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

2. Investigation of longer-term averages

3. Estimation of longer-term HF averages
One-hour 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

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

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

6. 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

7. 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

8. 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