Chemical Synthesis of Multifunctional Air Pollutants: Terpene-Derived Nitrooxy Organosulfates

Nitrooxy organosulfates derived from terpenes (NOSTP) represent an important class of products formed between anthropogenic pollution (e.g., SO2 and NOx) and natural emissions. NOSTP compounds have been consistently detected in atmospheric environments under varying urban influences. Their chemical linkages to both anthroposphere and biosphere make them valuable markers for tracking anthroposphere-biosphere interactions. However, their quantification, formation, and transformation kinetics in atmospheric aerosols are hindered due to the lack of NOSTP standards. In this work, we developed two routes for the first concise chemical synthesis of eight NOSTP from terpenes including alpha-pinene, beta-pinene, limonene, limonaketone, and beta-caryophyllene. Subsequently, six of the synthesized NOSTP were for the first time positively identified in ambient aerosol samples, clarifying certain misidentifications in previous studies. More significantly, the availability of authentic standards allows irrefutable observation of three carbon skeleton-rearranged NOSTP, two derived from alpha-pinene, and one derived from beta-caryophyllene, revealing the occurrence of previously unrecognized transformation pathways in the formation of NOSTP. Two synthesized NOSTP from beta-pinene and limonene could not be detected, likely due to rapid hydrolysis of their immediate hydroxynitrate precursors outcompeting sulfation. Such mechanistic evidence is valuable in understanding the atmospheric chemistry of NOSTP and related compounds. This work demonstrates the usefulness of authentic standards in probing the NOSTP formation mechanisms in the atmosphere. Comparison of NOSTP ambient samples collected from four Chinese cities in two winter months indicates that anthropogenic chemical factors could outcompete terpene emissions in the formation of NOSTP.

Automated summary

Nitrooxy organosulfates derived from terpenes (NOSTP) are important products formed between anthropogenic pollution and natural emissions, but quantification, formation, and transformation in atmospheric aerosols are hindered by the lack of standards. This work developed synthesis routes for eight NOSTP compounds and identified six synthesized NOSTP in ambient aerosol samples for the first time. Availability of authentic standards allowed observation of previously unrecognized transformation pathways in NOSTP formation.