Real-time measurements of ammonia, acidic trace gases and water-soluble inorganic aerosol species at a rural site in the Amazon Basin

Abstract

Abstract. We measured the mixing ratios of ammonia (NH 3 ), nitric acid (HNO 3 ), nitrous acid (HONO), hydrochloric acid (HCl), sulfur dioxide (SO 2 ) and the corresponding water-soluble inorganic aerosol species, ammonium (NH, chloride (Cl − ) and sulfate (SO 2− 4 ), and their diel and seasonal variations at a pasture site in the Amazon Basin (Rondônia, Brazil). This study was conducted within the framework of LBA-SMOCC (Large Scale Biosphere Atmosphere Experiment in AmazoniaSmoke Aerosols, Clouds, Rainfall and Climate: Aerosols from Biomass Burning Perturb Global and Regional Climate). Sampling was performed from 12 September to 14 November 2002, extending from the dry season (extensive biomass burning activity), through the transition period to the wet season (background conditions). Measurements were made continuously using a wet-annular denuder (WAD) in combination with a Steam-Jet Aerosol Collector (SJAC) followed by suitable on-line analysis. A detailed description and verification of the inlet system for simultaneous sampling of soluble gases and aerosol compounds is presented. Overall measurement uncertainties of the ambient mixing ratios usually remained below 15%. The limit of detection (LOD) was determined for each single data point measured during the field experiment. Median LOD values (3σ -definition) were ≤0.015 ppb for acidic trace gases and aerosol anions and ≤0.118 ppb for NH 3 and aerosol NH + 4 . Mixing ratios of acidic trace gases remained below 1 ppb throughout the measurement period, while NH 3 levels were an order of magnitude higher. Accordingly, mixing ratios of NH + 4 exceeded those of other inorganic aerosol contributors by a factor of 4 to 10. During the wet season, mixing ratios decreased by nearly a factor of 3 for all compounds comCorrespondence to: I. Trebs (ivonne@mpch-mainz.mpg.de) pared to those observed when intensive biomass burning took place. Additionally, N-containing gas and aerosol species featured pronounced diel variations. This is attributed to strong relative humidity and temperature variations between day and night as well as to changing photochemistry and stability conditions of the planetary boundary layer. HONO exhibited a characteristic diel cycle with high mixing ratios at nighttime and was not completely depleted by photolysis during daylight hours.

Role of ambient ammonia in particulate ammonium formation at a rural site in the North China Plain

“…The morning peak of NH 3 was also observed elsewhere and could have resulted from emissions from fertilised soils and plant stomata, evaporation of dew, human sources, and mixing down of ammonia from the residual layer (Trebs et al, 2004;Norman et al, 2009;Bash et al, 2010;Ellis et al, 2011). Figure 3b reveals that the relative humidity (90-89 %) and temperature (21.5-22.1 • C) remained relatively constant before 06:00 but increased later in the morning.…”

“…Figure 3b reveals that the relative humidity (90-89 %) and temperature (21.5-22.1 • C) remained relatively constant before 06:00 but increased later in the morning. The increasing temperature can heat the Earth's surface and vegetation leaves and reduce the RH, potentially leading to evaporation of NH 3 from soil and plants and volatilisation of ammonium aerosol (Trebs et al, 2004;Norman et al, 2009;Ellis et al, 2011), which may increase NH 3 concentrations in the morning. When the emission was occurring into a shallow boundary layer, NH 3 increase would be more prominent.…”

Chemical characteristics of inorganic ammonium salts in PM<sub>2.5</sub> in the atmosphere of Beijing (China)

“…Thus, the high concentrations of fine particulate NO − 3 in summer period might be due to higher concentrations of NH 3 in the atmosphere available to neutralize H 2 SO 4 and HNO 3 , which is consistent with the observation that the measured particulate species seemed to be neutralized (see below). In addition, the high relative humidity conditions (daily mean 35 %-90 %) in summer period might dissolve a significant fraction of HNO 3 and NH 3 in humid particles, therefore enhancing fine particulate NO − 3 and NH + 4 in the atmosphere (Hesterberg et al, 1996;Krupa, 2003;Trebs et al, 2004Trebs et al, , 2005Guinot et al, 2007;Sciare et al, 2007;Hu et al, 2008;Pathack et al, 2009Pathack et al, , 2011Ianniello et al, 2010;Sun et al, 2010).…”

“…Obviously, NH + 4 was strongly influenced by its gas phase precursor, such as NH 3 , peaking between 08:00 and 10:00 in the morning and revealing much higher concentrations than the anionic species. Possible evaporation of NH 3 from wet surfaces at sunrise, when relative humidities were still high might have caused a significant fraction of gaseous ammonia to dissolve in still humid particles, therefore enhancing particulate NH + 4 (Trebs et al, 2004;Ianniello et al, 2010).…”

Semi-continuous gas and inorganic aerosol measurements at a Finnish urban site: comparisons with filters, nitrogen in aerosol and gas phases, and aerosol acidity

“…In addition, it also measures the concentrations of water-soluble gases that produce ions observable with an IC, using the principles presented, e.g., by Wyers et al (1993). Trebs et al (2004) who used basically the same method, even though they did not call it MARGA then, at a rural site in the Amazon Basin. The instrument consisted of a wet rotating annular denuder in combination with a SJAC, followed by an IC for measuring anions and flow injection analysis (FIA) for measuring ammonium; other cations were not measured.…”