Particulate organic matter from Chinese cooking
The composition of emissions from Chinese cooking could provide markers for air pollution.
Cooking fumes can contain a vast range of organic pollutants. In a study published today on ES&T’s Research ASAP website (DOI: 10.1021/es0614518), a team from Peking University (China) characterized the organic content of fine particulate matter from four restaurants, each serving a different style of cuisine. The extensive analyses allowed the authors to identify potential organic markers that are specific to Chinese cooking and to calculate the percentage of particulate organic matter (POM) that ends up in the atmosphere.
“Aerosols generated from cooking can be a major source of indoor air pollution and can also be an important contributor to ambient air pollution,” says Christopher Simpson, a University of Washington researcher who looks at biomarkers of particulate matter exposure. “Incomplete combustion of organic materials produces a complex mixture of chemicals; many are known to be irritant[s], toxic or carcinogenic to humans.”
Reports from the U.S. estimate that cooking meat contributes as much as 20% of the POM that goes into the atmosphere. Whereas POM released from cooking has been examined for decades, mainly in the U.S., studies from China have been relatively scarce.
The chemical composition of emitted particles strongly depends on the cooking method, fuel source, ingredients, oil, and temperature. Chinese cooking usually employs natural gas at high temperatures, and the ingredients are all cooked together. “The fume[s] from the heating oil, along with mixing a complex mixture of ingredients, including meats and vegetables, [contain] certain compounds fairly specific to the cooking process,” says Jim Zhang, a professor at the University of Medicine and Dentistry of New Jersey and Rutgers University.
Chinese food can be divided roughly into eight representative regional cuisines from Anhui, Fujian, Guangdong (Canton), Hunan, Jiangsu, Shandong, Szechuan, and Zhejiang. Other famous local culinary styles include Shanghai, Yunnan, Uygur, and Dongbei. Each cuisine has its own distinct style, taste, and ingredients.
Focusing on the exhausts from four different restaurants in the city of Guangzhou, researchers from the State Key Joint Laboratory of Environmental Simulation and Pollution Control, at Peking University, examined Szechuan, Dongbei, Cantonese, and Hunan food. They found that “in general, no large differences exist in emissions of the organic compounds between the tested restaurants,” says the study’s coauthor Yunling Zhao, who is now at Rutgers University. Zhao points out that although the concentrations varied significantly among the restaurants, the ratios of the quantified compounds and the homologue profiles are similar.
The team compared their results with previous reports from two restaurants in Shenzhen and with studies on cooking meat. Hunan and Cantonese restaurants in Guangzhou and Shenzhen had some differences, mainly from the use of different cooking ingredients—for example, different brands of cooking oil.
The researchers also found that some of the compounds emitted, such as β-sitosterol and levoglucosan, cannot be found in POM from cooking meat. The presence of these compounds makes them good candidates for organic tracers for Chinese cooking. For example, the ratio of hexadecanoic acid to levoglucosan is 80 times higher than that found in ambient air. The authors estimate the percentage of hexadecanoic acid released into the atmosphere from Chinese cooking to be around 1.3%. Meat-cooking procedures have been estimated to account for about 40% of the hexadecanoic acid emissions in the Los Angeles area.
Zhang, who is at Rutgers but did not participate in the research, comments that because some of the identified compounds are carcinogens (e.g., benzo[a]pyrene), characterizing the cooking fumes is important. “Epidemiological studies have identified associations between high-temperature frying and lung cancer,” he says.
“Most previous studies on Chinese cooking mainly focused on [a limited number of] special compounds, like PAHs, which cannot provide a complete picture of what [kind of] components Chinese cooking releases,” says coauthor Zhao. Min Hu, the study’s lead author, says she hopes that the results from this research “will help to estimate the contribution of Chinese cooking to atmospheric POM.”
