Apple's iOS surpassed Google's Android on mobile ad impression share during the first quarter of 2012 according to mobile marketing firm Velti.

At the end of 2011, iOS and Android impressions were evenly represented across Velti's Mobclix Exchange, but as of March 2012, iOS now leads with 53 percent of impressions, compared to Android at 47 percent. Velti adds that iOS commands higher eCPMs (effective cost per thousand impressions) across the board, with iPhone eCPMs almost twice as high as Android. Velti credits the disparity to advertiser demand and preference for iOS.

Fullscreen ad units with rich media features continue to command the highest eCPMs, averaging $1.35 for Apple's iPad, $1.22 for the iPhone and $1.14 for Android devices. Shifting the focus to app categories, weather apps claim the top spot with an average eCPM of $1.24. Education apps follow at $1.17, trailed by lifestyle apps at $0.89 and utilities at $0.68.

Velti adds that Apple's latest iPad, released in early March, captured 2.2 percent of all iPad impressions in its first month after launch. By comparison, the previous iPad 2 claimed 1.5 percent of impressions in its first month of availability.