Ice nucleating particles (INPs) are vital for ice initiation in, and precipitation from, mixed-phase clouds. A source of INPs from oceans within sea spray aerosol (SSA) emissions has been suggested in previous studies but remained unconfirmed. Here, we show that INPs are emitted using real wave breaking in a laboratory flume to produce SSA. The number concentrations of INPs from laboratorygenerated SSA, when normalized to typical total aerosol number concentrations in the marine boundary layer, agree well with measurements from diverse regions over the oceans. Data in the present study are also in accord with previously published INP measurements made over remote ocean regions. INP number concentrations active within liquid water droplets increase exponentially in number with a decrease in temperature below 0°C, averaging an order of magnitude increase per 5°C interval. The plausibility of a strong increase in SSA INP emissions in association with phytoplankton blooms is also shown in laboratory simulations. Nevertheless, INP number concentrations, or active site densities approximated using "dry" geometric SSA surface areas, are a few orders of magnitude lower than corresponding concentrations or site densities in the surface boundary layer over continental regions. These findings have important implications for cloud radiative forcing and precipitation within low-level and midlevel marine clouds unaffected by continental INP sources, such as may occur over the Southern Ocean.marine aerosols | ice nucleation | clouds

Abstract. An airfreight container with automated

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Abstract. The removal of molecular hydrogen (H 2 ) from the atmosphere is dominated by the uptake in soils. Notwithstanding, estimates of the magnitude of this important process on a global scale are highly uncertain. The CARIBIC aircraft observations of the seasonal variations of H 2 and its D/H isotopic ratio in the Northern Hemisphere allow an independent, better constrained estimate. We derive that 82% of the annual turnover of tropospheric H 2 is due to soil uptake, equaling 88 (±11) Tg a −1 , of which the Northern Hemisphere alone accounts for 62 (±10) Tg a −1 . Our calculations further show that tropospheric H 2 has a lifetime of only 1.4 (±0.2) years -significantly shorter than the recent estimate of ∼2 years -which is expected to decrease in the future. In addition, our independent top-down approach, confined by the global and hemispheric sinks of H 2 , indicates 64 (±12) Tg a −1 emissions from various sources of volatile organic compounds by photochemical oxidation in the atmosphere. This estimate is as much as up to 60% larger than the previous estimates. This large airborne production of H 2 helps to explain the fairly homogeneous distribution of H 2 in the troposphere.