Gaseous and particulate concentrations of atmospheric boron have been measured simultaneously for the first time at several marine and continental areas using an impregnated filter sampling technique. Rainwater boron concentrations were also determined. The data indicate that most of the atmospheric boron is present in the gas phase. Gaseous boron concentrations are higher over the ocean than over the continents. Particulate boron may have the opposite distribution. Gaseous boron concentrations are elevated in some urban continental areas, probably as a result of volatilization of boron during coal combustion. The concentration of boron in rain and on aerosol particles is similar at all locations, suggesting that scavenging of aerosol particle boron may control boron in rain even though a significant gas phase exists. Total gaseous boron emissions from all sources are estimated as 250-490¿1010 g yr-1, and particulate boron emissions are estimated to be 32--88¿1010 g yr-1. The major global sources of atmospheric boron appear to be volcanic emissions and sea salt aerosol production. The tropospheric residence time of gaseous and particulate boron is estimated to be 19-36 days and 2-6 days, respectively.