Chapter 8 — The City Has No Smell

The border between the two neighborhoods is not on the administrative map. It lies in the place where motorcyclists start to pull up their masks, where the shops close earlier, where the walls of houses change color because of the humidity. Huyen only recognized it when walking with Tung on a windy afternoon.

Heat inversion starts at 5:00 p.m. The weather report said the wind was weak, the sky was clear, and the humidity was high. There are no warnings. Station number 3 runs according to schedule, then reduces dose because the odor sensor reports low. Huyen and Tung were sent by Quynh to survey the Nam Ben route after Van sent three symptom diaries from school.

“Do you want to walk or ride?” Tung asked.

"Walking. I want to know the border at the speed of a person breathing."

He looked at her but didn't smile. Two people started from the school gate, each holding a different meter. Huyen brought sensory cards and sample bags; Tung carries flow and temperature meters and walkie-talkies. They agreed not to say any conclusions while walking, just recording the time, position, feeling and measurements.

In the school yard, there is no smell. Ground temperature 31 degrees, air layer slightly lower. Huyen feels her throat is dry. Tung recorded "no smell detected, the machine works". They passed through the western alley. An old lady watering plants said there was no sewer smell today, but her eyes were stinging. Huyen asked about the time. She pointed to the clock hanging on the porch: 5:18 p.m.

Tung looked at the meter. Synthetic gas index is still below the warning threshold.

“This is a subjective reflection,” he said.

“Recording subjective reflections.”

“Don't you want to ask what she ate?”

"I'll ask. Also write down that you watered the plants before."

The old lady heard it and said she just ate porridge and did not use chemicals. Huyen writes this as a factor that needs to be eliminated, not proof that she is right.

At station 3, Tung opened the remote control box. Spray flow was reduced by twenty percent compared to the afternoon cycle. Low odor sensor. Huyen placed a sample card in a sealed bag, opened it at each location, then closed it again after thirty seconds. She doesn't expect the card to replace the meter. She just wanted to compare how the body receives something the machine is calling low.

At the end of the alley, An stood next to his father's radio stand. He wasn't wearing a mask, but he was holding an inhaler in his hand. When he saw Huyen, he pointed to the roof opposite.

“The wind there is not like at school.”

Tung took the strip of paper from his bag and hung it on the low wire. The paper strip near the roof presses down, the strip on the outside electric pole vibrates horizontally. Same street, two heights with two directions of movement.

“The lower class is held back,” Tung said.

“For what?”

“Terrain, house, heat.”

“And the spray tower?”

“Might change the mix.”

He said “maybe” without reacting. Huyen sees it as a small change in the way he works.

An led them to a yard behind the old warehouse. He said it's easier to breathe here even though it's close to the station. Huyen checked the wind direction. The warehouse wall creates an opening, allowing the wind from the river to sneak in. Tung looked at the map and understood that the blank spot in An's map was not an error. It is where the terrain does something that the regional average cannot describe.

They continued toward the embankment. A restaurant closed even though it still had business hours. The homeowner said the guest complained of a headache, but he couldn't smell anything. Van called right away, asking if they could write down the number of people with symptoms. Tung asked the homeowner's permission, Huyen did not say the word "exposure". They recorded four guests, two employees, arrival time between 5:25 p.m. and 5:41 p.m.

“It could all be due to the heat,” Tung speak.

"Correct."

“Or from standing for a long time in a closed room.”

"Correct."

“Or something else.”

Huyen looked at him. “So we took the sample and recorded the conditions.”

At the water treatment station on the other side of the embankment, Quynh is waiting. She brought an operating map and did not ask them to say the conclusion. They stood on the concrete floor, looking at the flat river surface with no ripples. The processing system is still running. An exhaust pipe is directed through the filter before exiting.

“I want to know how close the wind is to the ground,” Quynh said. “Not a pretty chart on the screen.”

Tung pulled her to the top of the pipe and pointed to an unusual condensation. No smell. Quynh did not reach out to touch. Huyen took a condensate sample, recorded the temperature and time.

“What if we haven't seen any substance yet?” Quynh asked.

“We haven't recorded it yet,” Huyen said.

“Do you know the city doesn't like that sentence?”

"I know."

"I don't like it either. But I'm starting to understand it's necessary."

