The amount of pollen in the air is six times as much as last year.
The pollen is six times as bad this year as it was last year.
この場合、次のような言い方ができますよ。
ーThe amount of pollen in the air is six times as much as last year.
「空気中の花粉の量は去年の６倍です」
ーThe pollen is six times as bad this year as it was last year.
「今年は去年と比べて、花粉が６倍ひどい」
ご参考まで！
カナダ 
