The project is directed by the Tainan Municipal Environmental Protection Bureau (EPB), from May 5, 2017 to May 4, 2018, to do environmental monitoring of hazardous air pollutants (HAPs) in the ambient atmosphere. The analytical items include volatile organic compounds (VOCs), aldehydes and ketones, polycyclic aromatic hydrocarbon compounds (PAHs), acid-base gases, dioxin and heavy metals, and monitoring of PM2.5 emissions from stationary sources. The purpose of this project is to collect the concentration information of HAPs in Tainan City, and to establish PM2.5 emission fingerprint database and its emission coefficient according to the pipeline sampling results. This project uses the test data to propose specific control targets, recommended control strategies and expected improvement benefits for air quality improvement in Tainan City.
The results of the four seasons monitoring of HAPs are shown as the following. The VOCs in the air, the highest concentration measured in the first season (March 2017) of methanol, measured separately in Xinying elementary school (XYES) and Zhongshan middle school (ZSMS), 22.4 ppb and 28.2 ppb, the test value is much lower than the olfactory threshold (3300 ppb). The aldehyde and ketone compounds in the air measured the highest concentration in the second season (November 2017) of formaldehyde (0.0291 ppm) in ZSMS. The test value was slightly higher than the olfactory threshold (2.70×10-2 ppm). The PAHs in the air measured the highest concentration (3.2×10-4 mg/m3) of Naphthalene in the fourth quarter (February 2018) at the ZSMS. The test value is lower than the olfactory threshold (5.2 mg/m3). The acid-base gas in the air measured the highest concentration of ammonia (0.077 ppm) in the fourth quarter (May 2018) in XYES. The test value is still lower than the olfactory threshold (1.5 ppm).
The monitoring of ambient Dioxin showed the highest concentration occurred in the third quarter (February 2018), and the lowest in the first season (August 2017), and the displayed concentration may vary with the season. The concentration of PCDD/Fs in the atmosphere in summer is lower than that in winter, which is the same with the research results in literatures. The measured highest concentration of 0.083 pg I-TEQ/m3 occurred in the third quarter (February, 2018) at Xinshi elementary school. All the test values were all within the monitoring range of the national air quality monitoring station 0.001~0.255 pg I-TEQ/m3). The PCDD/Fs of each monitoring site accounted for a high proportion of PCDFs. The literature pointed out that if PCDD/Fs is generated by PAHs, PCDFs are dominant, and 2,3,4,7,8-pentachlorofuran (2,3,4,7,8-PeCDF) is the main characteristic species, which the sources were sintering plant, electric arc furnace and aluminum secondary smelting, etc., The ratio of PCDDs to PCDFs (PCDDs/PCDFs) of each station was less than 1, indicating that the Dioxin species mainly derived from the De Novo mechanism.
The results of heavy metal monitoring in the air showed that the elements are mainly aluminum (Al), barium (Ba), manganese (Mn), cobalt (Co) and other common crust elements. The concentration of heavy metal in PM2.5 showed no obvious seasonal change. Among them, the iron (Fe) concentration of 180 ng/m3 measured by Jianan University of Pharmacy in the first season (November 2017) was the highest. The highest concentration of heavy metal in PM10 was 980 ng/m3 aluminum (Al), measured at Longtian elementary school in the first season (November 2017). The results of other measurement of heavy metals of PM were far below the regulatory standards established by the domestic, world health organization (WHO) and the European Union.
