Responses to questions about HF modeling Mike Williams January 17, 2014

Investigation of longer-term averages

Estimation of longer-term HF averages One-hour 24-hour Annual (2012) 7.5 μg/m3 5.2 μg/m3 3.8 μg/m3 .40 μg/m3 .65 μg/m3 .15 μg/m3 .025 μg/m3 .15 μg/m3 .18 μg/m3 μg/m3 represents micrograms per cubic meter

Locations of Maximum one-hour, 24 hour, and annual HF concentrations 24-HR 1-HR

The Role of Precipitation in Air Dispersion Mike Williams Jan. 17, 2014

Major Factors Neutral or unstable atmospheric stability enhances vertical spread of plume and reduces ground-level concentrations Rain or snow collects soluble gases and deposits them on the ground and reduces air concentrations

Effects on stability Cloud tops cool the air so that it sinks and causes air next to surface to mix upward during nighttime conditions heat Cloud top Ground

Cleaning effect of precipitation Soluble gases such as HF are absorbed into snowflakes or rain droplets Small droplets or particles are collected by falling droplets or snowflakes The same processes are used to scrub pollutants from the stack gasses in the scrubbers