Environmental groups and other critics of Volkswagen said the suspension of Mr. Steg, whose formal title at Volkswagen is head of external relations and sustainability, made him a sacrificial lamb meant to insulate the company’s top managers from consequences.
These critics drew parallels with the Volkswagen emissions scandal, in which the company initially said that a small number of rogue engineers were responsible for installing software intended to dupe regulators. German prosecutors have since identified dozens of suspects.
“They are again playing the game where the subordinates were the culprits,” said Christian Strenger, a former member of a commission that wrote Germany’s rules on corporate governance. Mr. Strenger is among the people suing Volkswagen for violating its legal obligations to shareholders.
Karmenu Vella, the European commissioner responsible for environmental matters, met with ministers from the nine offending countries in Brussels on Tuesday and said afterward that they had failed to present credible plans for reducing pollution.
Mr. Vella said 400,000 people in the European Union died prematurely each year as a result of air pollution from all sources “because of a massive, widespread failure to address the problem.” He expressed frustration that “a sense of urgency is not always evident across member states.”
The experiments that preceded Mr. Steg’s suspension were conducted at a laboratory in Albuquerque for the European Research Group on Environment and Health in the Transport Sector, known by its German initials, E.U.G.T.
Although ostensibly independent, the organization was financed entirely by Volkswagen, Daimler and BMW. (Bosch, a major German auto parts supplier, had been a member but dropped out in 2013.) In recent days, the three carmakers have repudiated the work of the group, which folded last year.
Yet all three were represented on the organization’s five-person board of directors, and all three contributed money to the group. The research on monkeys had a budget of more than $700,000, and was just one of the organization’s numerous projects.
Another study financed by the group subjected 25 volunteers to low doses of nitrogen dioxide. The research, conducted in 2015, was authorized by an ethics commission at the RWTH Aachen University in Aachen, Germany, where it took place.
Nonetheless, images of humans being exposed to gas in airtight chambers raised uncomfortable associations with Germany’s Nazi past.
The experiments on monkeys at the Lovelace Respiratory Research Institute in Albuquerque — carried out in 2014, a year before Volkswagen was caught using software to cloak excess diesel emissions — involved exposing a group of the animals to exhaust from a late-model diesel Volkswagen; a second group of monkeys was exposed to exhaust from an older Ford diesel pickup truck.
After breathing diluted exhaust for four hours, the monkeys were examined for signs of lung inflammation or other ill effects. The research did not kill the monkeys, but it was unclear what happened to them after the experiments were completed.
Results of the research had not been published by the time the E.U.G.T. disbanded last year.
Matthias Müller, Volkswagen’s chief executive, said in a statement Tuesday that the company is conducting a thorough investigation of the research “and will draw all the necessary consequences.”