The salts of nitrous acid are called nitrites, and pickled vegetables often contain them.
Tips
usage
亚 "sub-" marks the acid with less oxygen: 亚硝酸 (HNO2) is nitrous acid, 硝酸 (HNO3) is nitric acid. The same pair appears in 亚硫酸 "sulfurous acid" and 硫酸 "sulfuric acid".