Chapter 4 — The City Has No Smell

Vu An does not call his map a disease map. He calls it a map of the places the body wants to return to. The blue roads lead from the school to his father's radio booth, the yellow ones follow the embankment, and the red only appears in the places where he has to stop to breathe. You don't paint the whole city. He only drew places where he had traveled enough to notice a slight change.

Huyen spread the map out on the table in Van's clinic. The paper has been folded open many times, the folds have turned brown. In the right corner, An wrote the date in very even numbers. You don't write "difficulty breathing" in every red dot. There are points that say "dry", points that say "severe", points that say "need to sit", points that say "unclear due to previous cough".

“Who taught you to write like that?” Huyen asked.

"No one. If we put it all together, my father would say the map is useless."

Van burst out laughing. "Your father is half right. The map is not enough to diagnose, but it is enough to find places to ask more questions."

Huyen uses a pencil to draw a line from the red points to the Clean Class station location. There are a few overlapping points, a few far away points, one point is located in an area without any stations. She did not highlight that line. A seam can easily make people think the cause has appeared.

“What if we remove the spray station from the map?” An asked.

“I will know that your body still has its own geography.”

“You talk like an adult.”

“You are an adult.”

“Adults often draw lines between things that are not necessarily related.”

Huyen looked at him. “So how do you want to draw?”

An took a gray pen and drew arrows that did not form lines. Arrows indicate wind direction, vehicle direction, and pedestrian direction. You said the symptoms are not a static point. It can follow people from the school gate to the bus stop, or appear after the spray truck has left the street.

Van opened the examination records of six other students. She asked for permission from the parents not to put her name on the map. During ten days, four children had increased symptoms when the spray station was operating, two did not. Children without symptoms all study in the east-facing building, which has its own exhaust fan. Huyen notes, does not turn the difference into a conclusion.

“I want to create a three-week diary,” Van said. "Each student records time, place, symptoms, medications, previous activities. The school records fan schedule and spray schedule. If possible, add temperature and wind direction."

The principal walked in just in time. He frowned when he heard the word "spray schedule".

“We should not make students afraid of the city-vetted system.”

Van put down the file. “Monitoring symptoms does not teach children to be afraid.”

"But the red map will be shared. Parents can demand school closure."

Huyen asked: "If the red map is not shared, do you want to see the full version?"

The principal was silent. This is a difficult question because it leaves no room for easy objection. He wants the school to be safe, but he also wants no one to say the school is having problems during the clean city announcement ceremony.

“I need to make sure the data is secure,” he said.

“Okay. But the data can't just be given to people whose interests are in keeping a good image.”

Van looked at Huyen, as if reminding her not to turn the meeting into a debate session. Huyen lowered his voice and proposed three layers of data: a separate version for doctors, an anonymous version for the evaluation team, and a comprehensive version for parents. The principal agreed to try for two weeks.

Tung went to school at noon to check station number 3. Huyen followed him to the roof. Looking down from there, silver spray trucks run between the rows of houses. Tung placed the flow meter in the cabinet and checked a small valve.

“Has this station changed since yesterday?” Huyen asked.

“The pressure is fine.”

“Not the question I asked.”

He removed the sensor box cover. “There was an automatic compensation cycle at 0943. I noted it in the log.”

“What is the compensation cycle based on?”

“Smell sensor reported lower than expected.”

“What if it says low because the smell has been neutralized?”

Tung put down the screwdriver. “You're saying the system makes you think it doesn't need to work.”

“I'm talking about the loop.”

He looked at the screen. “I need proof.”

“That's why I started a diary.”

Tung gave her a chart. After each spray, the odor sensor drops to low for about fifteen minutes. If a new odorant arrives, the system increases the dose. But if the new substance is not in the sensor group, the station will still report low. The system doesn't know it's missing something that's not in the training set.

“What does this mean?” Huyen asked.

“Which means we need to know which groups it doesn't measure.”

“And the school is right below it.”

