Dibenzo-p-dioxins and dibenzofurans (PCDD/Fs) are generated in the combustion processes, many studies indicate that both municipal waste incinerators (MWIs) and the industrial activities containing combustion processes are important sources of PCDD/F emissions. Local studies indicate that dioxin in ambient air originates mainly from waste incineration processes. In addition to the waste incineration process, electric arc furnaces (EAFs) have been identified as major sources for PCDD/F emissions. Because of the oncoming policy of regulating PCDD/F emissions standard for EAFs in Taiwan, it is important to develop control technology for effectively reducing PCDD/F emissions from EAFs. Many studies on dioxin emissions from large-scale MWIs and EAFs will decrease, and it will be to stably control the emission concentration under the regulation limit. We will study on dioxin emissions from waste incinerating in ambient air. So we must study background of dioxin and some data about it. We sample dioxin in ambient air each season in Taipei, Taichung, Kaoshiung and Hulien. There four sampling places in the four citues.