Abstract
We conducted intensive observations of ozone, CO, <TEX>$NO_x$</TEX> (=NO and <TEX>$NO_2$</TEX>), <TEX>$NO_y$</TEX> (total odd nitrogen species including particulate nitrate) and total nitrate (the sum of gaseous <TEX>$HNO_3$</TEX> and particulate nitrate) at Cape Hedo, Okinawa, Japan, from 19 March to 3 April, 2009, to investigate ozone production during long-range transport from the Asian continent. Ozone production efficiency (OPE) was used to evaluate photochemical ozone production. OPE is defined as the number of molecules of ozone produced photochemically during the lifetime of a <TEX>$NO_x$</TEX> molecule. OPE is calculated by the ratio of the concentration increase of ozone to that of <TEX>$NO_z$</TEX> (<TEX>$=NO_y-NO_x$</TEX>). Average OPE during observation was estimated to be <TEX>$12.6{\pm}0.5$</TEX>, but concentrations of ozone increased nonlinearly with those of <TEX>$NO_z$</TEX>. This non-linearity suggests that OPE depends on air mass origin and <TEX>$NO_z$</TEX> concentrations. There were very different values of OPE for the same air mass origin, so that only the air mass origin alone does not control OPE. OPE was low when <TEX>$NO_z$</TEX> concentration was high. We examined the correlation between <TEX>$NO_z$</TEX> and <TEX>$CO/NO_y$</TEX> ratios, which we used instead of the ratio of non-methane hydrocarbons (NMHCs) to <TEX>$NO_x$</TEX>. The <TEX>$CO/NO_y$</TEX> ratios decreased with increasing <TEX>$NO_z$</TEX> concentrations. These results indicate that competition reactions of OH with NMHCs and <TEX>$NO_2$</TEX> are the rate determining steps of photochemical ozone production during long-range transport from the Asian continent to Cape Hedo, for high concentrations of nitrogen oxides.
Highlights
Recent remarkable economic progress in East Asia has caused an increase in NOx (=NO + NO2) emissions (e.g. Akimoto, 2003). Ohara et al (2007) developed an emission inventory for Asia (Regional Emission Inven tory in Asia: REAS), and reported that Asian NOx emissions increased by 176% from 1980 to 2003
The air mass around Cape Hedo Atmosphere and Aerosol Monitoring Station (CHAAMS) was well-aged, and these concentration peaks are due to the outflow of Asian pollutants
Average Ozone production efficiency (OPE) was estimated at 12.6±0.5 during the observation period, and it was confirmed that ozone concentration increased nonlinearly with that of NOz
Summary
Recent remarkable economic progress in East Asia has caused an increase in NOx (=NO + NO2) emissions (e.g. Akimoto, 2003). Ohara et al (2007) developed an emission inventory for Asia (Regional Emission Inven tory in Asia: REAS), and reported that Asian NOx emissions increased by 176% from 1980 to 2003. Long-term monitoring of springtime ozone at a site on Mount Happo, Japan, has shown increase at a rate of ~1 ppbv (part per billion by volume) y-1 One reason for this increase is considered to be an indirect effect caused by rapidly increasing anthropo genic emissions of NOx from East Asia (Tanimoto, 2009). An important factor of photochemical ozone production is the NMHCs/NOx ratio, because the ozone production rate is determined with respect to the branching ratio between reactions (7) and (11). To diagnose ozone production during long-range trans port from the Asian continent, we performed intensive observation of NO2 using a laser-induced fluorescence technique at the National Institute for Environmental Studies Cape Hedo Atmosphere and Aerosol Monitoring Station (CHAAMS), Okinawa, Japan. We investigated OPE during the transport using data observed, and discussed the contributing fac tor when determining the value of OPE
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