Woods et al. just published an article in JVGR regarding the impact of ash particle size and shape on electrical conductivity: 
https://authors.elsevier.com/c/1aW5C1LkU3S0v6

​A new analysis of the shocks produced from lightning discharge and the textural effects on ash particles was recently published in EPSL: 
​https://authors.elsevier.com/a/1aXAY,Ig4KpY2