Texas oil refineries released hundreds of thousands of pounds of pollutants including benzene, carbon monoxide, hydrogen sulfide, and sulfur dioxide into the air as they scrambled to shut down during last week’s deadly winter storm, Reuters reported Sunday. The extreme cold, which killed at least two dozen people in Texas and knocked out power to more than 4 million at its peak, also hit natural gas and electric generation, cutting supplies needed to run the plants. Shutdowns led to the refineries flaring, or burning and releasing gases, to prevent damage to their processing units. That flaring darkened the skies in eastern Texas with smoke visible for miles. “These emissions can dwarf the usual emissions of the refineries by orders of magnitude,” said Jane Williams, chair of the Sierra Club’s National Clean Air Team. According to data from the Texas Commission on Environmental Quality (TCEQ), the five largest refiners released almost 337,000 pounds of pollutants.

ExxonMobil’s Baytown Olefins plant in Baytown released 68,000 tons of carbon monoxide and nearly a ton of benzene in what it called a “safe utilization of the flare system.” Critics noted, however, that benzene is harmful to bone marrow, red blood cells, and the immune system. “There is no safe amount of benzene for human exposure,” Sharon Wilson, a researcher at the advocacy group Earthworks, told Reuters.

In addition to the previously mentioned pollutants, chemicals released from Texas facilities include over 6,500 pounds of the carcinogen isoprene from a Shell plant in Deer Park near Houston, as well as an indeterminate amount of methane, which is 84 times more harmful to the atmosphere than carbon dioxide over the short term.

The US National Weather Service (NWS) explained that the boiling state is suddenly freezing over because of an “Arctic outbreak” that originated just about the US-Canada border, bringing a winter snowstorm as well as plummeting temperatures. The meteorologists explained that the extreme pattern was initiated by a large and recognizable phenomenon called ‘Sudden Stratospheric Warming’, or SSW. Texans’ current chill was caused by rapid heating in the stratosphere, the second-lowest section of the atmosphere, 8-50km above the Arctic.