Until looking through the code, I had thought Atom was using Microsoft's WPF graphics rendering interface for the GUI. In which case the solution is simply setting the text-formatting option to "Display" rather than the default "Ideal".

www.hanselman.com/blog/WPFAndTextBlurrinessNowWithCompleteClarity.aspx

I don't know what's causing blurry fonts on Atom, but it's certainly not my system configuration to blame; I'm not using any unusual settings/hardware; default DPI with a 1440x900 display. Other software (Notepad++, Visual Studio, Eclipse, etc) render fonts just fine.