Surface ozone enhancements in the south of Brazil owing to large-scale air mass transport

Surface ozone mixing ratios were monitored in the north-west region of the state of Parana (at a site near the city of Maringa, 23.1°S, 53.1°W), from August 2001 to November 2002, in a specific experiment to determine the impact of large-scale transport, over a region of small biomass burning activity (non-source regions). Surface ozone measurements, backward trajectories and meteorological conditions were used to determine the influence of large-scale transport. Surface ozone enhancements were observed when the anticyclonic circulation was well defined and the air masses came from significant source regions of biomass burning (states of Tocantins, Para, Mato Grosso and Mato Grosso do Sul). An example of such enhancement is obtained between 25 and 31 August 2001, when the measured average ozone mixing ratio was 89 parts per billion by volume (ppbv) ± 7.4, with maximum values between 93 and 173 ppbv. Comparison of this and the background concentration during the wet season (January, for example) shows a significant enhancement of 76 ppbv. During the same month, but under the influence of a different transport regime, 8–24 August 2001, considerably lower values were measured (47.2±7.2 ppbv).