Ambient ozone (O3) in three Class I wilderness areas in the northeastern USA: Measurements with Ogawa passive samplers

Ambient ozone (O3) was measured in two Class I wilderness areas, one within the White Mountain National Forest in north central New Hampshire (NH) and one within the Green Mountain National Forest in southwestern Vermont (VT), for six weeks between 5 July and 16 August 1994, using Ogawa passive nitrite-coated filter samplers and a one week exposure period each time. Results for 7-day mean ambient O3 concentrations from the passive samplers were compared to results from a co-located continuous ultraviolet photometric O3 analyzer both in NH and VT. Although the size of the data set was small, agreement through simple linear regression between mean 7-day O3 concentrations determined by the continuous monitors, and those obtained from the passive samplers was generally very good (adjusted R2 = 0.759; P = 0.0003). Overall, excluding the one outlier value, any observed differences in the results obtained by the two methods when comparing co-located passive samplers to the continuous monitor within a given study location, appeared to be solely due to experimental error.