Shell Chemicals’ new cracker plant in Beaver County has exceeded its air permit limits for two months in a row, prompting a notice of violation from the Pennsylvania Department of Environmental Protection. The petrochemical plant near Monaca was officially pronounced to be in commercial operations last month, but start up activities began months earlier. In September, the facility had by far its worst air quality month, releasing 492 tons of volatile organic compounds from its high-pressure flare, according to data submitted to the DEP by Shell. The emissions ate up 95% of the annual limit included in Shell’s air permit....