20th-century Dutch chemists

Jan Theodoor Gerard Overbeek (Groningen, January 30, 1911 – February 19, 2007) was a Dutch professor of physical chemistry at the Utrecht University.

Ernst Julius Cohen ForMemRS (7 March 1869 – 6 March 1944) was a Dutch Jewish chemist known for his work on the allotropy of metals. Cohen studied chemistry under Svante Arrhenius in Stockholm, Henri Moissan at Paris, and Jacobus van't Hoff at Amsterdam. In 1893 he became Van't Hoff's assistant and in 1902 he became professor of Physical Chemistry at the University of Utrecht, a position which he held until his retirement in 1939. Throughout his life, Cohen studied the allotropy of tin.
Cohen's areas of research included polymorphism of both elements and compounds, photographic chemistry, electrochemistry, pizeochemistry, and the history of science. He published more than 400 papers and numerous books.In 1913 he became member of the Royal Netherlands Academy of Arts and Sciences. He was elected a Foreign Member of the Royal Society in 1926. Following the 29 April 1942 decree that Dutch Jews wear the yellow badge, he was arrested by Nazi police for non-compliance and forced to resign.According to Margit Szöllösi-Janze, in her book, Science in the Third Reich, Cohen "put great efforts into restoring the relationships of Western European scientists with their German colleagues after the First World War."
He was killed on 6 March 1944 in a gas chamber at Auschwitz concentration camp.

Arie Jan Haagen-Smit (December 22, 1900 – March 17, 1977) was a Dutch chemist. He is best known for linking the smog in Southern California to automobiles and is therefore known by many as the "father" of air pollution control. After serving as an original board member of the Motor Vehicle Pollution Control Board, formed in 1960 to combat the smog, Dr. Haagen-Smit became the California Air Resources Board's first chairman in 1968. Shortly before his death in Pasadena, California, of lung cancer, the Air Resources Board's El Monte Laboratory was named after him.