Water soluble inorganic trace gases and related aerosol compounds in the tropical boundary layer. An analysis based on real time measurements at a pasture site in the Amazon Basin

This dissertation investigates the behavior of water-soluble inorganic trace gases and related aerosol species in the tropical boundary layer. Mixing ratios of ammonia (NH3), nitric acid (HNO3), nitrous acid (HONO), hydrochloric acid (HCl), sulfur dioxide (SO;,) and the corresponding water-soluble aerosol species, ammonium (NH,,1), nitrate (NO3 ), nitrite (NO,), chloride (CI) and sulfate (SO,") were measured at a pasture site in the Amazon Basin (Rondónia, Brazil). Sampling was performed from 12 Sep. to 14 Nov. 2002, covering the late dry (biomass burning) season, the transition period and the onset of the wet season (clean conditions) (LBA-SMOCC*). Measurements were made continuously using a wet-annular denuder (WAD) in combination with a Steam-Jet Aerosol Collector (SJAC) followed by on-line analysis. Real-time data were combined with measurements of the aerosol compounds sodium (Na+), potassium (K), calcium (Ga ), magnesium (Mg2) and low-molecular weight polar organic acids determined using integrated filter samples. Additionally, on-line measured mixing ratios of nitric oxide (NO), nitrogen dioxide (NTX) and ozone (O3) as well as (microj-meteorological quantities are considered, Gaseous NH3 was present in mixing ratios an order of magnitude higher than those of HN0:i, HONO, HCl and SO,. Thermodynamic equilibrium models are used to explore the impact of mineral cations (particularly pyrogenic K+) and LMW polar organic acids on the NH4+-NO3"-C1 -SO.," -H2O aerosol system. Mineral cations present in Amazonian fine mode aerosols significantly balanced aerosol NO.," and SO/ during daytime and (NH4)2SOj appeared to be only a minor aerosol component. Thermodynamic equilibrium permitted the formation of aqueous ??,,??;, and NH^Cl only during nighttime at RH>90 %. During daytime, excess NH3 neutralized LMW polar organic acids, forming aerosol NRy. Local dry and wet deposition rates of inorganic ? are presented. Dry ? deposition was inferred using the "big leaf multiple resistance approach" and a canopy compensation point model. Dry ? deposition is dominated by NH:i and NO3, which featured highest mixing ratios as a consequence of biomass burning activities during the dry season. The pasture site was likely to have a strong potential for daytime NH3 (re-) emission, owing to high canopy compensation points, which are related to high surface temperatures and to direct NH^ emissions from cattle excreta. Total (dry + wet) ? deposition was estimated to be 7.3 - 9.8 kgN ha"1 yr"\ which exceeds predictions for the Amazon region by global chemistry and transport models by at least factor of two.