acid (mg/100g sample) =
Where,
V1 is volume of dye during first titration (ml)
V2 is volume of dye during first titration (ml)

13. Total Chlorophyll content
 Take 1g of finely cut and well mixed samples of leaves into a clean mortar and
pestle.
 Grind the leaves with addition of 20 ml 80% acetone until the color of leaves
disappear (volume of acetone can vary).
 Centrifuge at 5000 rpm for 5 min and transfer the supernatant to a 100 ml
volumetric flask.
 Make up volume to 100 ml with 80% acetone.
 Read the absorbance of the solution at 645 and 663nm against the solvent blank
(80% acetone)
Chlorophyll a (mg/g sample) =
Chlorophyll b (mg/g sample) =
Total chlorophyll (mg/g sample) =
Where,
A= Absorbance at specific wavelength
V= Final volume of chlorophyll extract in 80% acetone (ml)
W= Fresh weight of the tissue extracted (gm)

14. धन्यवाद