Characterizing ultrafine particles and other air pollutants at five schools in South Texas

This study examined five schools with different ventilation systems in both urban and rural areas in South Texas. Total particle number concentration, ultrafine particle (UFP, diameter < 100 nm) size distribution, PM2.5, and CO2 were measured simultaneously inside and outside of various school microenvironments. Human activities, ventilation settings, and occupancy were recorded. The study found a greater variation of indoor particle number concentration (0.6 x 10(3) - 29.3 x 10(3) #/cm(3)) than of outdoor (1.6 x 10(3)-16.0 x 10(3) #/cm(3)). The most important factors affecting indoor UFP levels were related to various indoor sources. Gas fan heaters increased the indoor- to- outdoor ratio (I/O ratio) of total particle number concentrations to 30.0. Foodrelated activities, cleaning, and painting also contributed to the increased indoor particle number concentration with I/O ratios larger than 1.0. Without indoor sources, the I/O ratios for total particles varied from 0.12 to 0.66 for the five ventilation systems studied. The I/O ratio decreased when the outdoor total particle number concentration increased. Particles with diameters <60 nm were less likely to penetrate and stay airborne in indoor environments than larger particles and were measured with smaller I/O ratios.