Electrochemical ozone sensors : A miniaturised alternative for ozone measurements in laboratory experiments and air-quality monitoring

Ozone (O3) measurements are a critical component of air quality management and many atmospheric chemistry laboratory experiments. Conventional ozone monitoring devices based on UV absorption are relatively cumbersome and expensive, and have a relative high power consumption that limits their use to fixed sites. In this study electrochemical O3 sensors (OXB421, Alphasense) were used in a miniaturised O3 measurement device combined with LabJack and Labview data acquisition (DAQ). The device required a power supply of 5 V direct current (VDC) with a total power consumption of approximately 5 W. Total weight was less than 0.5 kg, low enough for portable in situ field deployment. The electrochemical O3 sensors produced a voltage signal positively proportional to O3 concentrations over the range of 5 ppb–10 ppm. There was excellent agreement between the performances of two O3 sensors with a good linear coefficient (R2 = 0.9995). The influences of relative humidity (RH) and gas sample flow rate on sensor calibrations and sensitivities have been investigated separately. Coincident calibration curves indicate that sensor performances were almost identical even at different RHs and flow rates after a re-zeroing process to offset the sensor baseline drifts. Rapid RH changes (∼20%/min) generate significant and instant changes in sensor signal, and the sensors consistently take up to 40 min to recover their original values after such a rapid RH change. In contrast, slow RH changes (∼0.1%/min) had little effect on sensor response. To test the performance of the miniaturised O3 device for real-world applications, the O3 sensors were employed for (i) laboratory experiments to measure O3 loss by seawater uptake and (ii) air quality monitoring over an 18-day period. It was found that ozone uptake by seawater was linear to the volume of linoleic acid on a sea surface microlayer and the calculated uptake coefficients based on sensor measurements were close to those from previous studies. For the 18-day period of air quality monitoring the corrected data from the O3 sensor was in a good agreement with those obtained by reference UV O3 analyser with an r2 of 0.83 (n = 8502). The novelty of this study is that the electrochemical O3 sensor was comprehensively investigated in O3 measurements in both laboratory and ambient air quality monitoring and it can to be a miniaturised alternative for conventional O3 monitoring devices due to its low cost, low power-consumption, portable and simple-conduction properties

Halocarbons associated with Arctic sea ice

Short-lived halocarbons were measured in Arctic sea-ice brine, seawater and air above the Greenland and Norwegian seas (∼81°N, 2 to 5°E) in mid-summer, from a melting ice floe at the edge of the ice pack. In the ice floe, concentrations of C2H5I, 2-C3H7I and CH2Br2 showed significant enhancement in the sea ice brine, of average factors of 1.7, 1.4 and 2.5 times respectively, compared to the water underneath and after normalising to brine volume. Concentrations of mono-iodocarbons in air are the highest ever reported, and our calculations suggest increased fluxes of halocarbons to the atmosphere may result from their sea-ice enhancement. Some halocarbons were also measured in ice of the sub-Arctic in Hudson Bay (∼55°N, 77°W) in early spring, ice that was thicker, colder and less porous than the Arctic ice in summer, and in which the halocarbons were concentrated to values over 10 times larger than in the Arctic ice when normalised to brine volume. Concentrations in the Arctic ice were similar to those in Antarctic sea ice that was similarly warm and porous. As climate warms and Arctic sea ice becomes more like that of the Antarctic, our results lead us to expect the production of iodocarbons and so of reactive iodine gases to increase

Halogens in seaweeds : Biological and Environmental Significance

Acknowledgments: We are grateful to the Kuwait Institute for Scientific Research (KISR) for PhD 1129 funding for Hanan Al-Adilah and to the European Commission for a Marie Curie International In- 1130 coming Fellowship (Horizon 2020 Research and Innovation Programme of the European Union un- 1131 der the Marie Skłodowska-Curie grant agreement No 839151) to Puja Kumari. We would equally 1132 like to thank the UK Natural Environment Research Council for their support to FCK (program 1133 Oceans 2025 – WP 4.5 and grants NE/D521522/1 and NE/J023094/1) and LJC (grant NE/N009983/1). 1134 This work also received support from the Marine Alliance for Science and Technology for Scotland 1135 pooling initiative. MASTS is funded by the Scottish Funding Council (grant reference HR09011) and 1136 contributing institutions. MCF, FCK and HAA thank the Lorentz Center (funded by the Netherlands 1137 Organization for Scientific Research, NWO, and the University of Leiden) for the organization of 1138 the workshop ‘IODINE: Biogeochemical Cycle of Iodine and Human Health’ (Oct. 4-6, 2017) which 1139 partly inspired this review. LJC acknowledges funding from the European Research Council (ERC) 1140 under the European Union’s Horizon 2020 programme (project O3-SML; grant agreement no. 1141 833290).Peer reviewedPublisher PD

