FACTORS AFFECTING PLANT SENSTIVITY TO AIR POLLUTANTS

Pollutant	Factor	Sensitivity	Comment
C2H4 pollution	Tissue age	Epinasty in immature leaves. Other symptoms on oldest leaves first.	Tissues with high natural C2H4 are more sensitive.
C2H4 pollution	High temperature	Sensitivity increased
C2H4 pollution	Other pollutants	Effects inhibited by high levels of SO2 or CO2
Cl2 pollution	Bright sunshine	Sensitivity increased
Cl2 pollution	Tissue age	Little effect; in conifers, current year’s needles most sensitive	Immature leaves tolerant in some species.
Cl2 pollution	Wet leaves	No effect
Cl2 pollution	Drought	Sensitivity decreased
Cl2 pollution	Low temperature	Sensitivity decreased in pines	Symptoms take longer to develop.
Cl2 pollution	Plat age	Seedling less sensitive than oleder plants
HCl pollution	Tissue age	Young, fully expanded leaves most sensitive	Immature leaves tolerant.
HCl pollution	Plant age	Seedlings less sensitive than mature plants	Older plants become more tolerant.
HCl pollution	High relat. Humidity	Sensitivity increased
HCl pollution	Ca-deficit	Sensitivity decreased	Effect shown for Nasturtium. May be different for other species.
HCl pollution	Ca-excess	Sensitivity increased	Effect shown for Nasturtium. May be different for other species.
HCl pollution	Cl-deficit	Sensitivity increased	Effect shown for Nasturtium. May be different for other species.
HCl pollution	Cl-excess	Sensitivity increased	Effect shown for Nasturtium. May be different for other species.
HCl pollution	Mg-deficit	Sensitivity increased
NH3 pollution	Concentration	Variable	Some conifers sensitive at moderate but tolerant at high levels.
NH3 pollution	Tissue age	Little effect
NH3 pollution	Darkness	Variable
NH3 pollution	Drought	Sensitivity decreased
NH3 pollution	Wet leaves	Sensitivity increased	Symptoms develop faster.
NOx pollution	Ca-excess	Sensitivity decreased	Opposite effect in some species.
NOx pollution	Tissue age	Immature leaves/needles most sensitive
NOx pollution	Cultivar	Highly variable; especially in gladiolus & tomato	In gladiolus, sensitivity related to flower colour
NOx pollution	High relat. humidity	Sensitivity increased
NOx pollution	Low temperature	Sensitivity decreased; symptom expression delayed
NOx pollution	Drought	Sensitivity decreased; symptoms induced in conifers needles previously exposed.	Sensitivity increased in some fruit trees.
NOx pollution	N-deficit	Sensitivity decreased	Opposite effect in some species.
NOx pollution	Ca-deficit	Sensitivity decreased	Opposite effect in some species.
NOx pollution	N-excess	Sensitivity decreased	Opposite effect in some species.
NOx pollution	P-excess	Sensitivity increased	Opposite effect in some species.
NOx pollution	Other pollutants	Interaction with SO2, NO2, O2 & hydrocarbons	Response varies with concentrations and relative proportions.
NOx pollution	K-deficit	Sensitivity increased	Opposite effect in some species.
O3 pollution	K-excess	Variable sensitivity
O3 pollution	N-excess	Variable sensitivity
O3 pollution	Plant age	Young plants most sensitive
O3 pollution	Tissue age	Intermediate leaves usually most sensitive
O3 pollution	Darkness	Sensitivity decreased	Plants grown in low light are more sensitive. High light during exposure increases injury.
O3 pollution	Wet leaves	Variable sensitivity
O3 pollution	Drought	Sensitivity decreased
O3 pollution	Other pollutants	Interactions with SO2, NO2, PAN & heavy metals	Response varies with species, concentration & relative proportions
O3 pollution	High soil salinity	Sensitivity decreased
O3 pollution	High relat. Humidity	Sensitivity increased
O3 pollution	S-excess	Sensitivity decreased
O3 pollution	N-deficit	Variable sensitivity
O3 pollution	P-deficit	Sensitivity decreased
O3 pollution	Low temperature	Sensitivity decreased	Sensitivity decreases again above 30 degree C. Response varies according to dose.
O3 pollution	K-deficit	Variable sensitivity
PAN pollution	High relat. Humidity	No effect
PAN pollution	Tissue age	Young, rapidly expanding leaves most sensitive	Sensitivity strongly affected by physiological age, results in bands of damage.
