Changes in airborne pollen concentrations in Delhi, India

In order to find the qualitative and quantitative changes in airborne pollen concentrations in Delhi metropolis area an aerobiological survey was undertaken from September 1990 to August 1997. Air samples were collected daily using a Rotorod Aeroallergen Sampler at 10 m above the ground level. Ninety-four pollen types were recorded and the major contributors include Morus , Cannabis , Chenopod/Amaranth, Prosopis , Artemisia , and Eucalyptus . Ten pollen types contributed 90% of the total pollen load. Two major pollen seasons were recorded each year (February-April and September-November), although pollen grains in low frequency were recorded throughout the whole year. A significant reduction in pollen concentration was observed in subsequent years. The number of Morus , Cannabis , Prosopis , and Artemisia pollen decreased considerably while the number of Ricinus communis pollen did not show any considerable change during the study period. It is suggested that the reduction in pollen numbers from 1990 to 1997 in Delhi is due to massive clearing of vegetation for developmental activities of the city.