'We can't just stop breathing': A global scandal, made in Germany

Updated 1521 GMT (2321 HKT) February 22, 2018

(CNN)A piece of gray pipe hangs among the potted plants on Susanne Jallow's apartment balcony. Hidden inside the nondescript tube is a tiny computer, seven cables and a particle sensor.

In most places, the device would make for an unusual garden accessory. But it is a common sight in Stuttgart, southwest Germany, where hundreds of the gadgets hang in homes and backyards across the city.
Jallow, 55, is a lively mother of two who has lived in Stuttgart for 30 years. She uses her sensor every day to check the level of pollution -- but it's not just the numbers that tell her the air is dirty. On bad days, she can see the pollutants on the sensor itself.
"You can feel it," she told CNN last year. "When you go outside, you notice it. You get breathing problems, your throat hurts, you start being short of breath easier."
The air in Jallow's neighborhood is some of the most polluted in the country, with levels of particulate matter and nitrogen dioxide (NO2) -- both products of diesel vehicles -- often reaching dangerous levels.
Susanne Jallow got her particle sensor from Luftdaten ("air data"), a local citizens' initiative.
Last year, she and a neighbor lodged a criminal complaint against the city's mayor and district president, alleging bodily harm caused by air pollution. Jallow lost the case but hasn't stopped campaigning.
On Tuesday, Germany's highest court will decide whether diesel cars can be partially banned in German cities, including Stuttgart and Düsseldorf. Two lower courts ruled in favor of the bans last year, but the two states in which the cities are located appealed those rulings.
Jallow is eagerly awaiting the verdict, which could have far-reaching consequences for other German cities.
It's not the first time diesel is under debate in a courtroom. Since the German automaker Volkswagen was first exposed for cheating emissions tests in the United States in September 2015, hundreds of thousands of lawsuits have been launched against the company by angry owners of VW diesel cars and investors around the world.
VW admitted to illegally programming the engines in several of its diesel models to activate emission controls only during lab testing.
But outside the lab, these cars -- marketed as "clean diesel" -- were spewing out up to 40 times more nitrogen oxides (known as NOx, a group of gases that includes NO2) than the maximum allowed by US law, and up to 19 times the amount permitted in the European Union.
Several VW models marketed as "clean diesel" were later implicated in the fraud.
In the months that followed the announcement, the scale of the conspiracy -- which allegedly began in 2006 and was the subject of multiple cover-ups -- became clear.
Volkswagen said 11 million cars worldwide were fitted with software designed to cheat emissions tests. The company is facing around $30 billion in costs related to the scandal.
While two VW employees were sentenced to prison in the US in the past year, to date there have been no criminal prosecutions in Germany, the country that gave birth to the "Dieselgate" scandal.