Stroll along the downtown streets of any major city around dinner time and it’s easy to identify the mouth-watering aromas of cooking foods. But if there’s one thing the scientists at NOAA’s Chemical Sciences Laboratory (CSL) have learned in their years investigating urban air pollution, it’s this: if you can smell it, there’s a good chance it can impact air quality. 

When it comes to those delicious food smells, the impact could be significant, according to a new study published in Atmospheric Chemistry & Physics quantifying cooking emissions in the urban air of downtown Las Vegas.

“The types of emissions we are looking at from cooking, primarily oxygenated VOCs, or volatile organic compounds, are quite reactive in the air, so we expect they’ll be important for air quality,” explained Matt Coggon, a research chemist at CSL and lead author of the study.

Coggon and his team determined that on average, 21 percent of the total mass of human-made VOCs in Las Vegas’s outdoor air were from cooking activities. Depending on the time of day, cooking VOCs ranged from 10 to 30 percent of the total.

In Coggon’s estimation, this makes cooking emissions the single largest missing source of urban VOCs in current air quality models, which could have important ramifications for regulatory policy. 

Following the smells 

NOAA and CIRES researchers in CSL have devoted the better part of a decade to identifying, quantifying, and inventorying the myriad VOCs in urban air that degrade air quality. VOCs are extremely important for urban air quality as they lead to the production of both ground-level ozone pollution and fine particulate matter (PM2.5). 

In the summer of 2021, Coggon and his colleagues in Boulder outfitted CSL’s mobile laboratory with specialized instrumentation capable of identifying and measuring hundreds of different airborne VOCs. The researchers then headed west to Las Vegas to find out how important cooking emissions might be for urban air quality. 

Home to one of the highest restaurant densities in the United States—a whopping 666 restaurants per 100,000 people—Las Vegas has been described as a “devilishly” food-obsessed city. Las Vegas also happens to have persistent air quality concerns, with significant impacts from local pollution from the Las Vegas Strip—a high-traffic entertainment district with a high density of casinos, hotels, bars, and restaurants.

For several weeks in June and July, the researchers drove their mobile laboratory around Las Vegas and the surrounding desert to map the air quality across residential, commercial, and entertainment districts. Particular focus was given to the Las Vegas Strip, cruising up and down the avenue at different times of the day and night. 

Although Las Vegas is a sprawling city, the spatial mapping revealed that cooking emissions were mostly concentrated along the Strip, roughly correlated with the density of nearby restaurants, and at highest levels during the evening hours when dining and other entertainment activities peaked.

Coggon and his colleagues also estimated the total footprint of VOC emissions in the city and where they came from. For downtown Las Vegas, they found that half of the human-caused VOC emissions were from volatile chemical products (things like perfume and scented personal care products) and the remaining half was split nearly equally between cooking emissions and vehicle traffic.

“It was surprising even to us that emissions from food cooking can be on par with vehicle traffic when it comes to VOCs,” recalled Coggon.

The team cautions that the particularly high density of restaurants in Las Vegas may mean that these measurements represent an upper limit on how much cooking matters for air quality in the U.S. Even so, research in other cities provides early indications that cooking emissions may be a big, unsolved piece of the air quality puzzle in major cities worldwide.

Although the researchers know that the kinds of VOCs emitted from cooking are reactive, just how much ozone or PM2.5 production may be attributed to these cooking emissions is still an unanswered question—one that this group of researchers is already tackling with their now more complete and accurate VOC inventory and air quality model. 

They hope that this new information will be valuable to cities such as Las Vegas that are working to address air quality concerns.