1. pungent /'pʌn(d)ʒ(ə)nt/
adj. （味道或气味）强烈的，刺激性的
e.g. The air is full of the pungent smell of incineration. 空气中弥漫着焚烧的刺鼻气味。
本季口语话题：describe a place you visited where air was polluted.
e.g. There were many cars, and the smell of exhaust fumes was so pungent and overwhelming that I could not even breathe. 
Syn. acrid （气味或味道）难闻的，刺激的
e.g. Clouds of acrid smoke of burning rubber brought tears to her eyes.
注：acrid 和 pungent 也可以用来描述讽刺或者刻薄的言论。
e.g. There is an acrid/ pungent tone to your remarks.
2. hazardous /'hæzədəs/
adj. 尤指对健康或安全有危险的，有危害的
e.g. hazardous waste 有害垃圾。
e.g. These are hazardous chemicals that can cause death if inhaled.
搭配：be hazardous to = be harmful to
e.g. Smoking can be hazardous to your health.
n. hazard 危险;危害
搭配：pose/ present a hazard to 对…造成危害。
e.g.  Fumes from the factory posed a serious hazard to the health of people living in the area.
3. smog /smɒg/
n. 属于blended word由smoke和fog组成，即雾霾。
e.g. As we flew into the airport, we could see a murky yellow smog hovering over the city.
注: murky 朦胧的
本句同样可以用在口语话题：a place where air was polluted.
adj. smoggy 
e.g. Children who live in areas that are highly polluted and smoggy are more likely to have asthma.
注: asthma 哮喘病
syn. haze 雾霾
e.g. It was a smoggy day and the buildings almost vanished behind a wall of haze.
最后学习两个与环境相关的 idioms.
1. A drop in the ocean. 沧海一粟
e.g. Some countries plant new forests but it's a drop in the ocean.
e.g. Unplugging unused appliances may be a drop in the ocean, but it would make a big difference if we all do that.
2. A hot potato 烫手山芋，棘手的问题。
e.g. Pollution in some countries might be ‘a hot potato’ due to the lack of an effective solution to waste management.