The World Health Organisation (WHO) recommends the use of N95 respiratory masks or well-fitted standard surgical masks. The N95 mask has 95% filtration efficiency rate for Mycobacterium tuberculosis (particle size 0.3 micron). These masks are an effective and important part of the personal protective equipment (PPE) used for infectious agents, like SARS, bird flu or other viruses/infectious disease agents.
N95 masks filter out smaller particles than surgical masks do and can be used for longer, but are harder to breathe through. N95 masks with a exhalation vent are easier to breathe through than those without, but are considered unsuitable for people who have flu.
The N95 masks are manufactured and marketed by 3M and others as well, and should be available in most Indian cities. Please check with the company for availability issues.