Speciation of the major inorganic salts in atmospheric aerosols of Beijing, China: Measurements and comparison with model

Abstract

h i g h l i g h t sNH 4 NO 3 , NH 4 Cl and (NH 4 ) 2 SO 4 were measured in Beijing atmosphere. Sulfate, nitrate and chloride associated with crustal ions were important. ISORROPIA II was used to investigate the gas-aerosol equilibrium characteristics. Crustal species should be carefully considered to improve model prediction. In the winter and summer of 2013e2014, we used a sampling system, which consists of annular denuder, back-up filter and thermal desorption set-up, to measure the speciation of major inorganic salts in aerosols and the associated trace gases in Beijing. This sampling system can separate volatile ammonium salts (NH 4 NO 3 and NH 4 Cl) from non-volatile ammonium salts ((NH 4 ) 2 SO 4 ), as well as the non-volatile nitrate and chloride. The measurement data was used as input of a thermodynamic equilibrium model (ISORROPIA II) to investigate the gaseaerosol equilibrium characteristics. Results show that (NH 4 ) 2 SO 4 , NH 4 NO 3 and NH 4 Cl were the major inorganic salts in aerosols and mainly existed in the fine particles. The sulfate, nitrate and chloride associated with crustal ions were also important in Beijing where mineral dust concentrations were high. About 19% of sulfate in winter and 11% of sulfate in summer were associated with crustal ions and originated from heterogeneous reactions or direct emissions. The nonvolatile nitrate contributed about 33% and 15% of nitrate in winter and summer, respectively. Theoretical thermodynamic equilibrium calculations for NH 4 NO 3 and NH 4 Cl suggest that the gaseous precursors were sufficient to form stable volatile ammonium salts in winter, whereas the internal mixing with sulfate and crustal species were important for the formation of volatile ammonium salts in summer. The results of the thermodynamic equilibrium model reasonably agreed with the measurements of aerosols and gases, but large discrepancy existed in predicting the speciation of inorganic ammonium salts. This indicates that the assumption on crustal species in the model was important for obtaining better understanding on gaseaerosol partitioning and improving the model prediction. a r t i c l e i n f o

Particulate pollutants in the Brazilian city of São Paulo: 1-year investigation for the chemical composition and source apportionment

“…This pattern has already been observed; in warmer ambient conditions the fine NO − 3 aerosols can be volatilized, increasing the ratio between these species (Rastogi and Sarin, 2009;Souza et al, 2014a). NH 4 NO 3 exists in a reversible equilibrium between HNO 3 and NH 3 (Tang et al, 2016). Ammonium concentrations were not significantly different (p ∼ 0.3) and were slightly higher in Int 2.5 (1712 ng m −3 ) than in Ext 2.5 (1370 ng m −3 ).…”

“…The formation of (NH 4 ) 2 SO 4 , a nonvolatile species, could represent a gas-to-particle conversion process and can account for the formation of new particles through nucleation (Mkoma et al, 2014;da Rocha et al, 2005) and can lead to CCN formation. NH 4 NO 3 and NH 4 Cl also have an important influence on Earth's acid deposition (Tang et al, 2016). Na + was strongly correlated with Cl − in Ext 2.5 (R = 0.78) and presented a relatively moderate correlation (R = 0.35) in Ext 2.5−10 .…”

“…Water-soluble ions (WSIs) account for another major fraction of aerosols in urban areas and are able to affect visibility, particle hygroscopicity and cloud formation; they also influence acidity in rainwater and impact climate (Cheng et al, 2011;Jung et al, 2009;Khoder and Hassan, 2008;Tan et al, 2009;Tang et al, 2016;Yang et al, 2015).…”

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

“…Yao et al (2002) pointed out an SOR lower than 0.10 under conditions of primary source emissions and higher than 0.10 when sulfate was mainly produced through the secondary transformation of SO 2 oxidation. The value of SOR reached 0.70 in August 2013, which may be due to the enhanced atmospheric oxidant levels, sufficient ammonia for neutralisation, and higher RH in summer at Gucheng (Tang et al, 2016).…”

Water-soluble organic carbon (WSOC) and its temperature-resolved carbon fractions in atmospheric aerosols in Beijing

“…Water-soluble inorganic ions were analyzed using similar methods in our previous studies (Lun et al, 2003;Tang et al, 2016). Water extracts of Teflon filters were analyzed for anions (SO 4 2 − , NO 3 − , Cl − ) and cations (Na + , Mg 2+ , K + ,…”