# Computational Exploration of the Ability of the 2‑Methyltetrols Produced from Photooxidation of Isoprene to Form Prenucleation Complexes

## TL;DR

This study investigates whether 2-methyltetrols, formed from isoprene, can form prenucleation clusters with sulfuric acid and water, finding they are unlikely to contribute to aerosol formation.

## Contribution

The study provides high-level computational analysis of 2-methyltetrols' ability to form prenucleation complexes, offering new insights into their role in atmospheric aerosol formation.

## Key findings

- 2-methyltetrols bind to one to three water molecules at high concentrations.
- Sulfuric acid–tetrol–water complexes form at lower concentrations.
- Tetrols are unlikely to form prenucleation clusters that lead to aerosol growth.

## Abstract

A central question
in the formation of secondary aerosols
is whether
organic molecules participate in the formation of prenucleation clusters
or are they only adsorbed after formation of larger aerosols? The
difficulty in understanding the role of organic molecules in aerosol
formation is that there are very few studies of prenucleation clusters
produced from various organics and sulfuric acid, so it is uncertain
whether organic compounds form prenucleation clusters. Isoprene is
the most abundant volatile biogenic organic compound (VOC) emitted
into the atmosphere, accounting for about 70% of biogenic VOC emissions,
excluding methane. Each year, approximately 600 teragrams of isoprene
enter the atmosphere, primarily from natural sources like vegetation.
This makes it a significant component of atmospheric organic molecules,
much more prevalent than other VOCs emitted by plants or anthropogenic
activities. Photooxidation of isoprene produces the diastereomeric
tetrols, 2-methylthreitol and 2-methylerythritol, which contain four
hydroxyl groups. We completed a comprehensive conformational search
of both tetrols, and extensively explored the potential energy surfaces
of these tetrols complexed with sulfuric acid and water. We report
the vast ensemble of structures that are within 1 kcal/mol of the
DLPNO-CCSD­(T)/CBS//ωB97X-D/6-31++G** minimum for each system.
These high level ΔG° values for each system
were used to estimate the concentrations of all the possible complexes
from these molecules in the lower troposphere. At the upper limit
of tetrol concentration, we find that the two diastereomers will bind
to one to three water molecules in high concentrations. However, formation
of sulfuric acid–tetrol–water complexes lead to lower
concentrations, leading us to suggest that these tetrols are unlikely
to be involved in the formation of prenucleation clusters that will
lead to further aerosol growth. Researchers should continue the search
for organic molecules that lead to prenucleation.