Evidence for renoxification in the tropical marine boundary layer

We present 2 years of NOx observations from the Cape Verde Atmospheric Observatory located in the tropical Atlantic boundary layer. We find that NOx mixing ratios peak around solar noon (at 20-30pptV depending on season), which is counter to box model simulations that show a midday minimum due to OH conversion of NO2 to HNO3. Production of NOx via decomposition of organic nitrogen species and the photolysis of HNO3 appear insufficient to provide the observed noontime maximum. A rapid photolysis of nitrate aerosol to produce HONO and NO2, however, is able to simulate the observed diurnal cycle. This would make it the dominant source of NOx at this remote marine boundary layer site, overturning the previous paradigm according to which the transport of organic nitrogen species, such as PAN, is the dominant source. We show that observed mixing ratios (November-December 2015) of HONO at Cape Verde (∼ 3.5pptV peak at solar noon) are consistent with this route for NOx production. Reactions between the nitrate radical and halogen hydroxides which have been postulated in the literature appear to improve the box model simulation of NOx. This rapid conversion of aerosol phase nitrate to NOx changes our perspective of the NOx cycling chemistry in the tropical marine boundary layer, suggesting a more chemically complex environment than previously thought

HONO Measurement by Differential Photolysis

Nitrous acid (HONO) has been quantitatively measured in situ by differential photolysis at 385 and 395 nm, and subsequent detection as nitric oxide (NO) by the chemiluminescence reaction with ozone (O3). The technique has been evaluated by Fourier transform infrared (FT-IR) spectroscopy to provide a direct HONO measurement in a simulation chamber and compared side by side with a long absorption path optical photometer (LOPAP) in the field. The NO-O3 chemiluminescence technique is robust, well characterized, and capable of sampling at low pressure, whilst solid-state converter technology allows for unattended in situ HONO measurements in combination with fast time resolution and response

Observations of ozone-poor air in the tropical tropopause layer

Ozonesondes reaching the tropical tropopause layer (TTL) over the west Pacific have occasionally measured layers of very low ozone concentrations - less than 15 ppbv - raising the question of how prevalent such layers are and how they are formed. In this paper, we examine aircraft measurements from the Airborne Tropical Tropopause Experiment (ATTREX), the Coordinated Airborne Studies in the Tropics (CAST) and the Convective Transport of Active Species in the Tropics (CONTRAST) experiment campaigns based in Guam in January-March 2014 for evidence of very low ozone concentrations and their relation to deep convection. The study builds on results from the ozonesonde campaign conducted from Manus Island, Papua New Guinea, as part of CAST, where ozone concentrations as low as 12 ppbv were observed between 100 and 150 hPa downwind of a deep convective complex. TTL measurements from the Global Hawk unmanned aircraft show a marked contrast between the hemispheres, with mean ozone concentrations in profiles in the Southern Hemisphere between 100 and 150 hPa of between 10.7 and 15.2 ppbv. By contrast, the mean ozone concentrations in profiles in the Northern Hemisphere were always above 15.4 ppbv and normally above 20 ppbv at these altitudes. The CAST and CONTRAST aircraft sampled the atmosphere between the surface and 120 hPa, finding very low ozone concentrations only between the surface and 700 hPa; mixing ratios as low as 7 ppbv were regularly measured in the boundary layer, whereas in the free troposphere above 200 hPa concentrations were generally well in excess of 15 ppbv. These results are consistent with uplift of almost-unmixed boundary-layer air to the TTL in deep convection. An interhemispheric difference was found in the TTL ozone concentrations, with values < 15 ppbv measured extensively in the Southern Hemisphere but seldom in the Northern Hemisphere. This is consistent with a similar contrast in the low-level ozone between the two hemispheres found by previous measurement campaigns. Further evidence of a boundary-layer origin for the uplifted air is provided by the anticorrelation between ozone and halogenated hydrocarbons of marine origin observed by the three aircraft

