I travelled a few times to China (Hangzhou, Chengdu, Guangzhou) and one big issue the smogg: the foggy/smoky conditions which prevent a good contrast and lead to dull photographs. After some trials with a few lenses, I found that the kit lens and the all-around lenses (DA18-250mm/DA18-135mm) are not good enough in many situations, unless the sun shines.
In my experience, I tend to favor a prime lens, the Voigtlander Nokton 58mm f1.4, for this type of smoggy conditions, over all other lenses, even if the focal length is not right. I share some toughts on the VL58mm f1.4 at:
https://www.pentaxforums.com/forums/10-pentax-slr-lens-discussion/209251-fa31...mm-f1-4-a.html
To sum up, I would recommend to travel light, possibly with one WR lens for the heavy rain (and the sunshine) and the VL58mm f1.4mm for the poor lighting conditions like smogg.
Hope that the comment may help.
Last edited by hcc; 02-27-2014 at 02:10 AM.