The monitoring of the PM2.5 (FPM + CPM) in the discharge pipe found the concentration of four pipes were more than 20,000 μg/Nm3, which the industrial manufactory processes were Quanjin Industrial (boiler steam generation program - coal-fired boiler), Xinyi Technology (other non-metallic mineral products manufacturing procedures - sludge sintering machine), Dingbaozhen (aluminum secondary smelting process - furnace) and Taiwan sugar industry (boiler steam generation program - slag boiler). Among them, three pipes (Quanjin Industrial, Dingbaozhen and Taiwan Sugar) measured exceeded the limit of particulate pollutants (TSP) in the discharge pipeline during the test period, which is presumed to be the main cause of higher concentration of PM2.5 (FPM+CPM). Among the three coal-fired boilers (including Quanjin Industry, Guanhua Dyeing and Mengyi Enterprises), the proportion of FPM in PM2.5 was varied, ranging from 31% to 93%. Among them, Quanjin Industrial FPM accounted for the highest proportion of 93%, which was assumedly due to abnormal operation of equipment in the plant. The relatively high proportion of FPM in PM2.5 of each site found at Quanjin Industry (boiler steam generation program - coal-fired boiler), Dingbaozhen (Aluminum secondary smelting process - furnace) and Taiwan's sugar industry (boiler steam generation program - slag boiler), ranging from 64% to 93%. The proportion of CPM in PM2.5 was also varied. It was found that Mengyi Enterprise (boiler steam generation program - coal-fired boiler) accounted for 69% of the highest, followed by Senba Power (turbine power generation program - open gas turbine), Xinyi Technology (Other non-metallic mineral products manufacturing procedures - sludge sintering machine), Hongyuan industrial Co. and Yongkang incineration plants (waste incineration process - mechanical incinerator), ranging from 44% to 69%. The differences in FPM concentration were due to the different operating conditions of each sampling point, and the condition of those of the back-end pollutant control equipment. The differences in CPM concentration were due to the concentration of condensed PM2.5 as a function of the pollutant control equipment, and exhaust temperature and moisture conditions.
The results of chemical component analysis of FPM are showed as the following. The highest concentration of water-soluble ions was found at Quanjin Industry, the total concentration of water-soluble ions is 22,118 μg/Nm3, accounting for 37.7% of FPM, and the highest sodium ion content accounts for the total concentration of water-soluble ions. 76.8 %. The highest concentration of metal elements was found at Dingbaozhen, the total concentration of the metal elements is 9,448 μg/Nm3, accounting for about 32.9% of FPM, and the aluminum content is the highest at 42% of the total concentration of metal elements. The highest concentration of carbon was found at Quanjin Industry. The total concentration of carbon components is 4,223 μg/Nm3, accounting for 7.2% of FPM. The highest organic carbon (OC) content accounts for 69.2% of the total carbon concentration. The results showed the ratio of organic carbon to elemental carbon (OC/EC) greater than 2.0 was found at Quanjin Industrial, Hongyuan industrial Co., Guanhua Dyeing, Dingbaoyu and Weizhi Steel; and the ratio of organic carbon to total carbon (OC/TC) greater than 0.67, was found at Yongkang Incineration Plant, Mengyi Enterprise and Senba Power, which likely secondary aerosol aerosols can be formed.
According the results of this research, several suggestions are proposed as the following. First, it is recommended that the effective resources be applied to the environmental background investigation of the city, increase the number and frequency of PM2.5 chemical composition monitoring station, and accurately determine the source of PM2.5 chemical components in the air. And then, based on the results of the analysis, the Tainan EPB can properly allocate resources, investigate possible fixed sources of pollution in the area, and provide guidance and control for specific sources of pollution. In the short term, it should continue to urge plant-owners to replace fuel oil or coal-fired boilers with gas-fired boilers, or to recommend that the central government set the emission standards for coal-fired boilers for FPM pipelines in advance, and then control them according to the tightening standards for pollution improvement. In the medium term, the site with high emission should be required to carry out the total discharge control of the whole plant. The site is required to set the annual target of the reduction of the whole plant, and reduce its emissions year by year. The CPM emission is a common problem in the use of fossil fuel (coal, oil, gas) boilers. It is recommended that in the future, the regulation of fixed source PM2.5 emissions should not only focus on fuel oil and coal-fired boilers to change natural gas, although burning natural gas can Immediately reduce FPM, which is not helpful for CPM reduction, and the CPM regulation should be planned as soon as possible.
