Obligatory reminder that the NASA Clean Air Study on indoor plants was not conducted under realistic home or office conditions, and follow-up studies have shown mixed results at best.

Adding a few plants to a room that's not hermetically sealed (let alone a huge open-concept office space) will not have any practical impact on air quality, be it oxygen levels or pollutant concentration. It'll make your space look good, though.

Further reading:

https://en.wikipedia.org/wiki/NASA_Clean_Air_Study

http://time.com/5105027/indoor-plants-air-quality/