Organosulfates are key compounds driving the anthropogenic enhancement of ambient organic aerosol, however, total organosulfate quantification remains elusive due to their molecular diversity and the scarcity of authentic standards. Here, we present a solid-phase extraction method that isolates organosulfates from ambient aerosol samples and enables their identification and quantification using mass spectrometry and a charged aerosol detector, respectively. We investigate ambient aerosol samples from urban China and rural Germany and quantify ~130 and ~65 chromatographically resolved organosulfates, respectively, contributing less than ~2% to the total organic matter. We find a significantly larger organosulfate fraction appearing as a broad peak in the chromatograms from the charged aerosol detector. Confirming its origin from chromatographically non-resolved organosulfates, an all-ion fragmentation experiment reveals specific sulfate-related ions. Integrating this peak, we find the contribution of organosulfates to organic aerosol is 12-17% and ~21% in samples from urban China and rural Germany, respectively. These findings emphasise the potential of sulfur emission reduction for mitigating both sulfate-related and organic aerosol pollution.

Particle hygroscopicity plays a key role in determining the particle deposition in the human respiratory tract (HRT). In this study, the effects of hygroscopicity and mixing state on regional and total deposition doses on the basis of the particle number concentration for children, adults, and the elderly were quantified using the Multiple-Path Particle Dosimetry model, based on the size-resolved particle hygroscopicity measurements at HRT-like conditions (relative humidity = 98 %) performed in the North China Plain. The measured particle population with an external mixing state was dominated by hygroscopic particles (number fraction = (91.5 ± 5.7) %, mean ± standard deviation (SD); the same below). Particle hygroscopic growth in the HRT led to a reduction by around 24 % in the total doses of submicron particles for all age groups. Such a reduction was mainly caused by the growth of hygroscopic particles and was more pronounced in the pulmonary and tracheobronchial regions. Regardless of hygroscopicity, the elderly group of people had the highest total dose among three age groups, while children received the maximum total deposition rate. With 270 nm in diameter as the boundary, the total deposition doses of particles smaller than this diameter were overestimated, and those of larger particles were underestimated, assuming no particle hygroscopic growth in the HRT. From the perspective of the daily variation, the deposition rates of hygroscopic particles with an average of (2.88 ± 0.81) × 10⁹ particles h⁻¹ during the daytime were larger than those at night ((2.32 ± 0.24) × 10⁹ particles h⁻¹). On the contrary, hydrophobic particles interpreted as freshly emitted soot and primary organic aerosols exhibited higher deposition rates at nighttime ((3.39 ± 1.34) × 10⁸ particles h⁻¹) than those in the day ((2.58 ± 0.76) × 10⁸ particles h⁻¹). The traffic emissions during the rush hours enhanced the deposition rate of hydrophobic particles. This work provides a more explicit assessment of the impact of hygroscopicity and mixing state on the deposition pattern of submicron particles in the HRT.