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 (NH3), nitric acid (HNO3), nitrous acid (HONO), hydrochloric acid (HCl), sulfur dioxide (SO2) and the corresponding water-soluble inorganic aerosol species, ammonium (NH4+), nitrate (NO3−), nitrite (NO2−), chloride (Cl−) and sulfate (SO42−), 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 Amazonia Smoke Aerosols, Clouds, Rainfall and 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 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 NH3 and aerosol NH4+. Mixing ratios of acidic trace gases remained below 1ppb throughout the measurement period, while NH3 levels were an order of magnitude higher. Accordingly, mixing ratios of NH4+ 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 compared 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.

Physical and chemical characterization of ambient aerosol by HR‐ToF‐AMS at a suburban site in Hong Kong during springtime 2011

“…MARGA uses a wet rotating denuder to absorb gases from the sampled air and a steam jet aerosol collector to retrieve particulate matter. Two ion chromatography systems are used for species separation and yield analytical data for both cations and anions [Trebs et al, 2004]. The size cut for the AMS is roughly 1 μm due to the limitations of the AMS lens system, while MARGA has a size cut of 2.5 μm.…”

Aerosol Inorganic Composition at a Tropical Site: Discrepancies Between Filter-Based Sampling and a Semi-Continuous Method

“…Measurement intervals were 20 min (biomass burning season), 40 min (transition period), and 60 min (wet season). Measurement uncertainties were estimated to remain below 15% (Trebs et al 2004). A detailed description of the WAD/SJAC system and the analytical procedures is given elsewhere (Slanina et al 1992;Slanina et al 2001;Trebs et al 2004).…”

“…The sampled air was then drawn through a PFA Teflon tubing connection to the sampling system in an air conditioned laboratory. During the field experiment, the steel elbow was replaced periodically with a pre-impactor (PM 2.5 size cut; type 413, University Research Glassware), such that aerosol samples of either PM 2.5 or total suspended particulate matter (TSP) were collected in alternating cycles (1-3 days) (Trebs et al 2004;Trebs et al 2005). Aerosol particles were collected using a Steam-Jet Aerosol Collector (SJAC) (Khlystov et al 1995).…”

“…The air flow in the conduit was generated by a suction fan in the conduit bottom. A sub-sample of the air was aspirated from the center of the conduit's cross section area at a flow rate of ∼17 l min −1 (STP: 298.15 K and 1000 hPa) through a steel elbow (Trebs et al 2004). The sampled air was then drawn through a PFA Teflon tubing connection to the sampling system in an air conditioned laboratory.…”

“…Currently, this is the only available approach for collecting gas and aerosol species simultaneously and selectively with high time resolution. The first semi-continuous measurements of aerosol , Cl -, NH + 4 , and SO [2][3][4] and their gaseous precursors HNO 3 , HCl, NH 3 , and SO 2 in a tropical environment were made in southwestern Amazonia (Rondônia, Brazil) within the framework of the LBA-SMOCC 2002 campaign (Large Scale Biosphere Atmosphere Experiment in Amazonia, Smoke Aerosols, Clouds, Rainfall and Climate: Aerosols from Biomass Burning Perturb Global and Regional Climate) Trebs et al 2004). Measurements were conducted using a wet-annular denuder (WAD) in combination with a Steam-Jet Aerosol Collector (SJAC) (Slanina et al 2001).…”