If you have asthma, high amounts of (blank) can make it worse.
greenhouse gasses
air pollution
air pressure

Air pollution is the answer. The substances in the air could be pollutants which can harm your airways which can be really harmful to an asthmatic. I personally know because i have asthma myself.
 
Hope I hepled :)

Humid continental climate is found in the interior of continents between the 30 and 60 degrees latitude, but usually above the 40 degree line.   40 degrees north of the equator means less direct sunlight and therefore less warmth.   this climate is mainly found in the northern hemisphere since there are no major landmasses in the southern hemisphere.  if you live in northern indiana, you know all about humid continental because that is the climate type you have!

Ihave no idea what the answer is