Mechanisms for the intraseasonal variability of tropospheric ozone over the Indian Ocean during the winter monsoon

Abstract

[1] We synthesize daily sonde (vertical) information and daily satellite (horizontal) information to provide an empirical description of ozone origins over the northern Indian Ocean during the INDOEX (Indian Ocean Experiment) field campaign (February-March 1999). This area is shown to be a significant portion of the ''high-ozone tropics''. East-west O 3 features and their flow are identified, and ozone origins are compared to other tropical regions, using water vapor as a second tracer. In the study period, multiple processes contribute to O 3 column enhancements, their importance varying strongly by latitude: (1) Low-altitude O 3 pollution over the northern Indian Ocean mainly originates from the Indian subcontinent and is traceable to high emission areas.

Atmospheric pollutant outflow from southern Asia: a review

“…-frequently observed free tropospheric layers, usually between 5 and 10 km, with elevated mixing ratios of O 3 and other pollutants; these were originally primarily attributed to long-range transport of polluted air masses from biomass burning in African , although a recent, more detailed analysis (Chatfield et al, 2007) has shown that primary contributions come from stratospheric input of O 3 and from convective lofting of pollutants out of the polluted MBL of the northern Indian Ocean;…”

“…However, two particular criticisms of de Laat (2002) were raised by Mandal (2002): the assumption of an African BMB source is not consistent with the dataset south of the ITCZ, where similar ozone layers were encountered in the UT, but no biomass burning source should be available from Africa (i.e., stratospheric injection must be playing a significant role there); and only a subset (about half) of the available ozone soundings were selected for the analysis, possibly missing important signals in the remaining data. Chatfield et al (2007) also state that though some of their trajectories do originate from the region west of North Africa, none come "close to either lightning or the potential venting of biomass burning." Sorting out this disagreement definitively will make an interesting future topic of research in this area of the field.…”

“…Several studies have also examined various aspects of layers of O 3 pollution observed higher up in the free troposphere. The most comprehensive of these, by Chatfield et al (2007), points towards two primary origins of ozone in the layers above 3-4 km altitude: stratospheric injection (Zachariasse et al, 2000, which provides an additional ∼40-50 nmol/mol of O 3 when this mechanism is active, and convective injection of ozone and its precursors from the low-level SAW-ABC outflow into the middle troposphere over the northern Indian Ocean, which provides an additional ∼20-30 nmol/mol. The analysis of de Laat (2002) provides an alternate explanation for these ozone layers, suggesting, based on model simulations in comparison with ozone soundings, that they originate mainly from convective lofting of biomass burning emissions over Africa.…”

“…-a layer at about 3-4 km altitude which carries pollution primarily from Southeast Asia, especially from biomass burning Chatfield et al, 2007),…”

An upper tropospheric ‘ozone river’ from Africa to India during the 2008 Asian post-monsoon season

“…De Laat, 2002;Chatfield et al, 2007;Lawrence and Lelieveld, 2010). In particular, O 3 peaks reaching 120 ppbv were often found in the UT within layers 1Á2 km thick just below the tropopause (De Laat et al, 1999).…”