A good, easy, informative read on engine lubrication. http://infohouse.p2ric.org/ref/31/30453.pdf

Bottom line on particle size wear is to use filtration that is good below the <20u range particle size & change the oil before the base number is depleted to control corrosive chemical wear.

UOA = Used Oil Analysis with particle counts, can determine how both of those parameters are doing for our particular engine in it's use/drive cycle/OCI =Oil Change Interval & FCI = Filter Change Interval, with the specified, or chosen lube & filtration products.

Short tripping, stop & go city driving, where the engine or oil don't get up to full operating temperature, or not for very long if they do manage to warm up, is Severe Service & in cold weather is even more severe & calls for more frequent oil & filter changes as our Owner Manual calls out.