The atmospheric fate of cashmeran from musk-smelling volatile chemical products (VCPs) in chamber, indoor, and outdoor environments

Synthetic musk compounds, like cashmeran, are a group of semi-volatile organic compounds commonly used as fragrances in perfumes. In addition to being potential indoor pollutants, they are also regarded as emerging outdoor pollutants, known at volatile chemical products (VCPs). Cashmeran is a bicyclic synthetic musk compound, and a major component of a commercial perfume for men. Here, we aim to better predict the atmospheric fate of cashmeran indoors and outdoors using a Vocus proton transfer time-of-flight mass spectrometer.

Using the Vocus, we show that cashmeran was the dominant musk in a commercial perfume among other musk compounds like galaxolide, astratone, and rosamusk. Next, we measured the rate constant of cashmeran (C₁₄H₂₂O) with ozone for the first time under different experimental conditions to probe its ozonolysis mechanism. In the absence of O₂, we calculated a rate constant of (2.78 ± 0.31) x 10^-19 cm³mol^-1s^-1 at (293 ± 1) K and observed the formation of C₁₄H₂₂O₂ as the key oxidation production. The ozonolysis reaction in the absence of O₂ did not generate SOA. In the presence of O₂, preliminary results show the rate constant to be 5.00 x 10^-18 cm³mol^-1s^-1 at 293 K and the ozonolysis reaction formed SOA with a mass yield of 121 µg m^-3. The rate constant observed in the presence of O₂ indicate the importance of key carbon-radical chemistry and impact of partitioning sinks in understanding the fate of this molecule in the atmosphere. We hypothesize that the slow oxidation of cashmeran with ozone makes loss to partitioning to aerosols a competitive sink in determining its fate.

Furthermore, we investigated how partitioning sinks might be competitive to gas-phase oxidation for the fate of cashmeran from a commercial perfume in an office environment. We show that partitioning to cotton is the major sink, suggesting this molecule can be easily transported outdoors by humans and their clothing.

We further tested this hypothesis during THE CIX urban field campaign in Toronto, Canada in July-August 2023. We detected cashmeran outdoors throughout the campaign up to 10 ppt. As expected from a fragrant VCP, cashmeran peaked during the week only and in the morning. Based on our findings, we conclude that musk compounds, like cashmeran, are long-lived SVOCs capable of impacting urban air quality.