Variation in indoor particle number and PM 2.5 concentrations in a radio station surrounded by busy roads before and after an upgrade of the HVAC system

Abstract

Indoor particle number and PM 2.5 concentrations were investigated in a radio station surrounded by busy roads. Two extensive field measurement campaigns were conducted to determine the critical parameters affecting indoor air quality. The results indicated that indoor particle number and PM 2.5 concentrations were governed by outdoor air, and were significantly affected by the location of air intake and design of HVAC system. Prior to the upgrade of the HVAC system and relocation of the air intake, the indoor median particle number concentration was 7.4×10 3 particles/cm 3 and the median PM 2.5 concentration was 7 μg/m 3. After the relocation of air intake and the redesign of the HVAC system, the indoor particle number concentration was between 2.3×10 3 and 3.4×10 3 particles/cm 3, with a median value of 2.7×10 3 particles/cm 3, and the indoor PM 2.5 concentration was in the range of 3–5 μg/m 3, with a median value of 4 μg/m 3. By relocating the air intake of the HVAC, the outdoor particle number and PM 2.5 concentrations near the air intake were reduced by 35% and 55%, respectively. In addition, with the relocation of air intake and the redesign of the HVAC system, the particle number penetration rate was reduced from 42% to 14%, and the overall filtration efficiency of the HVAC system (relocation of air intake, pre-filter, AHU and particle losses in the air duct) increased from 58% to 86%. For PM 2.5, the penetration rate after the upgrade was approximately 18% and the overall filtration efficiency was 82%. This study demonstrates that by using a comprehensive approach, including the assessment of outdoor conditions and characterisation of ventilation and filtration parameters, satisfactory indoor air quality can be achieved, even for those indoor environments facing challenging outdoor air conditions.