It's getting dark. Thermal inversion holds the air layer close to the ground like an upside-down glass. Station number 3 still reports low odor. Huyen took the sensory card and stood in three positions. In the first position, odorless. In second place, a very light streak of sweetness mixed in with the moist smell. In third place, there is no odor but the throat is drier.

Tung wrote it all down. “What is a sweet streak?”

“I don't call names until I have a sample.”

“Aren't you afraid of missing out?”

“I'm more afraid of giving the wrong name.”

A truck drove by, dragging a stream of air that made the strip of paper stand up. The smell of diesel comes clearly and then disappears. Huyen notes it is an easily recognizable signal. Next to it, the odorless gas layer still remains.

Tung opens average data by hour. The graph line is almost flat. Huyen asked to watch every minute. Between 5:22 p.m. and 5:36 p.m., there were three small peaks, each of which had not yet exceeded the threshold. Between the peaks are lows that keep the hourly average still green.

“What if the affected person just passes by at the peak?” Huyen asked.

“They will have symptoms but hourly reporting will not be seen.”

“What if the odor is neutralized after each peak?”

Tung looked at the injection data. Three times the system increases the short dose. “The smell can disappear before the name is called.”

No one said that was the cause. But for the first time, two people had the same question and did not need to gain the right to speak.

Quynh requested to open all minute-by-minute data for the evaluation team. Huyen asked if it could be made public.

“Not yet,” Quynh said. “I need to know if the data is wrong due to the sensor.”

“If we wait to know for sure, we will spend another night observing.”

“I can state publicly that there was a brief fluctuation, but not the source.”

Tung said: "Let's also say that the spray station has increased the dose."

Quynh turned to him. “Are you sure you want to write that down?”

“That's the engine log.”

“It can make people think the system caused it.”

“Hiding it will make people think the system is not involved.”

Quynh was silent. Huyen recorded Tung's statement but did not include it in the report as a conclusion. It stands to reason that data needs to be read together.

Near 9 p.m., the wind began to shift. The strips of paper vibrated in unison, and the smell of mud from the river returned. Huyen's throat feels better even though the city hasn't sprayed more yet. Van reported that her symptoms at school had decreased. An texted: "The map is green again, but not because it's cleaner today."

Huyen asked him why.

An sent a photo of the industrial fan in the backyard that has rotated in a new direction. “Because the wind changes.”

Save photos. A simple explanation does not impoverish the application if it is correct.

Before When leaving the station, Tung removed the cover of valve box number 3. He used a pen to mark the three minutes with peak flow, then pasted a red label on the screen: "Do not use hourly averages to evaluate heat inversion conditions."

“Who gave you permission to paste it?” Huyen asked.

"No one. I'm responsible."

“I just said Quynh's words.”

“No. I'm talking to the person who has to open this box next shift.”

Huyen looked at the dried strip of paper in her hand. The border between the two neighborhoods still does not have a name. But that night, it had an hour, a temperature, a wind direction, three small peaks flattened by the average, and there were people who had stood there long enough not to call the absence of smell a dangerous absence.

Tung brought the auxiliary machines to the maintenance room and compared the clocks of each one. One machine was four seconds slow, one was two seconds fast, and the one in the school yard lost signal just as the truck passed. No one threw any away. He created a calibration table and requested that each result be assigned a corresponding confidence level.

Huyen looked at the board and asked if the reliability made it more difficult for people to understand.

“People have had to live with errors for a long time,” Tung said. “They just didn't know what it was called before.”

An sent another page of the map. He marked locations without symptoms, not to deny the red zone but to avoid turning the entire area into a disease zone. Van is glad that he added the control layer himself.

“Where did you study?” she asked.

“Learned since everyone told me my map only had places where it was hard to breathe.”

Huyen asked if he felt misunderstood. An said that any map can be misunderstood if the reader only looks at the color they fear.

Quynh allowed the survey group to last three nights. Each night there is a mobile site low down, a site on the roof, and a person who records the wind direction with a strip of paper. Nghi joined on the second night, bringing a cloth to distinguish moisture on surfaces. Tu suggests including households that have lost their sense of smell, because they cannot confirm that the smell has returned.

The border between the two neighborhoods gradually has more people standing next to it. It still does not appear on the administrative map, but it is no longer a matter of one person's imagination. Each measurement does not produce major conclusions. It creates the possibility of returning to the right place at the right time, asking one more question, and not letting the average erase a short peak.