Thursday, Aug 17, 2017, 9:58 AM CST – China


Odor Testers

Nasal Officers

Perfumiers require a sharp nose, but to become an “odor tester,” whose profession is to sift safe from potentially dangerous smells, it seems any nose will do

Chen Yuanyuan injects an odor sample to a bag filled with clean air Photo by dong Jiexu

Odor samples collected from factories, landfills and sewage treatment plants Photo by dong Jiexu

The human eye is able to distinguish millions of colors in the various wavelengths and intensities of light. The human ear can recognize 500,000 distinct frequencies. How many smells the human nose can identify, however, remains a mystery.

A research paper published in Science in March 2014 reported that the human nose is capable of sensing at least a trillion individual aromas, far more than was previously thought. However, few people have to push their proboscis that far. Even a professional perfumier – a job that requires inborn ability and years of formal training – only needs to recognize and recall around 400 fragrances. For an “odor tester,” however, China’s latest weapon in the fight against pollution, a sensory memory of five smells will suffice.


The Beijing Municipal Environmental Monitoring Center (BMEMC) is a pioneering institution in China that has conducted odor testing since its inception in the 1970s. Senior engineer Chen Yuanyuan is one of its staff of 40 odor testers who has worked in this little-known area for more than 10 years.

The main task of an odor tester, as a relatively new occupation, is to gauge pollution levels from odor samples collected at places including factories, landfills and sewage treatment plants. As is the case for her colleagues, odor testing is not a full-time job for Chen. She is a quality and technical supervisor by day; she only moonlights as an odor tester when called into the BMEMC laboratory.

Since 1994, when China unveiled its Standards for the Discharge of Odor Pollutants, odor testers became a crucial, if part-time, tool in the country’s environmental protection industry. In 2004, China began to issue work licenses for odor testers if they passed a qualification test.

“It is a part-time job, and to ensure [we have] sufficient personnel, every newly recruited colleague, in whatever department, is advised to sit the [odor tester] exam,” Chen told NewsChina.

Chen added that an odor tester needs no more than an “ordinary nose,” not the finely honed sense of smell of a perfumier or food tester. In fact, she told our reporter, a keen sense of smell could prove a detriment, as it would be likely to “affect judgment, because it is not a true reflection of the average person.”

According to Chen Wei (no relation to Chen Yuanyuan), another engineer at the BMEMC analysis laboratory, recruitment requirements for an odor tester are not complicated. Anybody who passes the exam can take the job so long as they are aged between 10 and 45, do not smoke or drink and do not have any olfactory disorders. Reassessment is compulsory every three years.

“Candidates have to recognize five smells, including the fragrance of a flower, the stink of sweat and an unpleasant stench infused into diluted test paper. One mistake means they fail,” said Chen Wei.


Essentially, the job of an odor tester is to gauge whether an odor is unpleasant or not. Despite the simplicity of this task, the verdicts of odor testers directly influence the application of polluting emissions regulations by China’s environmental and law enforcement agencies.

When an investigation occurs, samples of suspect odors are taken at two-hour intervals at four monitoring stations attached to emissions vents around the site in question. These are then passed directly to the BMEMC lab for testing.

Chen Wei told our reporter that, generally speaking, odor testers can only work two sites per day. “Their sense of smell will be affected if they are exposed to a single odor for a long time,” she said.

In the lab, six odor testers, one assistant and a senior tester will test a total of 18 “olfactory bags” – containers of clean, odorless air, some of which have had particles of one sample introduced into them. The six odor testers will work in isolation to determine which olfactory bags contain the samples. To ensure accuracy, each group’s olfactory bags have to be tested three times. The assistant will gradually increase the dilution of the sample until it can no longer be detected by most of the testers, at which time the overseer will determine whether or not the sample exceeds acceptable levels.

According to Chen Yuanyuan, this methodology is an adaptation of Japanese techniques, adopted in place of the dynamic dilution olfactometers, or “artificial noses” widely used in the US and Europe. She told our reporter that there is no major difference between the two methods in terms of reliability and validity.


The BMEMC is mainly responsible for the environmental monitoring as well as the emergency monitoring of air, water and noise pollution. Odors, for the purposes of the BMEMC, are unpleasant smells that are not always indicative of a threat to public health. Testing these smells is just one minor aspect of the agency’s workload.

The BMEMC conducts two routine odor tests each year targeting the city’s landfills and pollutant-discharge facilities. Chen Wei said that many people have mocked the gauging of odors through human noses, calling the technique primitive and unreliable, but he maintains that, currently, “human noses work much better than instruments.”

According to the national Standards for the Discharge of Odor Pollutants, there are nine control indexes for the discharge of odorous pollutants in China, only two of which – ammonia and hydrogen sulfide – can be effectively detected entirely by monitoring equipment. Chen Yuanyuan told NewsChina that the human nose, meanwhile, can sense over 4,000 distinct odors.

“Some enterprises have installed monitoring devices [to detect odors] by themselves, but, generally speaking, the instruments remain in the early stages of development and haven’t been widely adopted in other countries,” Chen continued. “The ratio between input and output leaves much to be desired. Such instruments are also likely to be affected by environmental changes. Sensors are susceptible to dysfunction as a result of changes in humidity or temperature.”

On top of scheduled and random testing, the BMEMC also investigates public complaints of suspect smells – a common phenomenon in Beijing. Chen Yuanyuan still recalls initiating emergency monitoring of a pharmaceutical factory in 2008 after a tip-off from a member of the public, later discovering that the factory was indeed secretly flouting emissions regulations. She told NewsChina that the factory would vent pollutants at night to evade the attention of the environmental protection authorities.

In recent years, Chen continued, district- and county-level environmental monitoring stations are now assisting with investigating bad smells, significantly easing the burden on the BMEMC. More and better laboratories have sped up response times, even as public attention has shifted away from bad smells and towards Beijing’s ubiquitous smog, and the levels of PM 2.5 (particulate matter less than 2.5 micrometers in diameter, capable of penetrating the lining of the lungs), which today are a much bigger concern than malodorous landfills.

“PM 2.5 [levels] are visible, but odors can only be smelled,” said Chen.


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