PAN pollution	Other pollutants	Interactions with O3 & SO2	Response varies with concentrations & pollutant.
PAN pollution	Drought	Sensitivity decreased
PAN pollution	Time of day	Sensitivity more in morning than after noon
PAN pollution	Darkness	Injury eliminated. Sensitivity increases with increased light intensity	Presence of light before, during and after exposure must for injury to occur.
PAN pollution	Low temperature	Injury decreased
PAN pollution	Plant age	Young plants more sensitive
SO2 pollution	Other pollutant	Interaction with O3, NO2, HF	Response varies with concentrations and relative proportions.
SO2 pollution	Time of day	More sensitivity when sugar content low	In many plants in the morning.
SO2 pollution	High relat. Humidity	Sensitivity increased
SO2 pollution	Drought	Sensitivity decreased
SO2 pollution	High wind	Sensitivity increased
SO2 pollution	Wet leaves	Variable; may increase
SO2 pollution	Darkness	Sensitivity decreased	Some plants e.g. Potato not closing stomata at night may be unaffected.
SO2 pollution	Low temperature	Sensitivity decreased	Susceptibility to frost injury increased by SO2 exposure
SO2 pollution	Plant age	Seedlings more sensitive than older plants
SO2 pollution	Season	Grasses more sensitive in winter; conifers more in April/May than in July/August	Not vry important for very short exposures.
SO2 pollution	N-deficit	Sensitivity decreased
SO2 pollution	S-deficit	Sensitivity decreased
SO2 pollution	P-deficit	Sensitivity decreased
SO2 pollution	N-excess	Sensitivity decreased
SO2 pollution	K-deficit	Sensitivity increased
SO2 pollution	S-excess	Sensitivity increased
SO2 pollution	Tissue age	Most in young, fully expanded leaves
SO2 pollution	Ca-deficit	Sensitivity increased

MINIMUM EXPOSURE TO AIR POLLUTANTS FOR PLANT INJURY

Plant name	Pollutant	ppm	hours	tolerance
Alder	HCl	6.00	4.00	Middle
Aster	HCl	9.00	0.40	Low
Barley	HCl	7.00	0.40	Very low
Bean	HCl	4.00	0.40	Very low
Beech	HCl	1000.00	1.00	Very high
Cherry	HCl	9.00	4.00	High
Chrysanthemum	HCl	9.00	3.00	High
Cornflower	HCl	20.00	0.40	Middle
Cosmos	HCl	9.00	0.40	Low
Douglas fir	HCl	10.00	4.00	High
Marigold	HCl	9.00	0.40	Low
Nasturtium	HCl	9.00	0.40	Low
Norway maple	HCl	7.00	4.00	High
Norway spruce	HCl	19.00	4.00	Very high
Oak	HCl	1000.00	1.00	Very high
Tomato	HCl	5.00	2.00	Low
Tulip tree	HCl	3.00	4.00	Low
Weymouth pine	HCl	8.00	4.00	High
Zinnia	HCl	9.00	0.40	Low
Annual poa	NH3	12.00	4.00	Middle
Buckwheat	NH3	16.60	4.00	Middle
Chickweed	NH3	12.00	4.00	Middle
Dandelion	NH3	12.00	4.00	Middle
Apple	SO2	0.40	6.00	Middle
Aspen	SO2	0.40	3.00	Middle
Barley	SO2	1.30	1.00	Very low
Bean	SO2	0.80	3.00	Low
Begonia	SO2	0.30	1.00	Very low
