Isoprene, a compound emitted by vegetation, could be a major contributor to secondary organic aerosols (SOA) in the atmosphere. The main evidence for this contribution were the 2‐methylbutane‐1,2,3,4‐tetraols, or 2‐methyltetrols (2‐methylerythritol and 2‐methylthreitol) present in ambient aerosols. In this work, the four stereoisomers of these tetraols were analyzed in aerosols from Aspvreten, Sweden. 2‐C‐methyl‐D‐erythritol was found in excess over its enantiomer in the Spring/Summer, by up to 29% in July. This clearly indicated some biological origins for this enantiomer, consistent with its well‐documented production by plants and other living organisms. In addition, a minimum of 20 to 60% of the mass of racemic tetraols appeared from biological origin. Thus, the SOA mass produced by isoprene in the atmosphere is less than what indicated by the 2‐methyltetrols in aerosols. Our results also demonstrate that stereochemical speciation can distinguish primary and secondary organic material in atmospheric aerosols. Key Points The first method distinguishing 1ary and 2ary organics in aerosols is proposed This method shows that the 2‐methyltetrols in some aerosols are biological The main evidence for isoprene contribution to atmospheric SOA is invalidated