Yujiao Zhu

Concentration, Size Distribution, and Formation of Trimethylaminium and Dimethylaminium Ions in Atmospheric Particles over Marginal Seas of China*

AbstractIn this paper, the concentration, the size distribution, and the formation of dimethylaminium (DMA+) and trimethylaminium (TMA+) ions in atmospheric particles were studied during a cruise campaign over the Yellow Sea and the Bohai Sea of China in May 2012. The concentrations of DMA+ and TMA+ in particles smaller than 11 µm were 4.4 ± 3.7 and 7.2 ± 7.1 nmol m−3, respectively. The two ions had a good correlation (R2 = 0.86), and both had a moderately good correlation with chlorophyll a fluorescence (R2 = 0.66–0.67). The observed concentrations were from one to three orders of magnitude larger than the concentrations reported in other marine atmospheres. They were also much larger than the values observed at a coastal site neighboring the Yellow Sea in May–June 2013. The high concentrations of DMA+ and TMA+ observed in the marine atmosphere were probably associated with local biogenic activity instead of the long-range transport of these species from adjacent continents. The calculated mole ratios of...

Roles of SO2 oxidation in new particle formation events

The oxidation of SO2 is commonly regarded as a major driver for new particle formation (NPF) in the atmosphere. In this study, we explored the connection between measured mixing ratio of SO2 and observed long-term (duration>3 hr) and short-term (duration<1.5 hr) NPF events at a semi-urban site in Toronto. Apparent NPF rates (J30) showed a moderate correlation with the concentration of sulfuric acid ([H2SO4]) calculated from the measured mixing ratio of SO2 in long-term NPF events and some short-term NPF events (Category I) (R2=0.66). The exponent in the fitting line of J30~[H2SO4]n in these events was 1.6. It was also found that SO2 mixing ratios varied a lot during long-term NPF events, leading to a significant variation of new particle counts. In the SO2-unexplained short-term NPF events (Category II), analysis showed that new particles were formed aloft and then mixed down to the ground level. Further calculation results showed that sulfuric acid oxidized from SO2 probably made a negligible contribution to the growth of >10 nm new particles.

Insight into Generation and Evolution of Sea-Salt Aerosols from Field Measurements in Diversified Marine and Coastal Atmospheres

This report focuses on studying generation and/or evolution of sea-salt aerosols (SSA) on basis of measurements in the Northwest Pacific Ocean (NWPO), the marginal seas of China, at sea-beach sites and a semi-urban coastal site in 2012–2015. From measurements in the NWPO, we obtained the smallest generation function of the super-micron SSA mass ([MSSA]) by the local wind comparing to those previously reported. Vessel-caused wave-breaking was found to greatly enhance generation of SSA and increase [MSSA], which was subject to non-natural generation of SSA. However, naturally enhanced generation of SSA was indeed observed in the marginal seas and at the sea-beach site. The two enhancement mechanisms may explain the difference among this and previous studies. Size distributions of super-micron SSA exhibited two modes, i.e., 1–2 μm mode and ~5 μm mode. The 1–2 μm mode of SSA was enhanced more and comparable to the ~5 μm mode under the wind speed >7 m/s. However, the smaller mode SSA was largely reduced from open oceans to sea-beach sites with reducing wind speed. The two super-micron modes were comparable again at a semi-urban coastal site, suggesting that the smaller super-micron mode SSA may play more important roles in atmospheres.

Concentration and size distribution of water-extracted dimethylaminium and trimethylaminium in atmospheric particles during nine campaigns - Implications for sources, phase states and formation pathways

In this study, we determined the concentrations of water-extracted dimethylaminium (DMA+) and trimethylaminium (TMA+) in size-segregated atmospheric particles collected during three inland campaigns and one sea-beach campaign in Qingdao and five marine campaigns in marginal seas of China and the northwest Pacific Ocean. The averages of DMA+ and TMA+ in PM0.056-10 (the sum of concentrations from 0.056 to 10μm) during each campaign ranged from 0.045 to 1.1nmolm-3 and from 0.029 to 0.53nmolm-3, respectively. The increased concentrations of DMA+ and TMA+ in PM0.056-10, particularly the 1-2 orders of magnitude increased ratios of DMA+/NH4+ and TMA+/NH4+, in the marine and sea-beach atmospheres indicated that the overwhelming majority was derived from marine sources. Size distributions of TMA+ and DMA+ were also investigated in terms of phase states and formation pathways, e.g., the dominant modes of particulate DMA+ and TMA+ in some samples were characterized by the mass median aerodynamic diameter at 0.1-0.2μm against the dominant mode of NH4+ and SO42- at 0.7-0.9μm, while the ratios of DMA+/NH4+ and/or TMA+/NH4+ in <0.2μm particles increased by 3-10 times from the corresponding lower values in >0.2μm particles. This strongly implied that the particulate DMA+ and TMA+ at <0.2μm size range overwhelmingly existed in the liquid organic phase as unprotonated TMA and DMA, but those at the >0.2μm size range mainly existed in the aqueous (or solid) phase where the dominance of gas-aerosol equilibria would cause the ratios to be almost size-independent. The size-dependent phase states corresponded to their various formation pathways.