Figure 2: a) Sampling vehicle used on Kalimpong to Darjeeling route; b) Sampling vehicle used on Darjeeling to Siliguri route along the Teesta Valley; c, d) Position of air-filters in an engine of a motor car (white arrow) driving along the Darjeeling to Siliguri route; e) Collecting dust samples from the airfilter of a motor car; f) An air-filter of a motor car; g, h) Photographs of motor boats travelling around different islands of the Sundarbans (West Bengal); i) Red arrows indicate the position of the air-filter in an engine of motor boat; j) The inside view of an air-filter (red arrow) from a motor boat; k) An air-filter of motor boat; l, Collected soot samples from motor boats in plastic bag.