Here are the key points:
1. Wood smoke (and possibly cooking smoke) is likely the largest direct contributor (i.e., emitted from a source) to PM2.5 on winter days with PM2.5 > 20 ug/m3. Note that our PM2.5 comes from these direct emissions and from chemical reactions involving other gases generated by combustion (such as nitrogen oxide). The latter are typically referred to as secondary PM2.5.
2. Wood burning emissions are highly variable depending on their design, operations, and fuel, but they are far filthier than heating with natural gas.
|Source: Kelly et al. (2013) presentation|