To evaluate and validate microAeth for use as fixed site monitor, side-by-side testing of several microAeth units and comparisons of the microAeth units with other established BC measurement methods, including a rack-mount Aethalometer and multi-wavelength optical measurements on integrated Teflon filters, were conducted. Of particular note the multi-wavelength optical measurement of BC is calibrated gravimetrically by collecting, weighing and then optically measuring PM2.5 filters of kerosene soot and assuming that 100% of the mass is BC (Yan et al., 2011 ); literature values consistently show values of 95% ± 5% (Lam et al., 2012 (link)). This comparison testing was conducted from the window of a fifth floor apartment along the W168th street, NYC, which is situated at an intersection of a busy street with idling ambulances and a truck route with heavy traffic. However, the sampling window faced a courtyard rather than the street. Six microAeth units were inside the apartment; sampling tubing passed through a window board, and the sampling inlets were about 0.3 m from the outside wall. MicroAeths were set to acquire BC data for every 1 min at a flow rate of 100 mL/min and replace the filter for every 24 hrs.
In a separate experiment, four of six microAeth units were operated in turn along with a rack-mount Aethalometer® (AE22, Magee Scientific Co.) continuously measuring BC level every minute at the flow rate of 4.0 LPM and three integrated PM2.5 samplers (KTL cyclones BGI, Inc.) collecting PM2.5 on 37 mm Teflon membrane filters (Pall Corporation, Port Washington, NY) at flow rate of 4.0 LPM. This comparison test ran for four weeks with three consecutive 24-hr sampling periods every week. The full size Aethalometer used a web-reinforced quartz fiber filter tape (supplied by Magee Science Co.), allowing an automatic advance of the filter when the sampling spot became heavily loaded.
A multi-wavelength optical method has been established for measuring BC levels collected on PM2.5 Teflon filters via optical equipment purchased from Ocean Optics (Dunedin, FL) including a balanced deuterium tungsten halogen light source (DH-2000-BAL), an integrating sphere (ISP-50-8-R) modified to have a reflective white bottom, a lab-made filter holder, and an Ocean Optics USB4000-VIS-NIR fiber-optic spectrometer (Yan et al., 2011 ). Whereas the microAeth and full size Aethalometer measures the change in light attenuation between every time stamp (e.g., each min), from which the BC air concentration is calculated for that period of time, the multi-wavelength optical reflectance method determines the total BC mass loading on filters (based on an empirical gravimetric calibration) that occurred over the entire deployment period, which was 24 hrs in this experiment. For comparison, data retrieved from both microAeth and full size Aethalometer in the 24 hours period were integrated and the daily average BC level were compared to those measured by the multi-wavelength method. The high resolution temporal data from both microAeth and Aethalometer was compared with each other; data from a single random day was selected to better illustrate details.
In a separate experiment, four of six microAeth units were operated in turn along with a rack-mount Aethalometer® (AE22, Magee Scientific Co.) continuously measuring BC level every minute at the flow rate of 4.0 LPM and three integrated PM2.5 samplers (KTL cyclones BGI, Inc.) collecting PM2.5 on 37 mm Teflon membrane filters (Pall Corporation, Port Washington, NY) at flow rate of 4.0 LPM. This comparison test ran for four weeks with three consecutive 24-hr sampling periods every week. The full size Aethalometer used a web-reinforced quartz fiber filter tape (supplied by Magee Science Co.), allowing an automatic advance of the filter when the sampling spot became heavily loaded.
A multi-wavelength optical method has been established for measuring BC levels collected on PM2.5 Teflon filters via optical equipment purchased from Ocean Optics (Dunedin, FL) including a balanced deuterium tungsten halogen light source (DH-2000-BAL), an integrating sphere (ISP-50-8-R) modified to have a reflective white bottom, a lab-made filter holder, and an Ocean Optics USB4000-VIS-NIR fiber-optic spectrometer (Yan et al., 2011 ). Whereas the microAeth and full size Aethalometer measures the change in light attenuation between every time stamp (e.g., each min), from which the BC air concentration is calculated for that period of time, the multi-wavelength optical reflectance method determines the total BC mass loading on filters (based on an empirical gravimetric calibration) that occurred over the entire deployment period, which was 24 hrs in this experiment. For comparison, data retrieved from both microAeth and full size Aethalometer in the 24 hours period were integrated and the daily average BC level were compared to those measured by the multi-wavelength method. The high resolution temporal data from both microAeth and Aethalometer was compared with each other; data from a single random day was selected to better illustrate details.
