Recently, protests, demonstrations and riots triggered by the death of George Freud, an African American from Minnesota, appeared in many places in the United States and attracted worldwide attention. Police across the United States widely used riot control agents such as tear gas and pepper balls to drive away the protesters. In the context of the massive spread of the COVID-19 epidemic in the United States, this has raised concerns about the possibility of anti riot agents accelerating the spread of coronavirus. C&EN under the American Chemical Society made a special report on this. [1]

Tear gas, also known as tear gas, was used in the Second World War and is now widely used in riot control. It is a kind of anti riot agent. At present, the antiriot agents used in hand-held jet self-defense devices at home and abroad mainly include chloroacetophenone (CN), o-chlorophenylmethylene malonditrile (CS), capsaicin (OC), piperine, etc. Because of its low toxicity and strong efficacy, o-chlorobenzenemethylmalononitrile (CS) has gradually replaced the old tear gas chemical chloroacetophenone.

OC is an oily extract extracted from pepper plants and the main active ingredient of pepper spray. Weapon manufacturers emulsified it in water and propylene glycol, or dissolved it in organic solvents to make pepper spray. OC extract is mainly composed of capsaicin, which is a compound that makes spicy food have a hot taste. The pungency of OC pepper spray is 2000000 pungency units. In contrast, Sriracha, a popular hot sauce in the United States, has a spicy degree of 1000-2500.

When pepper spray is inhaled or absorbed by the mucous membrane of eyes or nose, the capsaicin and other substances in it will act on the pain receptor TRPV1 in nerve cells. TRPV1 is a cation channel on these neurons and plays an important role in the generation and transmission of pain. When capsaicin and other related molecules activate TRPV1, it will promote the secretion of proinflammatory neuropeptide, and the generated nerve impulse will be transmitted to the spinal cord through the central fiber, thus producing pain.

At the scene of this American riot, many cherry sized "pepper balls" produced by PepperBall Company were found. The company's website claims that this model of pellets contains 2.5 grams of irritant powder, which is composed of CS, OC or other chemical irritants. PepperBall has a series of patented technologies. When the ball is hit, it can burst quickly and release a large amount of dust and smoke to disperse people.

Marc Michael Blum, founder of Blum Scientific Services and an expert in chemical weapons, said in an interview that without any medical care, the effects of pepper spray and tear gas often disappear within 30 minutes. There is no denying that pepper spray will stimulate lung inflammation, which may be dangerous for people with respiratory problems. [1]

The effect of these chemicals is to irritate the mucous membranes of the eyes, nose and throat. They can cause people to cough, sneeze, and remove masks when trying to improve breathing. Although there is no specific study on tear gas and COVID-19. But a few years ago, Joseph Hout of the US military conducted a study on 6723 soldiers exposed to anti riot agents. It was found that there was a relationship between soldiers' diagnosis of acute respiratory diseases and exposure to anti riot agents [2]. Joseph Hout believed that the use of anti riot agents increased the damage of people's respiratory mucosa, which would increase the possibility of protesting people being infected with COVID-19. More medical experts pointed out that those who came to help people injured by anti riot agents may have close contact with people who have been infected with the virus. These people are coughing up infectious particles. In addition, those who have not been infected may face a greater risk of illness due to respiratory irritation. [3]

As for the racial conflicts behind the incident, and the various performances of the US government in the COVID-19, I don't want to comment too much. I'm right and wrong. Just to repeat, my friends who are still in the laboratory, I know that you have silently drawn the synthesis route of the above two substances, but please do not mix illegally.