Spatial and seasonal variability of PM&amp;lt;sub&amp;gt;2.5&amp;lt;/sub&amp;gt; acidity at two Chinese megacities: insights into the formation of secondary inorganic aerosols

He, Kebin; Zhao, Qingguo; Ma, Yue; Duan, Fengkui; Yang, Fumo; Shi, Zongbo; Chen, G.

doi:10.5194/acp-12-1377-2012

Cited by 169 publications

(113 citation statements)

References 76 publications

Supporting

Mentioning

101

Contrasting

Order By: Relevance

“…The average reverse mode pH reported by previous studies ranged from -1 to 6.2 (Cheng et al, 2011;He et al, 2012;Tian et al, 2018;Cheng et al, 2016). Our calculations show that the reverse mode pH has a bimodal distribution with peaks between -2 and 2 (highly acidic) and between 7 and 10 (basic), and is very sensitive to errors in ionic measurements (Sect.…”

Section: Summary Of Existing Studiesmentioning

confidence: 68%

Fine particle pH for Beijing winter haze as inferred from different thermodynamic equilibrium models

Song¹,

Gao²,

Xu³

et al. 2018

Preprint

View full text Add to dashboard Cite

Abstract. pH is an important property of aerosol particles but is difficult to measure directly. Several studies have estimated the pH values for fine particles in North China winter haze using thermodynamic models (i.e., E-AIM and ISORROPIA) and ambient measurements. The reported pH values differ widely, ranging from close to 0 (highly acidic) to as high as 7 (neutral).In order to understand the reason for this discrepancy, we calculated pH values using these models with different assumptions 25 with regard to model inputs and particle phase states. We find that the large discrepancy is due primarily to differences in the model assumptions adopted in previous studies. Calculations using only aerosol phase composition as inputs (i.e., reverse mode) are sensitive to the measurement errors of ionic species and inferred pH values exhibit a bimodal distribution with peaks between −2 and 2 and between 7 and 10. Calculations using total (gas plus aerosol phase) measurements as inputs (i.e., forward mode) are affected much less by the measurement errors, and results are thus superior to those obtained from the reverse mode 30 calculations. Forward mode calculations in this and previous studies collectively indicate a moderately acidic condition (pH from about 4 to about 5) for fine particles in North China winter haze, indicating further that ammonia plays an important role in determining this property. The differences in pH predicted by the forward mode E-AIM and ISORROPIA calculations may be attributed mainly to differences in estimates of activity coefficients for hydrogen ions. The phase state assumed, which can be either stable (solid plus liquid) or metastable (only liquid), does not significantly impact pH predictions of ISORROPIA. 35Atmos. Chem. Phys. Discuss., https://doi

show abstract

Section: Summary Of Existing Studiesmentioning

confidence: 68%

Fine particle pH for Beijing winter haze as inferred from different thermodynamic equilibrium models

Song¹,

Gao²,

Xu³

et al. 2018

Preprint

View full text Add to dashboard Cite

show abstract

“…However, the prevailing winds in the dust storm time prevented the boundary layer NO x from being transported onto the mountain free troposphere, thus NO − 3 formation was depressed, resulting in the alpine fine particles becoming less acidic when dust was present. Such an increased acidity of airborne particles was also observed in other Chinese mega-cities such as Shanghai , Beijing and Chongqing (He et al, 2012) in the presence of dust storm.…”

Section: Difference In Aerosol Acidity Between Xi'an Andmentioning

confidence: 72%

“…Ca(NO 3 ) 2 is hydrophilic and fine particulate Ca(NO 3 ) 2 can deliquescence above ∼ 10 % relative humidity (Tobo et al, 2010). During the dust storm period, the fast formed Ca(NO 3 ) 2 can form a liquid film on the dust surface, which further promotes formation of nitric acid on the liquid phase by hydrolysis of other nitrogen oxides like N 2 O 5 (He et al, 2012;Pathak et al, 2009) and adsorption of gaseous HNO 3 (Goodman et al, 2000). Such a positive feedback resulted in a significant formation of NO − 3 even in the dry condition of the dust storm period.…”

