https://blog.gongquiz.com/2023/03/01/%ec%9c%a0%ec%9e%85%ea%b3%b5%ea%b8%b0-%ec%a4%91-%ec%97%bc%ec%86%8c%ea%b0%80%ec%8a%a4%ec%9d%98-%eb%86%8d%eb%8f%84%ea%b0%80-80000ppm%ec%9d%b4%ea%b3%a0-%ed%9d%a1%ec%88%98%ed%83%91%ec%9d%98-%ec%97%bc/