Volatile methylsiloxanes in a textile dyeing and printing industrial park: Source profiles, ambient distributions and...

Volatile methylsiloxanes (VMSs) are emerging secondary organic aerosol (SOA) precursors, but their industrial emissions remain poorly quantified. Here we characterize 17 VMSs (cyclic D3 -D10 and linear L2 -L10) measured by thermal desorption-gas chromatography-mass spectrometry in a modern textile dyeing and printing industrial park in Guangdong, China. Sampling covered production processes, exhaust outlets of seven factories, the centralized wastewater treatment plant (WWTP), and ambient sites from factory boundaries to park boundaries and nearby residential areas. Total VMSs ranged 22.21 -1190.98 μg·m⁻³ in production areas and 86.35-6981.93 μg·m⁻³ in exhaust outlets, confirming textile dyeing and printing as significant industrial VMS sources. Production stages were enriched in higher linear VMSs (L8-L9), whereas exhaust was dominated by D3-D6 with appreciable L7. The WWTP off-gas averaged 3141.01 ± 480.03 μg·m⁻³, dominated by D3-D5. In surrounding ambient air, cyclic VMSs were 1.39-22.27 μg·m⁻³ and linear VMSs were 0.62-73.43 μg·m⁻³, decreasing from industrial boundaries to residential sites. D4 and D5 were strongly correlated (R² = 0.84), and the D4/D5 ratio increased downwind, consistent with atmospheric dispersion and preferential loss of D5. Using literature SOA yields with conservative substitutions, the total ambient VMS-derived SOA formation potential was estimated to range from 0.07 to 1.05 μg·m⁻³, with D3, D5, and L7-L10 contributing most. These results identify textile dyeing/printing and associated WWTPs as substantial industrial VMS sources with measurable SOA impacts, highlighting the need to include VMSs, particularly linear VMSs, in industrial emission inventories and SOA-oriented assessments.