[1] High HONO level during daytime was observed at a rural site Xinken in southeastern China during the 2004 Program of Regional Integrated Experiments of Air Quality over Pear River Delta (PRIDE-PRD). The high HONO concentration led to a daytime (9:00-15:00) OH formation up to three times faster than that from O 3 photolysis. An unexplained daytime HONO source, approximately four times faster than the reaction of OH with NO, has been derived from the HONO budget estimation. According to current understanding, this unknown source was attributed to heterogeneous reactions of NO 2 on ground and aerosol surfaces. The good correlation between the unknown source and J values is consistent with the photolytic HONO source observed in laboratory studies.

Abstract. To characterize aerosol pollution in Beijing, size-resolved aerosols were collected by MOUDIs during CAREBEIJING-2006 field campaign at Peking University (urban site) and Yufa (upwind rural site). Fine particle concentrations (PM1.8 by MOUDI) were 99.8±77.4 μg/m3 and 78.2±58.4 μg/m3, with PM1.8/PM10 ratios of 0.64±0.08 and 0.76±0.08 at PKU and Yufa, respectively, and secondary compounds accounted for more than 50% in fine particles. PMF model analysis was used to resolve the particle modes. Three modes were resolved at Yufa, representing condensation, droplet and coarse mode. However, one more droplet mode with bigger size was resolved, which was considered probably from regional transport. Condensation mode accounted for 10%–60% of the total mass at both sites, indicating that the gas-to-particle condensation process was important in summer. The formation of sulfate was mainly attributed to in-cloud or aerosol droplet process (PKU 80%, Yufa 70%) and gas condensation process (PKU 14%, Yufa 22%). According to the thermodynamic instability of NH4NO3, size distributions of nitrate were classified as three categories by RH. The existence of Ca(NO3)2 in droplet mode indicated the reaction of HNO3 with crustal particles was also important in fine particles. A rough estimation was given that 69% of the PM10 and 87% of the PM1.8 in Beijing urban were regional contributions. Sulfate, ammonium and oxalate were formed regionally, with the regional contributions of 90%, 87% and 95% to PM1.8. Nitrate formation was local dominant. In summary regional secondary formation led to aerosol pollution in the summer of Beijing.

No abstract

[1] Real-time measurements of ammonia, nitric acid, hydrochloric acid, sulfur dioxide and the water-soluble inorganic aerosol species, ammonium, nitrate, chloride, and sulfate were performed at a pasture site in the Amazon Basin (Rondônia, Brazil). The measurements were made during the late dry season (biomass burning), the transition period, and the onset of the wet season (clean conditions) using a wet-annular denuder (WAD) in combination with a Steam-Jet Aerosol Collector (SJAC). Measurements were conducted from 12 September to 14 November 2002 within the framework of LBA-SMOCC (Large-Scale Biosphere Atmosphere Experiment in Amazonia -Smoke Aerosols, Clouds, Rainfall, and Climate: Aerosols From Biomass Burning Perturb Global and Regional Climate). Real-time data were combined with measurements of sodium, potassium, calcium, magnesium, and low-molecular weight (LMW) polar organic acids determined on 12-, 24-, and 48-hours integrated filter samples. The contribution of inorganic species to the fine particulate mass (D p 2.5 mm) was frequently below 20% by mass, indicating the preponderance of organic matter. The measured concentration products of NH 3 Â HNO 3 and NH 3 Â HCl persistently remained below the theoretical equilibrium dissociation constants of the NH 3 /HNO 3 /NH 4 NO 3 and NH 3 /HCl/NH 4 Cl systems during daytime (RH < 90%). The application of four thermodynamic equilibrium models (EQMs) indicates that the fine mode aerosol anions NO 3 À , Cl À , and SO 4 2À were balanced predominantly by mineral cations (particularly pyrogenic K + ) during daytime. At nighttime (RH > 90%) fine-mode NH 4 NO 3 and NH 4 Cl are predicted to be formed in the aqueous aerosol phase. Probably, Cl À was driven out of the aerosol phase largely by reaction of pyrogenic KCl with HNO 3 and H 2 SO 4 . As shown by an updated version of the equilibrium simplified aerosol model (EQSAM2), which incorporates mineral aerosol species and lumped LMW polar organic acids, daytime aerosol NH 4 + was mainly balanced by organic compounds. -H 2 O aerosol system and its gas phase precursors at a pasture site in the Amazon Basin: How relevant are mineral cations and soluble organic acids?,

No abstract

Continuous measurements of aerosol number size distributions from 3 nm to 10 μm have been first performed within the city area of Beijing since March 2004. Size distributions of the first 45 measurement days (March 05 to April 18, 2004) were investigated in terms of their high variability. Two dust storm events were observed indicated by high number concentrations greater than 1 μm and mass concentrations around 1 mg m−3. Continental highly polluted air was observed during 12 days indicated by a number peak in the accumulation mode range, and submicrometer volume concentrations above 150 μm3 cm−3 were observed. Newly formed particles with more than 100,000 cm−3 were observed on 25 days when the particle surface area concentration drops below a critical value (100–2000 μm2 cm−3) because of clean air from the north. Measurements show only a slight growth (∼1 nm h−1) of the particles indicating that they are produced within the city area of Beijing.

No 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.