Aerosol hygroscopicity and its link to chemical composition in the coastal atmosphere of Mace Head: marine and continental air masses

Abstract

Abstract. Chemical composition and hygroscopicity closure of marine aerosol in high time resolution has not been achieved yet due to the difficulty involved in measuring the refractory sea-salt concentration in near-real time. In this study, attempts were made to achieve closure for marine aerosol based on a humidified tandem differential mobility analyser (HTDMA) and a high-resolution time-of-flight aerosol mass spectrometer (AMS) for wintertime aerosol at Mace Head, Ireland. The aerosol hygroscopicity was examined as a growth factor (GF) at 90 % relative humidity (RH). The corresponding GFs of 35, 50, 75, 110 and 165 nm particles were 1.54±0.26, 1.60±0.29, 1.66±0.31, 1.72±0.29 and 1.78±0.30 (mean ± standard deviation), respectively. Two contrasting air masses (continental and marine) were selected to study the temporal variation in hygroscopicity; the results demonstrated a clear diurnal pattern in continental air masses, whereas no diurnal pattern was found in marine air masses. In addition, wintertime aerosol was observed to be largely externally mixed in both of the contrasting air masses. Concurrent high time resolution PM1 (particulate matter <1 µm) chemical composition data from combined AMS and MAAP measurements, comprising organic matter, non-sea-salt sulfate, nitrate, ammonium, sea salt and black carbon (BC), were used to predict aerosol hygroscopicity with the Zdanovskii–Stokes–Robinson (ZSR) mixing rule. Overall, good agreement (an R2 value of 0.824 and a slope of 1.02) was found between the growth factor of 165 nm particles measured by the HTDMA (GF_HTDMA) and the growth factor derived from the AMS + MAAP bulk chemical composition (GF_AMS). Over 95 % of the estimated GF values exhibited less than a 10 % deviation for the whole dataset, and this deviation was mostly attributed to the neglected mixing state as a result of the bulk PM1 composition.

The impact of aerosol size-dependent hygroscopicity and mixing state on the cloud condensation nuclei potential over the Northeast Atlantic

“…In Clean-H, the smaller particles exhibited higher hygroscopicity, while in Clean-L, it was the larger particles that were more hygroscopic. This pattern is attributed to the presence of Aitken mode near-hydrophobic particle in Clean-L, as highlighted in the previous study (Xu et al, 2020). The AR of less than 100% in Clean-L suggested that treating winter time marine aerosol as pure sea-salt or their mixture with nss-SO4 will likely induce an over-estimation of NCCN at higher SS.…”

“…S5), while the Aitken mode aerosol consisted of a fraction of near-hydrophobic particles (Fig. S5), which was not discerned by the bulk chemical composition due to negligible mass (Xu et al, 2020). As shown in Fig.…”

“…An HTDMA (Liu et al, 1978;Rader and McMurry, 1986;Swietlicki et al, 2008;Tang et al, 2019a) was used to measure the GF-PDF. A detailed description of the HTDMA instrument operated at MHD can be found in previous studies (Bialek et al, 2012;Xu et al, 2020). Briefly, the HTDMA consists of two DMAs, a temperature triggered humidifier and a CPC.…”

“…The clean marine sector criteria were used following the previous studies where westerly air masses with BC concentration of less than 15 ng m -3 convincingly separated anthropogenic impacted air masses (O'Dowd et al, 2014). The polluted continental sector was defined according to wind direction alone (Xu et al, 2020).…”

Global modeling of heterogeneous hydroxymethanesulfonate chemistry

“…Fourth, HMS, CH 3 SO 3 − , and Ca 2+ and Mg 2+ in fine dust are included in the ISORROPIA calculations. We assume the same hygroscopicity of HMS and MSA as sulfate (Xu et al, 2020).…”