Indoor PM 2.5 and its morphology in a naturally ventilated office in Xi'an, China.

This study aims to investigate the relationships of sample, morphology, and mineralogy with indoor and outdoor PM2.5during a heating period and a nonheating period. Indoor (a naturally ventilated office) and outdoor (adjacent courtyard) PM2.5concentrations were continuously monitored in Xi'an, China from June 1, 2015 to January 7, 2016. The average indoor and outdoor PM2.5concentrations during the heating period were 169 and 224 μg/m3respectively, whereas the corresponding PM2.5for the nonheating episode were 59 and 66 μg/m3. The indoor/outdoor ratio and infiltration factor revealed that PM2.5had primarily outdoor sources. Morphology, elemental composition, and mineralogy of PM2.5collected indoors and outdoors were studied using scanning electron microscopy coupled with energy dispersive spectrometry (SEM-EDS) and X-ray diffraction (XRD). The SEM micrograph of PM2.5collected during the heating period was different from that collected during the nonheating period both indoors and outdoors. EDS spectra indicated that C- and O-rich particles dominated over other elements regardless of the sampling period or place and the indoor PM2.5consists mainly of earth crustal materials. Based on the XRD analysis, indoor PM2.5was mostly made up of amorphous compounds while outdoor PM2.5contained some crystalline materials such as quartz, hematite, and calcium carbonate. [ABSTRACT FROM AUTHOR]