Secondary inorganic aerosol chemistry and its impact on atmospheric visibility over an ammonia-rich urban area in Central Taiwan. (1st November 2022)

• Record Type: Journal Article
• Authors: Young, Li-Hao; Hsiao, Ta-Chih; Griffith, Stephen M.; Huang, Ya-Hsin; Hsieh, Hao-Gang; Lin, Tang-Huang; Tsay, Si-Chee; Lin, Yu-Jung; Lai, Kuan-Lin; Lin, Neng-Huei; Lin, Wen-Yinn
• Is Part Of: Environmental pollution. Volume 312(2022)
• Publication Date: 2022-11-01
• Subjects: Aerosol chemistry -- Inorganic salts -- Light extinction -- Thermodynamic equilibrium -- Gas-particle partition -- Control strategy; ALWC Aerosol liquid water content -- BAM β-ray attenuation monitor -- IGAC In-situ Gas and Aerosol Composition -- PSCF Potential source contribution function -- SNA Sulfate, nitrate and ammonium -- WSI Water-soluble ion; Pollution -- Periodicals; Pollution -- Environmental aspects -- Periodicals; Environmental Pollution -- Periodicals; Pollution -- Périodiques; Pollution -- Aspect de l'environnement -- Périodiques; Pollution -- Effets physiologiques -- Périodiques; Pollution; Pollution -- Environmental aspects; Periodicals; Electronic journals; 363.73
• DOI: 10.1016/j.envpol.2022.119951
• Languages: English
• ISSNs: 0269-7491

Abstract

Abstract: This study investigated the hourly inorganic aerosol chemistry and its impact on atmospheric visibility over an urban area in Central Taiwan, by relying on measurements of aerosol light extinction, inorganic gases, and PM2.5 water-soluble ions (WSIs), and simulations from a thermodynamic equilibrium model. On average, the sulfate (SO4 2− ), nitrate (NO3 − ), and ammonium (NH4 + ) components (SNA) contributed ∼90% of WSI concentrations, which in turn made up about 50% of the PM2.5 mass. During the entire observation period, PM2.5 and SNA concentrations, aerosol pH, aerosol liquid water content (ALWC), and sulfur and nitrogen conversion ratios all increased with decreasing visibility. In particular, the NO3 − contribution to PM2.5 increased, whereas the SO4 2− contribution decreased, with decreasing visibility. The diurnal variations of the above parameters indicate that the interaction and likely mutual promotion between NO3 − and ALWC enhanced the hygroscopicity and aqueous-phase reactions conducive for NO3 − formation, thus led to severely impaired visibility. The high relative humidity (RH) at the study area (average 70.7%) was a necessary but not sole factor leading to enhanced NO3 − formation, which was more directly associated with elevated ALWC and aerosol pH. Simulations from the thermodynamic model depict that the inorganic aerosol system in the study area was characterized by fully neutralized SO4 2− (i.e. a saturated factor in visibility reduction) and excess NH4 + amidst a NH3 -rich environment. As a result, PM2.5 composition was most sensitive to gas-phase HNO3, and hence NOx, and relatively insensitive to NH3 . Consequently, a reduction of NOx would result in instantaneous cuts of NO3 −, PM2.5, and ALWC, and hence improved visibility. On the other hand, a substantial amount of NH3 reduction (>70%) would be required to lower the aerosol pH, driving more than 50% of the particulate phase NO3 − to the gas phase, thereby making NH3 a limiting factor in shifting PM2.5 composition. Graphical abstract: The limiting, abundant, promoting, and saturated factor in the inorganic aerosol system affecting atmospheric visibility. Image 1 Highlights: Acid/basic gases and PM2.5 water-soluble ions were measured hourly in urban air. Thermodynamic model was used to predict the inorganic aerosols at equilibrium. Only nitrate contribution to PM2.5 increased with decreasing visibility. Elevated nitrate, aerosol water and pH under stagnant air led to poor visibility. PM2.5 was sensitive to HNO3 and hence NOx, and relatively insensitive to NH3 .