Silicon Valley turns to sensors, drones and data to track landfill odours
Milpitas has spent decades living with a problem that does not fit neatly into most regulatory systems: persistent industrial odours. For residents near Newby Island landfill, the issue has been more than an annoyance. It has shaped daily routines, kept windows shut for years, and turned air quality into a civic grievance measured not in laboratory terms alone, but in missed comfort and disrupted home life.
Chia-Ling Kong, an engineer who lives about half a mile from the dump, said she could not open her window for more than 10 years after moving there. Even now, she describes two or three hours of bad smells a day. In a place known for engineering, the response is increasingly technical: local authorities have ordered landfill operators to use drones, install monitors and automate gas collection in an effort to identify the chemicals behind the smell and reduce the emissions driving it.
The logic is straightforward. Odour is often the visible symptom of a broader emissions problem, and the nuisance typically comes from a mixture of volatile compounds rather than a single culprit. Continuous monitoring can separate transient spikes from background drift, which matters when complaints arrive without warning and the wind has already carried the evidence elsewhere.
Kong said she hopes the new approach will make it easier to pinpoint a problem as soon as it begins. For communities that have spent years arguing over whether a landfill, sewage works or factory is to blame, the value of time-stamped data is hard to overstate.
Regulators are filling a gap that many countries still leave open
Odour control sits in an awkward regulatory blind spot. In the US, the Environmental Protection Agency does not regulate environmental odours as a pollutant, leaving states and local governments to decide how to handle complaints. In practice, that means the rules vary widely, while the burden of proof often lands on residents who can describe the smell but cannot measure it.
Urban growth has made the problem harder. As cities expand, homes and businesses move closer to industrial sites that were once more isolated. Land values rise, infill increases, and facilities that were tolerated at the edge of town become neighbours. Micheal Bull, an odour consultant, said people are increasingly concerned about neighbourhood stinks, especially where development has crept nearer to odorous processes.
The result is a stronger demand for technologies that can monitor, quantify and prevent smells rather than simply mask them after the fact. In a practical sense, odour complaints are not just about comfort; they are about the credibility of environmental oversight. If a community cannot distinguish between a passing plume and a chronic source, operators, regulators and residents remain locked in the same dispute.
Electronic noses are replacing drive-by sniff tests in some cities
In Des Moines, Iowa, the city has taken a more data-driven approach to a long-running odour issue known locally as the Eastside Funk. Residents have described a putrid scent drifting over parts of the city, and a study commissioned by city authorities identified a trio of industrial meat companies as among the likely sources.
Dalton Jacobus, who works in the Department of Neighborhood Services, said that within 10 miles there are about half a million people, and when the wind shifts, as many as 100,000 can end up inside the odour plume. To address that scale, the city is spending about $240,000 a year on monitoring technology.
The system uses a ring of odour monitors around suspected facilities, paired with a weather station that helps estimate where the emissions are coming from based on wind patterns. The monitors measure chemical compounds in the air in real time. In effect, they turn an intermittent complaint into a traceable environmental event.
Jacobus said the arrangement has ended much of the finger-pointing that used to follow every complaint. Instead of dispatching staff to sniff the air after the fact, officials can match a smell event to a likely source and ask what was happening at the facility at the time.
Industrial controls can remove most target compounds, but cost still shapes decisions
The technologies used to tackle industrial odours generally fall into three categories: absorb the compounds, convert them through a chemical reaction, or destroy them by combustion. When applied correctly, experts say the best systems can remove 90% or more of the target compounds responsible for smells.
The problem is cost. Some operators opt for simpler and cheaper measures, including large-scale deodoriser spraying to mask landfill or sewage odours. Bull expressed scepticism about those approaches, comparing them to fabric conditioner rather than an actual fix. The criticism is sharp but clinically relevant in a broader environmental sense: masking may change perception without reducing exposure or emissions.
Landfill remains especially difficult to treat because of its scale. Carlos Diaz, an environmental consultant based in Spain, said a landfill presents a very large surface area, which makes control more complicated than at a single enclosed industrial stack. A sprawling waste site can emit from multiple points at once, and the emissions can vary with temperature, decomposition stage and gas movement through the waste mass.
Data can settle disputes, but smell remains partly subjective
Smithfield Foods, which operates a meat processing facility in Des Moines, says it has invested $2 million in a regenerative thermal oxidiser designed to destroy chemicals associated with odours. Even so, the company says it does not believe it is the source of the complaints. The tension is familiar: one side points to emissions controls, the other to lived experience, and neither side can rely on smell alone as definitive evidence.
Before the monitors were installed, officials in Des Moines would drive out to the source of a complaint and rely on the human nose. That approach remains common in many places, but it is limited by distance, weather, timing and the inherent variability of human perception. Claudia Barrios Obregón, from Kunak, the company behind the monitors in Des Moines, said city control of odours has traditionally depended on olfactometry, in which a human panel gives an opinion on how the odour smells. She argued that this is not realistic for modern enforcement.
Electronic noses do not solve everything. They measure chemical signatures, not the full subjective experience of a smell, and they cannot guarantee that every resident will agree that the nuisance has improved. Johan Lundström, a professor in the science of smell at the Karolinska Institute in Stockholm, said perceptions of odour are deeply subjective and tend to sharpen when a smell is already judged unpleasant.
That subjectivity is one reason odour disputes can linger long after a facility has installed controls. Even so, continuous monitoring changes the debate. It gives cities a way to move beyond anecdote, and it gives residents something closer to evidence when they say the stink is real, recurring and not just imagined.