The aroma of agarbatti spreads quickly once you burn it because the particles in the agarbatti move endlessly in all directions. Both, the air and aroma, have large intermolecular forces which is why the molecules of air scatter immediately once agarbatti is burned.
Intermolecular force for solids is high. Whereas low in gases. The smell of agarbatti spreads immediately because the molecules of air diffuses very fastly.
