Fog and haze, exactly what kind of mask?

Currently for sale on the market of the so-called "anti-smog masks" has three main categories:

First, gauze masks. The masks can filter out most of the dust and germs, but there is little protective effect of PM2.5.

Second, the activated carbon mask. This mask to add a layer of activated carbon adsorption, but it only works on isolating odors against anti-haze particles is ineffective.

Third, medical masks, including medical disposable facemasks and N95 respirators. Common disposable medical masks are generally non-woven material, has the effect of spray, moisture-proof, but filtering particulate matter results are unsatisfactory, and not suitable against PM2.5.

In contrast, N95 mask anti-haze effects better, poor ventilation, likely to cause breathing difficulties, prolonged hypoxia can occur, such as chest tightness and respiratory function in children, the elderly and patients with cardiovascular disease should not be worn for a long time.