Sniff AirTraffic using Macbook is easy and you just have to follow the steps below:
1.)Quit all open applications.
2.)Try to join the Wi-Fi network that you are having issues with if you are not already connected.
3.)Open Wireless Diagnostics. Tip: You can hold down the Option key and then click the Wi-Fi menu extra.
4.)Enter your admin name and password when prompted.
5.)In Wireless Diagnostics, choose Window > Sniffer,
5.)Choose appropriate channel and channel width as per your Wireless AP Radio configuration
2.)Try to join the Wi-Fi network that you are having issues with if you are not already connected.
3.)Open Wireless Diagnostics. Tip: You can hold down the Option key and then click the Wi-Fi menu extra.
4.)Enter your admin name and password when prompted.
5.)In Wireless Diagnostics, choose Window > Sniffer,
5.)Choose appropriate channel and channel width as per your Wireless AP Radio configuration
Start the capture , click stop when you are done , A capture file will be placed on the desktop.
I also found a Video done my benmiller regarding the same:
http://www.sniffwifi.com/2013/10/how-to-capture-wifi-free-in-mac-os-x.html
Journey in Cyber Security and Wi-Fi Engineering 