Sulfate Formation via Cloud Processing from Isoprene Hydroxyl Hydroperoxides (ISOPOOH)

Area of Science:

• Atmospheric Chemistry
• Environmental Science

Background:

• Sulfur dioxide (SO2) oxidation in cloudwater forms sulfate, a key component of particulate matter (PM).
• Hydrogen peroxide (H2O2) is the primary oxidant, but multifunctional organic hydroperoxides are increasingly recognized for their atmospheric importance.
• Previous research focused on monofunctional organic peroxides, leaving a gap in understanding multifunctional hydroperoxide roles.

Purpose of the Study:

• To investigate the aqueous oxidation of sulfur dioxide (SO2) by isoprene hydroxyl hydroperoxide (ISOPOOH) isomers.
• To compare the reactivity of ISOPOOH with hydrogen peroxide (H2O2) in SO2 oxidation under cloud conditions.
• To assess the atmospheric significance of ISOPOOH-driven sulfate formation, particularly in isoprene-rich, low-NOx environments.

Main Methods:

• Experimental investigation of SO2 oxidation kinetics by ISOPOOH isomers at cloud-relevant pH (3-6).
• Utilized Henry's law constants to determine the abundance and partitioning of ISOPOOH in cloudwater.
• Incorporated new reaction mechanisms into the GEOS-Chem atmospheric model for simulation.

Main Results:

• Isoprene hydroxyl hydroperoxide (ISOPOOH) isomers demonstrate significant reactivity in oxidizing SO2 in cloudwater.
• The contribution of ISOPOOH to sulfate formation is comparable to or exceeds that of H2O2 under specific atmospheric conditions.
• pH dependence studies confirmed the importance of these reactions within the typical cloud pH range.

Conclusions:

• Multifunctional hydroperoxides, specifically ISOPOOH, play a critical role in atmospheric sulfate production.
• These pathways are particularly important in regions with high isoprene emissions and low-nitrogen oxide (NOx) conditions.
• Updated atmospheric models highlight the need to include ISOPOOH chemistry for accurate sulfate formation predictions.