Plants are exposed to a variety of anthropogenic ga seous and liquid pollutants which change the cellul ar biochemistry of plants directly or indirectly leadi ng to reduced morphological growth. In this study w e tried to correlate the combined impact of 2, 4-D sodium salt and automobile exhaust on the foliar chlorophyll a nd ascorbic acid content of Cymbopogon martinii. Two sites 1: B .B.A.U. campus as control site (less polluted) and 2: NBRI campus at Sekandarbagh crossing (one of the busiest crossings of Lucknow City) were selected based on the vehicular density. Three concentrations viz. 30mg/l , 100mg/l and 300mg/l of 2,4-D sodium salt were giv en to the plants. It was observed that exposure to 2, 4-D so dium salt led to an increase in ascorbic acid conte nt from 4±1.0 μ g/g f.w.in T3 (30mg/l of 2, 4-D) to 16.83±1.76 μ g/ g f.w.in T5 (300mg/l of 2,4-D) at the control site and from 22.23±3.35 μ g/g f.w. in T3 to 38.20±1.31 μ g/g f.w.i n T5 at the polluted site. However, foliar pigment content decreased significantly which corroborated with the deterioration of other plant growth parameters lik e total photosynthetic area and stem girth. The ultra struc tural changes in foliar morphology revealed that th ese plants can be used as biomarkers for auto exhaust pollution.