Reactive iodine and bromine species (RIS and RBS, respectively) are known for altering atmospheric chemistry and causing sharp tropospheric ozone (O) depletion in polar regions and significant O reduction in the marine boundary layer (MBL). Here we use measurement-based modeling to show that, unexpectedly, both RIS and RBS can lead to enhanced O formation in a polluted marine environment under volatile organic compound (VOC)-limited conditions associated with high nitrogen oxide (NO = [NO] + [NO]) concentrations. Under these conditions, the daily average O mixing ratio increased to ∼44 and ∼28% for BrO and IO mixing ratios of up to ∼6.8 and 4.7 ppt, respectively. The increase in the level of O was partially induced by enhanced ClNO formation for higher Br and I emission flux. The increase in the level of O was associated with an increased mixing ratio of hydroperoxyl radical to hydroxyl radical ([HO]/[OH]) and increased [NO]/[NO] with higher levels of RBS and/or RIS. NO-rich conditions are typical of the polluted MBL, near coastlines and ship plumes. Considering that O is toxic to humans, plants, and animals and is a greenhouse gas, our findings call for adequate updating of local and regional air-quality models with the effects of activities of RBS and RIS on O mixing ratios in the polluted MBL.

Volatile halogenated organic compounds (VHOCs), such as methyl halides (CH 3 X; X is Br, Cl and I) and very short-lived halogenated substances (VSLSs; bromoform -CHBr 3 , dibromomethane -CH 2 Br 2 , bromodichloromethane -CHBrCl 2 , trichloroethylene -C 2 HCl 3 , chloroform -CHCl 3 -and dibromochloromethane -CHBr 2 Cl) are well known for their significant influence on ozone concentrations and oxidation capacity of the troposphere and stratosphere and for their key role in aerosol formation. Insufficient characterization of the sources and the emission rate of VHOCs limits our ability to understand and assess their impact in both the troposphere and stratosphere. Over the last two decades, several natural terrestrial sources for VHOCs, including soil and vegetation, have been identified, but our knowledge of emission rates from these sources and their responses to changes in ambient conditions remains limited. Here we report measurements of the mixing ratios and fluxes of several chlorinated and brominated VHOCs from different landscapes and natural and agricultural vegetated sites at the Dead Sea during different seasons. Fluxes were generally positive (emission into the atmosphere), corresponding to elevated mixing ratios, but were highly variable. Fluxes (and mixing ratios) for the investigated VHOCs ranged as follows: CHBr 3 from −79 to 187 nmol m −2 d −1 (1.9 to 22.6 pptv), CH 2 Br 2 from −55 to 71 nmol m −2 d −1 (0.7 to 19 pptv), CHBr 2 Cl from −408 to 768 nmol m −2 d −1 (0.4 to 11 pptv), CHBrCl 2 from −29 to 45 nmol m −2 d −1 (0.5 to 9.6 pptv), CHCl 3 from −577 to 883 nmol m −2 d −1 (15 to 57 pptv), C 2 HCl 3 from −74 to 884 nmol m −2 d −1 (0.4 to 11 pptv), methyl chloride (CH 3 Cl) from -5300 to 10,800 nmol m −2 d −1 (530 to 730 pptv), methyl bromide (CH 3 Br) from −111 to 118 nmol m −2 d −1 (7.5 to 14 pptv) and methyl iodide (CH 3 I) from −25 to 17 nmol m −2 d −1 (0.4 to 2.8 pptv). Taking into account statistical uncertainties, the coastal sites (particularly those where soil is mixed with salt deposits) were identified as sources of all VHOCs, but this was not statistically significant for CHCl 3 . Further away from the coastal area, the bare soil sites were sources for CHBrCl 2 , CHBr 2 Cl, CHCl 3 , and probably also for CH 2 Br 2 and CH 3 I, and the agricultural sites were sources for CHBr 3 , CHBr 2 Cl and CHBrCl 2 . In contrast to previous reports, we also observed emissions of brominated trihalomethanes, with net molar fluxes ordered as follows: CHBr 2 Cl > CHCl 3 > CHBr 3 > CHBrCl 2 and lowest positive flux incidence for CHCl 3 among all trihalomethanes; this finding can be explained by the soil's enrichment with Br. Correlation analysis, in agreement with recent studies, indicated common controls for the emission of CHBr 2 Cl and CHBrCl 2 and likely also for CHBr 3 . There were no indications for correlation of the brominated trihalomethanes with CHCl 3 . Also in line with previous reports, we observed elevated emissions of Published by Copernicus Publications on behalf of the European Geosciences ...