Tung shook his head. “It doesn't mean the station makes it difficult for students to breathe.”

“I haven't said that.”

“But anyone who reads the report will hear the same thing.”

Huyen put the map in his briefcase. “Then help me write a report that is accurate enough so people don't have to listen with fear.”

Tung did not answer. He used his hand to gently tap on the pipe, hearing a metallic response. A hollow vibration at the connection near the auxiliary pump.

“This part may have air bubbles,” he said. “It causes traffic to fluctuate for short periods of time.”

“Does it affect the spray dose?”

"Maybe. I need to remove the pipe after class."

In the medical room, An is adding maps. He drew a light blue line across the gymnasium, where the wind came from the riverbank. Huyen asked why it wasn't marked in red.

"There I was running. I was having trouble breathing because of the running. I don't know if it had anything else to do with it."

“Good,” Huyen said.

An looked up. “What good?”

“You're holding back another possibility.”

“You want my map to have a lot of things, aren't you sure?”

"A good map is not one that only has certainties. It tells us where to check."

An thought about it and then drew a square next to the green area. In the box, he wrote: "running fast, strong wind, unknown."

In the afternoon, Van sent Huyen the diary list. She added a “does it smell” column? Five students recorded no notice. One child noted the smell of hot plastic on a day the station was running late. Huyen suggested not removing that column even though the answer is usually no.

On the way out of school, Huyen met a parent waiting for her child. The woman asked her if the center had discovered that the city was causing the disease. Huyen said there is no conclusion yet. The woman asked if she should take her child out of school. Huyen said she cannot decide for her family, but can help the school monitor specific conditions.

“If you don't know, how will we know?”

Huyen looked towards the spray station. “By not turning the unknown into the unasked.”

That night, she imported An's map into the file, placing the symptoms layer next to the operations layer, the terrain layer, and the weather layer. Overlapping areas appear, but none of the colors automatically change to red. She sent requests to Tung for traffic data, to Quynh for operating schedules, and to Van for symptom logs.

Quynh answered faster than she thought: "I agree to provide data within the scope of confidentiality. But please do not use the student map." to conclude the source of emissions.”

Huyen texted back: "I also don't want to use it to conclude. I want the city to be serious enough not to ignore it.”

Before going to bed, Huyen opened her personal notebook. She drew a small box on the edge of the page, writing “zero odor.” Next to it are three arrows: sensory council, station number 3, An's breathing map. They do not yet constitute an answer.

But for the first time, nasal silence had an address.

Van set up a paper mailbox in the health room so students can leave their diaries without having to speak in front of the class. The box did not ask the children if they smelled anything. It just has boxes for hours, locations, activities, symptoms, and things that make it easier. Huyen suggested adding the box "don't know", because many students cannot distinguish between shortness of breath caused by running, heat or air.

On the first day there were twenty-one votes. Fourteen votes recorded no odor. Six coupons recorded car smell, hot plastic smell or food smell. One ticket only had a picture of a closed door. Van did not return any ballots because of missing words. She called the student up and asked what that picture meant. She replied: "I want to leave that place but I don't know where to go."

Huyen wrote down the entire sentence, then asked the principal if he could use the temporary shelter list. The school doesn't exist yet. They created a simple plan: library facing east, medical room, classroom with filter fans and staff. Each room has a maximum number of people, update time and person responsible for opening the door. That's not an evacuation order. It is a way for the body to have a place to stop before anyone knows the cause.

Tung sent station 3's traffic data, but there was a delay of seven minutes. He wrote that the reason was that the server changed source. Huyen asked if the time he died coincided with the time An had difficulty breathing. Partial overlap. She did not fill the gap with speculation. She marked it on the map with a dashed line.

An looked at the broken line and said: "I like this place better than the solid line."

“Because it's more real?”

“Because I can still keep going.”

Huyen put the statement in the notebook and did not include it in the report. She began to understand that maps were more than just a way to see where danger was. It also tells one where to return with better equipment, a different question, or someone who knows the terrain better.