| Coke production in China accounts for 60% of the world’s total production. Coking production process is one of the important sources of organic pollutants and seriously impacts on the surrounding environment of coke oven. Organic pollutants associated with fine particles are easy to enter the body through breathing and are seriously hazardous to health. The study on air pollutant characteristics in surrounding of mechanical coke oven is of great significance for the research on migration transformation law, and provides the important basis for the establishment of organic pollutant diffusion model. The ambient air of six representative mechanical coke ovens was selected in this study, particulate and gaseous samples were collected in surrounding of coke oven. Polycyclic aromatic hydrocarbons (PAHs) were analyzed by gas chromatography-mass spectrometry (GC-MS), and Organic carbon (OC) and elemental carbon (EC) were analyzed by Elemetar Analysensysteme GmbH vario EL cube. The concentration levels, size distributions, and spatial distributions of PAHs, OC, and EC were analyzed, the adhesion mechanism of PAHs associated with particles was investigated, and the carcinogenic potency of PAHs to human health was discussed. The main conclusions are as follows.1. The 16 PAHs total concentrations were in the range of 3376.69～18160.95ng/m3 in the ambient air of coking plants. Benzo(a)pyrene (BaP) is a characteristic pollutant emitted from coking production process, and the average concentration of BaP was 51.22ng/m3. The total BaP equivalent concentration (BaPeq) was 262.06ng/m3, which was five times of BaP concentration. The exposure risk of PAHs to coking plant workers decreased with the increase of coke oven height. There was a perfect correlation between the gas/particle partition coefficients and sub-cooled liquid vapor pressure of PAHs with 0.90 for r2 and -0.446 for mr. Absorption was the main mechanism of gas/particle partitioning for PAHs in the coking plant atmosphere. Naphthalene, phenanthrene, dibenzo[a,h]anthracene, benzo[a]pyrene and benzo[b]]fluoranthene should be taken as the preferred monitoring pollutants in the surrounding of mechanical coke oven.2. The concentration and toxicity levels of 10 PAHs associated with particle less than 2.1μm were significantly higher than those in other size particles. The size distributions of total PAHs and individual PAHs (except fluoranthene) exhibited a considerable peak in particles less than 2.1μm, and the size distributions of individual PAHs show an increase in the fraction of PAHs as ring number and molecular weight increase.3. The distribution characteristic of individual PAHs in the downwind of coke oven was similar to that in machine side, but significantly different from that in coke side. The particle-phase PAHs in surrounding of mechanical coke oven were mainly associated with PM10.The profiles of individual PAHs in PM10 round the coke oven are consistent:the relative contributions of chrysene, benzo(a)anthracene, benzo(b)fluoranthene, benzo(k)fluoranthene and BaP to ∑12PAHs range from 61.68% to 77.58%, among which the ones of chrysene are the highest (21.54%～26.59%), and the ones of benzo(a)pyrene range from 7.56% to 11.36%. Dibenzo(a,h)anthracene is the highest contributor to the total BaPeq of ∑12PAHs, followed by benzo(a)pyrene. There was no obvious change in different downwind sites of coke oven, and BaP concentration was two times of that in control site. BaP concentration in the plant boundary was 4.9 times of standard value provided by Emission Standard of Pollutants for Coking Chemical industry (GB 16171-2012). The percentage of gas-phase PAHs on the coke side was slightly lower than that of particle-phase. The percentages of gas-phase PAHs in other sampling sites were higher than those of particle-phase, and the percentage of gas-phase PAHs increased with the distance from the coke oven increased. The mechanism of gas/particle partitioning for PAHs was absorption mechanism in surrounding of mechanical coke oven.3. The mass concentrations of organic carbon (OC) and elemental (EC) associated with TSP in the coke oven top were 291.60μg/m3 and 255.05μg/m3, while those in the plant area were 377.76μg/m3 and 151.73μg/m3. The EC concentration in plant area was lower than that in the coke oven top, while OC concentration was significantly higher than that in the coke oven top. The OC and EC in particles, which were collected both in the coke oven top and plant area, were mainly enriched in fine particles. The size distribution of OC exhibited a peak within the 1.4～2. 1μm size range in the coke oven top, while a unimodal distribution in the particles less than 1.4μm in the plant area. OC in the plant area was more preferably enriched in fine particles than that in the coke oven top, and the same size distribution of EC were present in the coke oven top and plant area. The direct source of OC and EC associated with TSP was coking process in surrounding of mechanical coke oven, and the contribution of secondary sources was higher downwind of the coke oven than those in other sampling sites. In order to reduce the exposure risk of OC on coking plant workers, the primary organic carbon (POC) directly emitted from coking process should be monitored, and the SOC pollution also should be reduced though releasing the SOC precursor emission.5. The value of OC/EC in particles less than 2.1μm was 1.3 in the coke oven top, which has important significance for source apportionment. In the plant area, the concentration of secondary organic carbon (SOC) in particles with size of≤1.4μm was the highest among all size ranges, and the contribution of SOC to OC was higher in 1.4～2.1μm and≤1.4μm ranges. In the plant area, the mass concentration of SOC and the contribution of SOC to OC increased with the diameter decreasing in the particles less than 10.2μm.6. Total PAHs had better positive correlation with OC, while there was no clear correlation between total PAHs and EC in the ambient air of plant area. Individual PAHs had better correlations with OC than with EC, and PAHs with 4～6 rings had better correlations with OC than PAHs with 2～3 rings. In the sites near the mechanical coke oven, PAHs were significantly correlated to OC and EC in particles, and the correlation coefficient increased with the increase of molecular weight and rings. BaP had good correlation with EC and with OC, and the correlation coefficients were 0.918and 0.884, respectively. The linear regression equation of y=2.245x-0.068 can characterize the relationship of BaP and EC, and y=1.756x+105.027 for BaP and OC. |
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