A pervasive role for biomass burning in tropical high ozone/low water structures.

Air parcels with mixing ratios of high O3 and low H2O (HOLW) are common features in the tropical western Pacific (TWP) mid-troposphere (300-700 hPa). Here, using data collected during aircraft sampling of the TWP in winter 2014, we find strong, positive correlations of O3 with multiple biomass burning tracers in these HOLW structures. Ozone levels in these structures are about a factor of three larger than background. Models, satellite data and aircraft observations are used to show fires in tropical Africa and Southeast Asia are the dominant source of high O3 and that low H2O results from large-scale descent within the tropical troposphere. Previous explanations that attribute HOLW structures to transport from the stratosphere or mid-latitude troposphere are inconsistent with our observations. This study suggest a larger role for biomass burning in the radiative forcing of climate in the remote TWP than is commonly appreciated.

Source location of air pollution and cardiac autonomic function: trajectory cluster analysis for exposure assessment.

Although many studies report that exposure to air pollution harms health, few have examined associations between pollution sources and health outcomes. We hypothesized that pollution originating in different locations has different associations with heart rate variability (HRV) among 497 men from the Normative Aging Study in Boston, Massachusetts. We identified the paths that air masses traveled ('back-trajectories') before arriving in Boston on the days the men were examined. Next, we classified these trajectories into six clusters. We examined whether the association of measured air pollutants with HRV (standard deviation of normal-to-normal intervals, high-frequency power (HF) and low-frequency power (LF), and LF/HF ratio) differed by cluster. We also examined whether the clusters alone (not considering air pollution measurements) showed different associations with HRV. The effects of black carbon (BC) on all HRV measures were strongest on days with southwest trajectories. Subjects who were examined on days where air parcels came from west had the strongest associations with ozone. All particle pollutants (particulate matter <2.5 microm in aerodynamic diameter (PM2.5), BC, and sulfates) were associated with increased LF/HF ratio on days with relatively short trajectories, which are related to local, slow-moving air masses. We also observed significant increases in LF/HF in days where air came from the northwest and west, compared to north trajectory days. Health effects associated with exposure to air pollution can be evaluated using pollutant concentrations as well as aspects of the pollution mixture captured by identifying locations where air masses originate. Independent effects of both these indicators of pollution exposure were seen on cardiac autonomic function.