Broad bean	SO2	2.00	4.00	High
Broccoli	SO2	0.30	4.00	Low
Buckwheat	SO2	0.70	1.00	Very low
Cabbage	SO2	1.00	4.00	Low
Chrysanthemum	SO2	2.50	3.00	Very high
Cocksfoot	SO2	3.10	6.00	Very high
Cucumber	SO2	0.80	4.00	Low
Dandelion	SO2	2.00	4.00	High
Douglas fir	SO2	0.70	4.50	Middle
French marigold	SO2	2.00	2.00	High
Geranium	SO2	2.00	2.00	High
Ginkgo	SO2	2.80	3.00	Very high
Gladiolus	SO2	0.50	8.00	Middle
Iris	SO2	0.50	8.00	Middle
Italian ryegrass	SO2	1.90	6.00	High
Larch	SO2	0.30	8.00	Low
Lettuce	SO2	1.00	2.00	Low
Locust tree	SO2	2.00	4.00	High
Lucerne	SO2	0.10	4.00	Low
Lilac	SO2	0.30	6.00	Middle
Tomato	NH3	8.30	5.00	Low
White clover	NH3	100.00	0.10	Middle
African marigold	C2H4	0.01	20.00	Low
Cattleya orchid	C2H4	0.00	24.00	Very low
Aspen	O3	0.15	2.00	Low
Bean	O3	0.06	8.00	Low
Begonia	O3	0.13	3.00	Low
Bindweed	O3	0.20	4.00	Low
Apple	C2H4	0.01	48.00	Middle
Buckwheat	C2H4	0.05	48.00	Middle
Carnation	C2H4	0.10	6.00	Low
Chrysanthemum	C2H4	1.00	9.00	High
Cucumber	C2H4	100.00	6.00	Very high
Fat hen	C2H4	0.05	48.00	Middle
Forsythia	C2H4	0.70	20.00	High
Narcissus	C2H4	0.40	1.00	Very low
Pepper	C2H4	0.10	8.00	Low
Rose	C2H4	10.00	24.00	Very high
Snapdragon	C2H4	0.50	1.00	Very low
Strawberry	C2H4	1.00	24.00	High
Sunflower	C2H4	0.05	48.00	Middle
Tomato	C2H4	1.00	24.00	Middle
Tulip	C2H4	0.40	1.00	Very low
Norway maple	SO2	2.50	3.00	High
Oats	SO2	1.00	1.00	Low
Onion	SO2	1.00	4.00	Low
Pea	SO2	1.00	1.00	Low
Petunia	SO2	2.00	4.00	High
Pine	SO2	0.30	2.00	Low
Plantain	SO2	0.80	6.00	Middle
Poplar	SO2	2.00	4.00	High
Potato	SO2	4.20	1.00	Middle
Radish	SO2	0.50	1.00	Low
Red fescue	SO2	1.20	6.00	Middle
Rose	SO2	0.70	6.00	Middle
Rye	SO2	0.70	3.00	Low
Ryegrass	SO2	1.00	6.00	Low
Fat hen	NH3	12.00	4.00	Middle
Lettuce	NH3	2.00	24.00	Low
Ryegrass	NH3	100.00	0.20	Middle
Smooth-stalk meadow grass	NH3	12.00	4.00	Middle
Silver birch	SO2	0.90	2.00	Low
Smooth-stalk meadow grass	SO2	0.20	2.00	Low
Snapdragon	SO2	4.00	2.00	High
Spruce	SO2	3.00	6.00	Very high
Spinach	SO2	1.00	4.00	Low
Sweet pea	SO2	0.80	3.00	Low
Swiss chard	SO2	1.00	1.00	Low
Timothy	SO2	0.80	1.00	Low
Tomato	SO2	0.50	4.00	Low
Turnip	SO2	1.00	2.00	Low
Wheat	SO2	0.80	1.00	Low
Annual poa	HF	0.10	4.00	Low
Apple	HF	0.40	4.50	Middle
Azalea	HF	0.10	48.00	High
Bean	HF	0.70	2.30	Middle
Buckwheat	HF	0.70	2.30	Middle
Celery	HF	0.10	48.00	High
Chickweed	HF	0.10	4.00	Low
Corn	HF	0.10	4.00	Low
Dandelion	HF	0.10	4.00	Low
Dock	HF	0.50	8.00	High
Fat hen	HF	0.10	4.00	Low
Gladiolus	HF	0.06	6.00	Very low
Iris	HF	0.50	8.00	High
Lucerne	HF	0.10	48.00	High
Nettle-leaved goosefoot	HF	0.10	4.00	Low
Norway spruce	HF	0.20	5.80	Low
Pine	HF	0.07	4.00	Very low
Polygonum	HF	0.50	8.00	High
