Distribution characteristics of methylsiloxanes in atmospheric environment of Saitama, Japan: Diurnal and seasonal variations and emission source apportionment

The large production volume of methylsiloxanes (MSs), combined with their high mobility/volatility and persistence, is a matter of concern from the atmospheric pollution perspective. Therefore, we evaluated of the concentrations and emission sources of MSs, including 7 cyclic methylsiloxanes (D3-D9; CMSs, the number refers to the number of Si-O bonds) and 13 linear methylsiloxanes (L3-L15; LMSs) in ambient air collected from Saitama, Japan. This is a first study regarding the evaluation of 20 methylsiloxanes in the Japanese atmosphere. We improved the air sampling methodology by determination the stability of D5 during a 7-d air sampling and arbitrary sample storage period using polystyrene-divinyl benzene copolymer sorbent (Sep-Pak plus PS-2). We analyzed air samples for MSs seasonally collected from nine locations in Saitama, including urban, suburban, rural, and mountainous areas. The mean CMS and LMS concentrations were 358 ng m^-3 and 13.4 ng m^-3, respectively. The D5 concentrations were distributed widely, with high concentrations in urban/suburban populous areas and dispersed at low concentrations in surrounding areas (north and mountainous areas). We analyzed 7-d air samples collected every week over a year and found apparent seasonal and periodic trends in the CMS concentrations. In the diurnal sampling campaign, we observed periodic fluctuations in ambient CMSs, with an inverse relationship with the atmospheric boundary layer development during the day. Backward trajectories and the prevailing wind direction during the sampling period indicated that the specific profiles of D4 observed in fall/winter weeks and north of Saitama could be ascribed to northwestward air-mass advection. We employed a novel approach in estimating CMSs emission sources and source apportionment by using non-negative matrix factorization (NMF). The concentration matrix was divided successfully into two factors (emission sources) namely, personal care and household products and industrial activities.