Fig. S1. Position and handling of samplers while travelling in different modes of transportation (a) Car, (b) Motor Bike and (c) Bus. Fig. S2. Stretches sampled for PM2.5 and NO2. Fig. S3. Representation of number of respondents for (a) Mode of transportation and for (b) Distance travelled. Numerous government institutions, Industrial establishments that use of heavy vehicles and gateway to North of Tamil Nadu Dominant vehicle type – Bus and heavy vehicles Numerous commercial and Educational Numerous commercial establishments, and government Gateway to South of establishments, two Tamil Nadu (high universities (IITM and usage of busses) ANNA University), Gateway to OMR (IT Dominant vehicle type HIGHWAY) – Bus and heavy vehicles Dominant vehicle type – Bus and motorbike Fig. S4. Zones of Chennai. Fig. S5. Concentration of PM2.5 and NO2 during diffirent time periods on three modes of transportation. Table S1. Stretch Characteristics and Travel Time Details of Sampling PREVALENT MODE OF TRANSPORTATION STRETCH / MAXIMUM TRAVEL MINIMUM TRAVEL AVERAGE TRAVEL DISTANCE MORNING EVENING TIME (MINS) TIME (MINS) TIME (MINS) Stretch BETWEEN PEAK OFF PEAK PEAK No STRETCH HOURS HOURS HOURS BIKE CAR BUS BIKE CAR BUS BIKE CAR BUS Thiruvanmiyur to Poonamallee 1 (22Kms) Bus/Freight Bus/Freight Bus/Freight 89 167 187 26 55 89 58 111 138 Thiruvanmiyur to Broadway 2 (20Kms) Bike Bike Bike 68 121 140 31 45 98 50 83 119 Thiruvanmiyur to Tambaram 3 (21Kms) Bus/Freight Bus/Freight Bus/Freight 57 104 124 21 77 98 39 91 111 Thiruvanmiyur to Thiruvottiyur (24kms) Bus/Freight Bus/Freight Bus/Freight 100 187 210 45 90 112 73 139 161 4 Thiruvanmiyur to Perambur 5 (21Kms) Bike Bike Bike 98 114 145 22 78 87 60 96 116 Thiruvanmiyur to Avadi 6 (33Kms) Bus/Freight Bus/Freight Bus/Freight 121 182 208 61 98 121 91 140 165 Table S2. Zones of the Road Stretches Studied Stretch No Stretch Direction from Zone of Chennai Start point Destination Thiruvanmiyur S1 Thiruvanmiyur Ponamallee West South S2 Thiruvanmiyur Broadway North North S3 Thiruvanmiyur Tambaram South South S4 Thiruvanmiyur Thiruvottiyur North Northern suburb S5 Thiruvanmiyur Perambur West North S6 Thiruvanmiyur Avadi West North .