Rose	HF	0.50	8.00	High
Smoot-stalk meadow grass	HF	0.10	4.00	Low
Sunflower	HF	0.10	4.00	Low
Tomato	HF	0.30	3.00	Low
Tulip	HF	0.50	8.00	High
Azalea	Nox	13.00	1.00	Middle
Awnless brome	Nox	4.00	0.50	Very low
Bean	Nox	6.00	2.00	Low
Beet	Nox	30.00	1.00	High
Begonia	Nox	16.00	0.50	Middle
Broccoli	Nox	16.00	0.50	Middle
Buckwheat	Nox	4.00	4.00	Low
Chrysanthemum	Nox	4.00	0.50	Very low
Corn	Nox	4.00	0.50	Very low
Cocksfoot	Nox	4.70	6.00	Low
Cucumber	Nox	6.00	2.00	Low
Erica heather	Nox	1000.00	1.00	Very high
Sunflower	NH3	3.00	4.00	Very low
Italian ryegrass	Nox	4.70	6.00	Low
Lettuce	Nox	30.00	1.00	High
Lucerne	Nox	6.00	8.00	Low
Oats	Nox	4.00	0.50	Very low
Pea	Nox	6.00	4.00	Low
Plantain	Nox	3.30	6.00	Low
Potato	Nox	30.00	1.00	High
Radish	Nox	4.00	0.50	Very low
Rape	Nox	30.00	1.00	High
Rye	Nox	30.00	1.00	High
Ryegrass	Nox	4.70	6.00	Low
Red fescue	Nox	4.70	6.00	Low
Smooth-stalk meadow grass	Nox	4.70	6.00	Low
Spinach	Nox	6.00	2.00	Low
Swiss chard	Nox	1.00	1.00	Very low
Timothy	Nox	4.70	6.00	Low
Tomato	Nox	8.00	1.00	Low
Wheat	Nox	5.00	0.50	Very low
Azalea	Cl2	0.80	4.00	Low
Azalea	Cl2	0.80	4.00	Middle
Bean	Cl2	1.30	0.50	Low
Begonia	Cl2	1.00	4.00	High
Buckwheat	Cl2	0.50	1.00	Low
Carnation	Cl2	0.50	4.00	Middle
Clover	Cl2	35.00	2.00	Middle
Corn	Cl2	0.10	4.00	Very low
Cucumber	Cl2	0.50	4.00	Middle
Dahlia	Cl2	0.50	4.00	Middle
Dandelion	Cl2	0.50	4.00	Middle
Fat hen	Cl2	1.00	4.00	High
Geranium	Cl2	0.80	4.00	High
Lucerne	Cl2	0.10	2.00	Very low
Maple	Cl2	0.10	4.00	Very low
Nasturtium	Cl2	0.50	4.00	Middle
Onion	Cl2	0.80	4.00	High
Petunia	Cl2	0.10	4.00	Very low
Pine	Cl2	1.00	3.00	High
Polygonum	Cl2	1.00	4.00	High
Radish	Cl2	0.10	2.00	Very low
Rose	Cl2	1.00	0.50	Low
Ryegrass	Cl2	35.00	0.20	Middle
Squash	Cl2	0.80	4.00	High
Sunflower	Cl2	0.10	2.00	Very low
Tomato	Cl2	0.50	4.00	Middle
Zinnia	Cl2	0.10	4.00	Low
Buttercup	O3	0.20	4.00	Low
Chrysanthemum	O3	0.26	3.00	Low
Corn	O3	0.10	2.00	Low
Corsican pine	O3	0.25	4.00	Low
European larch	O3	0.25	4.00	Low
Grape	O3	0.40	4.00	Middle
Lettuce	O3	0.15	2.00	Low
Lucerne	O3	0.15	4.00	Low
Oats	O3	0.10	2.00	Very low
Pea	O3	0.10	2.00	Very low
Poplar	O3	0.18	4.00	Low
Radish	O3	0.08	2.00	Very low
Red clover	O3	0.15	4.00	Low
Scots pine	O3	0.25	8.00	Middle
Smooth-stalk meadow grass	O3	0.10	17.50	Very high
Spinach	O3	0.13	3.00	Low
Tobacco	O3	0.05	5.00	Very low
Common vetch	O3	0.20	4.00	Low
Weymouth pine	O3	0.07	4.00	Very low
Wheat	O3	0.23	3.00	Low
White clover	O3	0.15	4.00	Low
Bean	PAN	0.05	4.00	Low
Petunia	PAN	0.01	8.00	Low
Tomato	PAN	0.01	4.00	Low
Lettuce	PAN	0.05	12.00	High
Small nettle	PAN	0.05	35.00	Very high
Annual poa	PAN	0.05	42.00	Very high
Phalaenopsis orchid	C2H4	0.00	24.00	Very low