Abstract
Abstract. Aerosol mass spectrometers (AMSs) and Aerosol Chemical Speciation Monitors (ACSMs) commercialized by Aerodyne are widely used to measure the non-refractory species in submicron particles. With the standard vapourizer (SV) that is installed in all commercial instruments to date, the quantification of ambient aerosol mass concentration requires the use of the collection efficiency (CE) to correct for the loss of particles due to bounce. A new capture vapourizer (CV) has been designed to reduce the need for a bounce-related CE correction. Two high-resolution AMS instruments, one with a SV and one with a CV, were operated side by side in the laboratory. Four standard species, NH4NO3, NaNO3, (NH4)2SO4 and NH4Cl, which typically constitute the majority of the mass of ambient submicron inorganic species, are studied. The effect of vapourizer temperature (Tv ∼ 200–800 °C) on the detected fragments, CE and size distributions are investigated. A Tv of 500–550 °C for the CV is recommended. In the CV, CE was identical (around unity) for more volatile species (e.g. NH4NO3) and comparable to or higher than the SV for less-volatile species (e.g. (NH4)2SO4), demonstrating an improvement in CE for laboratory inorganic species in the CV. The detected relative intensities of fragments of NO3 and SO4 species observed with the CV are different from those observed with the SV, and are consistent with additional thermal decomposition arising from the increased residence time and multiple collisions. Increased residence times with the CV also lead to broader particle size distribution measurements than with the SV. A method for estimating whether pure species will be detected in AMS sizing mode is proposed. Production of CO2(g) from sampled nitrate on the vapourizer surface, which has been reported for the SV, is negligible for the CV for NH4NO3 and comparable to the SV for NaNO3. . We observe an extremely consistent fragmentation for ammonium compared to very large changes for the associated anions. Together with other evidence, this indicates that it is unlikely that a major fraction of inorganic species vapourizes as intact salts in the AMS.
Highlights
Submicron aerosols have major effects on climate and human health (Hallquist et al, 2009; Heal et al, 2012; IPCC, 2013; Fuzzi et al, 2015)
collection efficiency (CE) < 1 in the Aerosol mass spectrometers (AMSs) can be due to particle loss within the (1) aerodynamic lens (EL), depending on particle size, lens design and pressure (Jayne et al, 2000; Liu et al, 2007; Bahreini et al, 2008); (2) particle time-of-flight (PToF) chamber (ES) caused by non-spherical particles that result in broader particle beams with some particles not reaching the vapourizer (Huffman et al, 2005; Salcedo et al, 2007), or (3) particle bounce on the vapourizer (EB)
Pieber et al (2016) recently showed that inorganic salts can produce CO2(g) from material that is accumulated on the surface of the AMS in the standard vapourizer (SV), and we investigate whether this effect is observed for the capture vapourizer (CV)
Summary
Submicron aerosols have major effects on climate and human health (Hallquist et al, 2009; Heal et al, 2012; IPCC, 2013; Fuzzi et al, 2015). Comparisons between AMS and other co-located aerosol instruments in various field studies (Drewnick et al, 2003, 2004b; Allan et al, 2004a; Takegawa et al, 2009; Docherty et al, 2011; Middlebrook et al, 2012) or laboratory studies (Bahreini et al, 2005; Matthew et al, 2008; Docherty et al, 2012) have shown that, despite the typically strong correlation between AMS and other aerosol instrument measurements, a correction factor needs to be used for mass quantification in the AMS. Fragmentation and quantification of NH4NO3 as a function of particle beam position on the vapourizers is investigated. Pieber et al (2016) recently showed that inorganic salts can produce CO2(g) from material that is accumulated on the surface of the AMS in the SV, and we investigate whether this effect is observed for the CV
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