US cities deploy sensor networks to trace industrial odors to their sources

EPA does not regulate environmental odors, leaving oversight to states and cities

The cities of Milpitas, California, and Des Moines, Iowa, are turning to drone-deployed sensors and electronic-nose monitoring networks to track the chemical compounds behind industrial odors and pinpoint the facilities responsible. The deployments come as residents in both cities have long complained about smells drifting from landfills and meat-processing plants, and as urban expansion has pushed neighborhoods closer to industrial operations that historically sat apart from homes.

In Milpitas, the operators of the 342-acre Newby Island landfill have been ordered by local authorities to deploy drones, install monitors to systematically track the chemicals responsible for bad odors, and automate the collection of landfill gases blamed for smells. Chia-Ling Kong, an engineer for a tech firm who lives around half a mile from the dump, said the smell had kept her from opening her windows for more than 10 years after she moved in. “When I first moved here, I could not open my window for over 10 years,” Kong said, adding that she and her neighbors still endure roughly two to three hours of bad smells each day. “Hopefully with this continuous monitoring, it makes it easier to pinpoint problems at the moment it starts,” she said. The landfill’s operators said they were committed to operating it safely and protecting air quality.

In Des Moines, the persistent smell locals call the “Eastside Funk” prompted city authorities to identify, through a commissioned study, a trio of industrial meat companies among the culprits. Officials now spend about $240,000 (£182,000) a year on a ring of electronic-nose monitors placed around suspected facilities. Dalton Jacobus, who works in the Department of Neighborhood Services, said the monitors, paired with a weather station, give officials real-time data on which facility is releasing which compounds based on wind patterns. “Within 10 miles, there’s about half a million people,” Jacobus said, adding that, depending on wind direction, “100,000 people can be in the middle of that odour plume.” According to Jacobus, the system has put an end to finger-pointing about which facility is to blame each time a smell sparks complaints. “Now we can say with reasonable certainty that ‘this odour event did originate from your facility, what was going on,’” he said. Before installing the monitors, which some local companies help pay for, officials in Des Moines would drive out to the source of a complaint to sniff the air.

At least one of the companies identified in the Des Moines study has invested in its own controls. Smithfield Foods, which operates a meat processing facility in the city, said it has installed a regenerative thermal oxidiser, which destroys the chemicals associated with bad smells, at a cost of $2 million. Even so, the company said it does not believe it is the source of odour complaints. The Des Moines network’s monitors are made by Kunak, a Spanish company whose representatives argue the technology is more reliable than human smell panels.

Industrial odor-control technologies broadly fall into three categories: absorption, chemical conversion, and thermal destruction. Odour-control experts say the best systems, when used correctly, can remove 90% or more of the target compounds responsible for smells. Some operators instead opt to spray large volumes of deodorizers that mask rather than eliminate odors. Micheal Bull, an odour consultant, likened such masking products to fabric conditioner. “In my view they’re not likely to change the odours,” Bull said of industrial-scale air fresheners. Carlos Diaz, an environmental consultant based in Spain, said landfill odors are among the most difficult to resolve because waste sites present a very large surface area to the air.

The technology rollout highlights a gap in US environmental regulation. The federal Environmental Protection Agency does not classify environmental odors as a pollutant, leaving oversight to states and local governments. Bull, speaking about his work in the UK but in terms that apply to many countries, said urban infill and rising land values have pushed housing developments closer to existing industrial sites, intensifying the conflict. “You’re getting developments being built nearer to odorous processes… as land has become more valuable, there is also infilling,” he said.

Claudia Barrios Obregón, of Kunak, said many cities still rely on so-called olfactometry — human panels that smell and evaluate odors — to gauge industrial smells. “Right now, the way that cities control or measure odours is olfactometry: a human panel measures and gives an opinion of what the odour is like. But that’s not that realistic,” she said. Johan Lundström, a professor who studies the science of smell at the Karolinska Institute in Stockholm, noted that perception of odor varies widely from person to person. “Unfortunately, the general rule is that the nastier we perceive the odour to be, the more sensitive towards it we are,” Lundström said.

Many countries have no regulations in place for managing industrial smells, leaving communities to organize on their own. In Milpitas, Kong is part of a citizens’ campaign that has pushed for the new monitoring order. Whatever technology is used, it can be hard to keep everyone happy, as smells are so subjective.