Section: Difference In Aerosol Acidity Between Xi'an Andmentioning

confidence: 99%

Impact of Gobi desert dust on aerosol chemistry of Xi'an, inland China during spring 2009: differences in composition and size distribution between the urban ground surface and the mountain atmosphere

et al. 2013

View full text Add to dashboard Cite

Abstract. Composition and size distribution of atmospheric aerosols from Xi'an city (∼ 400 m, altitude) in inland China during the spring of 2009 including a massive dust event on 24 April were measured and compared with a parallel measurement at the summit (2060 m, altitude) of Mt. Hua, an alpine site nearby Xi'an. EC (elemental carbon), OC (organic carbon) and major ions in the city were 2-22 times higher than those on the mountaintop during the whole sampling period. Compared to that in the non-dust period a sharp increase in OC was observed at both sites during the dust period, which was mainly caused by an input of biogenic organics from the Gobi desert. However, adsorption/heterogeneous reaction of gaseous organics with dust was another important source of OC in the urban, contributing 22 % of OC in the dust event. In contrast to the mountain atmosphere where fine particles were less acidic when dust was present, the urban fine particles became more acidic in the dust event than in the non-dust event, mainly due to enhanced heterogeneous formation of nitrate and diluted NH 3 . Cl − and NO − 3 in the urban air during the dust event significantly shifted toward coarse particles. Such redistributions were further pronounced on the mountaintop when dust was present, resulting in both ions almost entirely staying in coarse particles. On the contrary, no significant spatial difference in size distribution of SO 2− 4 was found between the urban ground surface and the mountain atmosphere, which dominated in the fine mode (< 2.1 µm) during the nonevent and comparably distributed in the fine (< 2.1 µm) and coarse (> 2.1 µm) modes during the dust event.

show abstract

“…Molar ratios that yield a charge balance (i.e., equivalence ratios of unity or greater) are assumed for fully neutralized aerosol, while decreasing cation / anion ratios are assumed to represent decreasing aerosol pH (He et al, 2012;Kerminen et al, 2001;Huang et al, 2013). The data and assumptions that underlie the molar ratio method are the same as those used to calculate the ion balance.…”

Section: Molar Ratio Vs Phmentioning

confidence: 99%

A critical evaluation of proxy methods used to estimate the acidity of atmospheric particles

et al. 2015

View full text Add to dashboard Cite

Abstract. Given significant challenges with available measurements of aerosol acidity, proxy methods are frequently used to estimate the acidity of atmospheric particles. In this study, four of the most common aerosol acidity proxies are evaluated and compared: (1) the ion balance method, (2) the molar ratio method, (3) thermodynamic equilibrium models, and (4) the phase partitioning of ammonia. All methods are evaluated against predictions of thermodynamic models and against direct observations of aerosol-gas equilibrium partitioning acquired in Mexico City during the Megacity Initiative: Local and Global Research Objectives (MILAGRO) study. The ion balance and molar ratio methods assume that any deficit in inorganic cations relative to anions is due to the presence of H + and that a higher H + loading and lower cation / anion ratio both correspond to increasingly acidic particles (i.e., lower pH). Based on the MILAGRO measurements, no correlation is observed between H + levels inferred with the ion balance and aerosol pH predicted by the thermodynamic models and NH 3 -NH + 4 partitioning. Similarly, no relationship is observed between the cation / anion molar ratio and predicted aerosol pH. Using only measured aerosol chemical composition as inputs without any constraint for the gas phase, the E-AIM (Extended Aerosol Inorganics Model) and ISORROPIA-II thermodynamic equilibrium models tend to predict aerosol pH levels that are inconsistent with the observed NH 3 -NH + 4 partitioning. The modeled pH values from both E-AIM and ISORROPIA-II run with gas + aerosol inputs agreed well with the aerosol pH predicted by the phase partitioning of ammonia. It appears that (1) thermodynamic models constrained by gas + aerosol measurements and (2) the phase partitioning of ammonia provide the best available predictions of aerosol pH. Furthermore, neither the ion balance nor the molar ratio can be used as surrogates for aerosol pH, and previously published studies with conclusions based on such acidity proxies may need to be reevaluated. Given the significance of acidity for chemical processes in the atmosphere, the implications of this study are important and far reaching.

show abstract

Spatial and seasonal variability of PM<sub>2.5</sub> acidity at two Chinese megacities: insights into the formation of secondary inorganic aerosols

Cited by 169 publications

References 76 publications

Fine particle pH for Beijing winter haze as inferred from different thermodynamic equilibrium models

Fine particle pH for Beijing winter haze as inferred from different thermodynamic equilibrium models

Impact of Gobi desert dust on aerosol chemistry of Xi'an, inland China during spring 2009: differences in composition and size distribution between the urban ground surface and the mountain atmosphere

A critical evaluation of proxy methods used to estimate the acidity of atmospheric particles

Contact Info

Product

Resources

About