Streaming algorithms are algorithms for processing large data streams, using only a limited amount of memory. Classical streaming algorithms operate under the assumption that the input stream is fixed in advance. Recently, there is a growing interest in studying streaming algorithms that provide provable guarantees even when the input stream is chosen by an adaptive adversary. Such streaming algorithms are said to be adversarially-robust. We propose a novel framework for adversarial streaming that hybrids two recently suggested frameworks by Hassidim et al. (2020) and by Woodruff and Zhou (2021). These recently suggested frameworks rely on very different ideas, each with its own strengths and weaknesses. We combine these two frameworks (in a nontrivial way) into a single hybrid framework that gains from both approaches to obtain superior performances for turnstile streams.

<p><strong>Abstract.</strong> Volatile halogenated organic compounds (VHOCs), such as methyl halides (CH<sub>3</sub>X; X = Br, Cl and I) and very short-lived halogenated substances (VSLS; CHBr<sub>3</sub>, CH<sub>2</sub>Br<sub>2</sub>, CHBrCl<sub>2</sub>, C<sub>2</sub>HCl<sub>3</sub>, CHCl<sub>3</sub> and CHBr<sub>2</sub>Cl) are well known for their significant influence on ozone concentrations and oxidation capacity of the troposphere and stratosphere, and for their key role in aerosol formation. Insufficient characterization of the sources and emission rate of VHOCs limits our present ability to understand and assess their impact in both the troposphere and the stratosphere. Over the last two decades several natural terrestrial sources for VHOCs, including soil and vegetation, have been identified, but our knowledge about emission rates from these sources and their responses to changes in ambient conditions remains limited. Here we report measurements of the mixing ratios and the fluxes of several chlorinated and brominated VHOCs from different landforms and vegetated sites at the Dead Sea during different seasons. Fluxes were highly variable but were generally positive (emissive), corresponding with elevated mixing ratios for all of the VHOCs investigated in the four investigated site types – bare soil, coastal, cultivated and natural vegetated sites – except for fluxes of CH<sub>3</sub>I and C<sub>2</sub>HCl<sub>3</sub> over the vegetated sites. In contrast to previous reports, we also observed emissions of brominated trihalomethanes, with net molar fluxes ordered as follows: CHBr<sub>2</sub>Cl > CHBr<sub>3</sub> > CHBrCl<sub>2</sub> > CHCl<sub>3</sub>. This finding can be explained by the enrichment of soil with Br. Correlation analysis, in agreement with recent studies, indicated common controls for the formation and emission of all the above trihalomethanes but also for CH<sub>2</sub>Br<sub>2</sub>. Also in line with previous reports, we observed elevated emissions of CHCl<sub>3</sub> and C<sub>2</sub>HCl<sub>3</sub> from mixtures of soil and different salt-deposited structures; the high correlations of flux with methyl halides, and particularly with CH<sub>3</sub>I, suggested that at least CH<sub>3</sub>I is also emitted via similar mechanisms or is subjected to similar controls. Overall, our results indicate elevate emission of VHOCs from bare soil under semi-arid conditions. Along with other recent studies, our findings point to the strong emission potential of a suite of VHOCs from saline soils and salt lakes, and call for additional studies of emission rates and mechanisms of VHOCs from saline soils and salt lakes.</p>

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CountSketch is a popular dimensionality reduction technique that maps vectors to a lower dimension using randomized linear measurements. The sketch supports recovering 2 -heavy hitters of a vector (entries withWe study the robustness of the sketch in adaptive settings where input vectors may depend on the output from prior inputs. Adaptive settings arise in processes with feedback or with adversarial attacks. We show that the classic estimator is not robust, and can be attacked with a number of queries of the order of the sketch size. We propose a robust estimator (for a slightly modified sketch) that allows for quadratic number of queries in the sketch size, which is an improvement factor of √ k (for k heavy hitters) over prior work.

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