What would most likely happen if airborne pollution blocked the sun's rays so significantly that only 5% of plants survived?

This would produce a mass extinction mainly due to the lack of primary producers  

Explanation:

Primary producers are autotrophs organisms capable of converting solar energy and inorganic compounds (such as, for example, water and carbon dioxide) into chemical energy and organic matter. Primary producers include algae, plants, and certain bacteria. These organisms are critical for sustaining trophic interactions by synthesizing and assimilating nutrients required to sustain the life of heterotrophic organisms. Consequently, an environmental disaster like described in this question would have devastating consequences on the next trophic levels in food chain by eliminating a major source of food for heterotrophic life.

i think its white blood cells

i hope this