There was a very good, and detailed article on acidity in Roast Magazine a while back. Actually talking about perceived acidity in Robusta vs. Arabica is not quite as simple as you would think. Processing methods etc play a part, as do the roast processes. Acidity as such (and I do not have the mag in front of me so I am going from my failing memory here)
The main "acids" in a typical cup are-
Lactic Acid
Acetic Acid
Citric Acid
Malic Acid
Phosphoric
Quinic Acid
Chlorogenic
Palmitic Acid
Linoleic Acid
Perceived "acidity" can be both a good and a bad trait. For instance in espresso too much acidity is not desirable, while in other preperations it is a positive trait. Some of the acid types- Malic for instance- are also found in grapes- wine preperation.
Anyway...I am off track here. Robusta generally has more, not less of these acids tahn arabica. A wet processed Arabica, will have up to twice as much compound acid per dry weight, tahn dry processed arabica from the same collection area. The grind (finer=more), the brewing time (longer=more) and the tempertaure (hotter=more) all play a big factor in acidity in a cup of coffee.
Robusta vs. Arabica- at the end of the day preference will nearly always be in part a cultural one (ie- in Indonesia the last 100 years have been robusta-robusta-robusta for local consumption). But I guess with the big differences in Arabica and Robusta, from a DNA and genetic point of view-means Arabica is always going to have the flavor, aroma, body advantages even over a washed and well prepped Robusta. :grin: