The relationship between real-time and time-integrated coarse (2.5-10 micrm), intermodal (1-2.5 microm), and fine (<2.5 microm) particulate matter in the Los Angeles basin

A periodic review of the National Ambient Air Quality Standards for Particulate Matter by the U.S. Environmental Protection Agency (EPA) will assess the standards with respect to levels, particle size, and averaging times. Some members of the scientific community in the United States and Europe have suggested the use of PM1 instead of PM2.5 as the fine particle measurement standard. This proposed standard is intended to reduce the influence of coarse particle sources on PM2.5, because some evidence suggests that PM1-2.5 is dominated by coarse particulate matter (PM) sources. In this study, coarse (PM2.5-10), intermodal (PM1-2.5), and fine (PM2.5) mass concentrations at four different sites are measured with continuous and time-integrated sampling devices. The main objective is to compare variations in these three size ranges while considering the effects of location, sources, weather, wind speed, and wind direction. Results show strong correlations between PM1 and intermodal PM in receptor sites. The contribution of PM1-2.5 to PM2.5 is highest in the summer months, most likely due to enhanced long-range transport. Coarse PM is poorly correlated with intermodal PM. Continuous data suggest that PM1 is growing into PM1-2.5 via complex processes involving stagnation of the aerosol during high relative humidity conditions, followed by advection during daytime hours.     

Removal of ultrafine and fine particulate matter from air by a granular bed filter

The removal efficiency of granular filters packed with lava rock and sand was studied for collection of airborne particles 0.05-2.5 microm in diameter. The effects of filter depth, packing wetness, grain size, and flow rate on collection efficiency were investigated. Two packing grain sizes (0.3 and 0.15 cm) were tested for flow rates of 1.2, 2.4, and 3.6 L/min, corresponding to empty bed residence times (equal to the bulk volume of the packing divided by the airflow rate) in the granular media of 60, 30, and 20 sec, respectively. The results showed that at 1.2 L/min, dry packing with grains 0.15 cm in diameter removed more than 80% (by number) of the particles. Particle collection efficiency decreased with increasing flow rate. Diffusion was identified as the predominant collection mechanism for ultrafine particles, while the larger particles in the accumulation mode of 0.7-2.5 microm were removed primarily by gravitational settling. For all packing depths and airflow rates, particle removal efficiency was generally higher on dry packing than on wet packing for particles smaller than 0.25 microm. The results suggest that development of biological filters for fine particles is possible.     

Removal of emerging contaminants from wastewater using advanced treatments. A review

Environmental Chemistry Letters - The rise of emerging contaminants in waters challenges the scientific community and water treatment stakeholders to design remediation techniques that are simple,...