When my office moved to outer ring road, I was terrified of the pollution there - both dust and carbon emissions. I bought the decathlon mask. It was not easy to cycle hard with it. But works well for slow pedaling.
But I sometimes do carpentry and I have used the decathlon mask when I use drill or saw machines. It works so awesome!
But for commutes, I suffered for a month, bad bad cough and cold. I because vulnerable to this every now and then. Then I learnt a breathing technique wherein I narrow the throat at the point where we usually constrict during swallowing saliva. I narrow it enough and then open the nasal fully. I swallow saliva regular to ensure that the throat in the constricted area is wet and also to ensure that anything trapped there is swallowed to stomach regularly instead of getting stuck there forever or going into lungs. Breathing out can be fully open or however I want.
It has been 9 months of commute (2 days a week - 12 km one way) and it has worked wonders except that first one month when I tried with mask. As a bonus, even when I develop a bit of cold and runny nose, I use the same breathing technique and it does wonders there too.
My mask with the spare filters are now lying unused :-)