air

atmosphere

background

boy

catastrophe

chemical

chimneys

china

choke

city

concept

contamination

cough

damage

danger

dirty

ecological

ecology

energy

environment

factory

gas

gasp

guy

hazard

headache

health

human

ill

illness

industrial

industry

infection

kid

male

man

mask

person

pipes

pollution

problem

protection

respirator

safe

safety

sick

smoke

smokestack

urban

warming