Assessing Air Quality Impacts in the Surrounding Areas of the No. 6 Naphtha Cracking Complex during Operations and Accidents

The first study used pollution roses to assess sulfur dioxide pollution in a township downwind of a large petrochemical complex based on data collected from a single air monitoring station. Our pollution roses summarized hourly sulfur dioxide concentrations at the Taishi air-quality monitoring station, located approximately 7.8-13.0 km south of the No. 6 Naphtha Cracking Complex in Taiwan, according to 36 sectors of wind direction during the pre-operational period (1995-1999) and two post-operational periods (2000-2004 and 2005-2009). The 99th percentile of hourly SO2 concentrations 350o downwind from the complex increased from 28.9 ppb in the pre-operational period to 86.2-324.2 ppb in the two post-operational periods. Downwind sulfur dioxide concentrations were particularly high during 2005-2009 at wind speeds of 6-8 m/s. Hourly sulfur dioxide levels exceeded the U.S. EPA health-based standard of 75 ppb only in the post-operational periods, with 65 exceedances from 0°-10° and 330°-350° downwind directions during 2001-2009. This study concluded that pollution roses based on a single monitoring station can be used to investigate source contributions to air pollution surrounding industrial complexes, and that it is useful to combine such directional methods with analyses of how pollution varies between different wind speeds, times of day, and periods of industrial development. The second study used pollution roses to assess volatile organic compounds (VOCs) pollution in townships neighboring a large petrochemical complex based on data collected from two air monitoring stations. Our pollution roses summarized hourly VOC concentrations from two photochemical air monitoring stations at Mailaio and Taishi Township, located approximately 3-5 km away from the No. 6 Naphtha Cracking Complex in Taiwan, according to 36 sectors of wind direction during 2009-2001 and 2007-2013. The 99th percentile of hourly concentrations of benzene and toluene downwind from the complex were 3.26 ppb - 5.27 ppb and 10.26 ppb - 8.82 ppb in two locations spanning from 300-310 degree to the east and from 330-340 degree to the sourth. Downwind benzene/toluene ratio were particularly high at wind speeds of 10-23 m/s, higher benzene/toluene ratio (> 3) were observed at 90-99 percentiles. When wind directions allow the pollutants transport from industrial area to the monitoring site, then high benzene/toluene ratio was observed. This study concluded that pollution roses based on two monitoring stations can be used to investigate source contributions to air pollution surrounding industrial complexes. Finally, the air monitors used by most regulatory authorities are designed to track the daily emissions of conventional pollutants and are not well suited for measuring hazardous air pollutants that are released from accidents such as refinery fires. By applying a wide variety of air-monitoring systems, including on-line Fourier transform infrared spectroscopy, gas chromatography with a flame ionization detector, and off-line gas chromatography-mass spectrometry for measuring hazardous air pollutants during and after a fire at a petrochemical complex in central Taiwan on May 12, 2011, we were able to detect significantly higher levels of combustion-related gaseous and particulate pollutants, refinery-related hydrocarbons, and chlorinated hydrocarbons, such as 1,2-dichloroethane, vinyl chloride monomer, and dichloromethane, inside the complex and 10 km downwind from the fire. Two back trajectories were calculated using 5-min average wind speed and direction to further confirm the high levels of hazardous air pollutants in the neighboring communities, which could be traced back to emissions from 22 plants that were shut down by the fire. This study demonstrates that hazardous air pollutants from industrial accidents can successfully be identified and traced back to their emission sources by applying a timely and comprehensive air-monitoring campaign and back trajectory air flow models.