Atmospheric Ozone, Mercury, and Biomass Burning in South-Central Texas
Liu, Lei 1989-
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This study investigated atmospheric ozone, mercury, and biomass burning characteristics in south-central Texas. I examined the past twenty-three years of ground-level O3 data and selected meteorological parameters in Houston, and found the frequency of southerly flow has increased by a factor of ~2.5 over the period 1990–2013, likely suppressing O3 photochemistry and leading to a “cleaner” Houston environment. The sea breeze was enhanced greatly from 1990 to 2013 due to increasing land surface temperatures, increased pressure gradients, and slightly stronger on-shore winds. Long-term continuous measurements of atmospheric mercury, meteorological parameters, and key trace gases were conducted in Houston, Texas under urban and coastal marine settings. At the urban site, gaseous elemental mercury (GEM) mean value was 185 ppqv and 165 ppqv at the coastal site. The urban site had a greater occurrence of high mercury events than the coastal site. A variable mercury diurnal pattern was found: At the urban site, GEM showed a maximum mixing ratio before sunrise and the minimum mixing ratio in late afternoon. At the coastal site, GEM decreased at night and reached its minimum before sunrise. The relationship between mercury species and meteorological factors was studied. The concurrence of GEM, CO2, CO, CH4, and SO2 maximum values were striking. A prescribed grassland fire experiment was conducted employing in-situ field sampling combined with comprehensive pre-burn and post-burn sampling. The volatile organic compounds (VOCs) exhibited a double peak feature in the flaming and smoldering stages. The emission of VOCs was associated primarily with the smoldering combustion stage and correlated better with CO than with CO2. The emission factors of CO2, CO, CH4, NO, CH3Cl, C2H6, C2H4, C3H8, C3H6, C6H6, and C7H8 accounted for 96% of the total species. Total gaseous mercury was released primarily during the smoldering phase, although the total amount released from the fire was small (0.015 kg). Overall, 53,257 kg CO2 was emitted into the atmosphere during the fire and it accounted for 95% of all species emissions. The relationship between carbon emissions from the dry fuel (194 tons) and released from CO2 (14.5 tons) was found to be 7.5% for this event.