|Silva, Philip - Phil|
Submitted to: Atmospheric Chemistry and Physics
Publication Type: Peer reviewed journal
Publication Acceptance Date: 4/10/2014
Publication Date: 6/17/2014
Citation: Tang, X., Price, D.J., Praske, E., Vu, D., Purvis-Roberts, K., Silva, P.J., Cocker, D.R., Asa-Awuku, A. 2014. Cloud condensation nuclei activity of aliphatic amine secondary aerosol. Atmospheric Chemistry and Physics. 14:5959–5967. Interpretive Summary: Gaseous amine emissions from waste handling can react to form aerosol particles and can impact cloud formation depending on how much the resulting particles absorb water in the atmosphere. In this paper, the potential of cloud forming activity of amine aerosols was studied for the first time using an environmental smog chamber under controlled laboratory conditions. Aerosols formed from nighttime reactions of amines showed a larger CCN potential than typical daytime photochemical reactions. Information from this study will help scientists in the aerosol and clouds community to better understand and model the effects of emissions on cloud formation.
Technical Abstract: Aliphatic amines can form secondary aerosol via oxidation with atmospheric radicals (e.g. hydroxyl radical and nitrate radical). The resulting particle composition can contain both secondary organic aerosol (SOA) and inorganic salts. The fraction of organic to inorganic materials in the particulate phase influences aerosol hygroscopicity and cloud condensation nuclei (CCN) activity. SOA formed from trimethylamine (TMA) and butylamine (BA) reactions with hydroxyl radical (OH) is composed of organic material of low hygroscopicity (k = 0.25). Secondary aerosol formed from the tertiary aliphatic amine (TMA) with N2O5 (source of nitrate radical, NO3) contains less volatile compounds than the primary aliphatic amine (BA) aerosol. TMA + N2O5 form semi-volatile organics in low RH conditions that have single parameter hygroscopicity, ' ~0.20, indicative of slightly soluble organic material. As RH increases, several inorganic amine salts are formed as a result of acid-base reactions. At RH =22% the TMA + N2O5 aerosol composition is a mixture of organics and inorganics. The Zdanovskii, Stokes, and Robinson (ZSR) mixing rule can be applied to CCN activity measurements of humid TMA-N2O5 secondary aerosol. Higher CCN activity (k >0.3) was also observed for humid BA+N2O5 aerosols compared with dry aerosol (k ~0.2), as a result of the formation of inorganic salts such as NH4NO3 and BA•HNO3. Compared with TMA, BA+N2O5 reactions produce more volatile aerosols. The BA+N2O5 aerosol products under humid experiments were found to be very sensitive to the temperature the CCN activity measurements were made at. The CCN counter, when set above a 21°C temperature difference, completely evaporates BA+N2O5 aerosol formed at RH = 30%; k ranges from 0.4 to 0.7 dependent on the instrument supersaturation settings. The aerosol behaves non-ideally, hence ZSR rules are not applied to the CCN results from the primary aliphatic amine system. Overall, aliphatic amine aerosol systems single parameter hygroscopicity ranges from 0.2 < k <0.7. This work indicates that aerosols formed via nighttime reactions with amines are likely to produce hygroscopic aerosol whereas photochemical reactions with OH produce secondary organic aerosol of lower CCN activity. The contributions of semi-volatile secondary organic and inorganic material from aliphatic amines must be considered for accurate hygroscopicity and CCN predictions from aliphatic amine systems.