Transport of short-lived halocarbons to the stratosphere over the Pacific Ocean

The effectiveness of transport of short-lived halocarbons to the upper troposphere and lower stratosphere remains an important uncertainty in quantifying the supply of ozone-depleting substances to the stratosphere. In early 2014, a major field campaign in Guam in the western Pacific, involving UK and US research aircraft, sampled the tropical troposphere and lower stratosphere. The resulting measurements of CH3I, CHBr3 and CH2Br2 are compared here with calculations from a Lagrangian model. This methodology benefits from an updated convection scheme that improves simulation of the effect of deep convective motions on particle distribution within the tropical troposphere. We find that the observed CH3I, CHBr3 and CH2Br2 mixing ratios in the tropical tropopause layer (TTL) are consistent with those in the boundary layer when the new convection scheme is used to account for convective transport. More specifically, comparisons between modelled estimates and observations of short-lived CH3I indicate that the updated convection scheme is realistic up to the lower TTL but is less good at reproducing the small number of extreme convective events in the upper TTL. This study consolidates our understanding of the transport of short-lived halocarbons to the upper troposphere and lower stratosphere by using improved model calculations to confirm consistency between observations in the boundary layer, observations in the TTL and atmospheric transport processes. Our results support recent estimates of the contribution of short-lived bromocarbons to the stratospheric bromine budget

Understanding Iodine Chemistry Over the Northern and Equatorial Indian Ocean

Observations of halogen oxides, ozone, meteorological parameters, and physical and biogeochemical water column measurements were made in the Indian Ocean and its marine boundary layer as a part of the Second International Indian Ocean Expedition (IIOE-2). The expedition took place on board the oceanographic research vessel Sagar Nidhi during 4–22 December 2015 from Goa, India, to Port Louis, Mauritius. Observations of mixed layer depth, averaged temperature, salinity, and nitrate concentrations were used to calculate predicted iodide concentrations in the seawater. The inorganic iodine ocean-atmosphere flux (hypoiodous acid [HOI] and molecular iodine [I2]) was computed using the predicted iodide concentrations, measured atmospheric ozone, and wind speed. Iodine oxide (IO) mixing ratios peaked at 0.47 ± 0.29 pptv (parts per trillion by volume) in the remote open ocean environment. The estimated iodide concentrations and HOI and I2 fluxes peaked at 200/500 nM, 410/680 nmol·m−2·day−1, and 20/80 nmol·m−2·day−1, respectively, depending on the parameterization used. The calculated fluxes for HOI and I2 were higher closer to the Indian subcontinent; however, atmospheric IO was only observed above the detection limit in the remote open ocean environment. We use NO2 observations to show that titration of IO by NO2 is the main reason for this result. These observations show that inorganic iodine fluxes and atmospheric IO show similar trends in the Indian Ocean marine boundary layer, but the impact of inorganic iodine emissions on iodine chemistry is buffered in elevated NOx environments, even though the estimated oceanic iodine fluxes are higher

Sarin Exposures in A Cohort of British Military Participants in Human Experimental Research at Porton Down 1945-1987

Background The effects of exposure to chemical warfare agents in humans are topical. Porton Down is the UK’s centre for research on chemical warfare where, since WWI, a programme of experiments involving ~30000 participants drawn from the UK armed services has been undertaken. Objectives Our aim is to report on exposures to nerve agents, particularly sarin, using detailed exposure data not explored in a previous analysis. Methods In this paper, we have used existing data on exposures to servicemen who attended the human volunteer programme at Porton Down to examine exposures to nerve agents in general and to sarin in particular. Results Six principal nerve agents were tested on humans between 1945 and 1987. Of all 4299 nerve agent tests recorded, 3511 (82%) were with sarin, most commonly in an exposure chamber, with inhalation being the commonest exposure route (85%). Biological response to sarin exposure was expressed as percentage change in cholinesterase activity and, less commonly, change in pupil size. For red blood cell cholinesterase, median inhibition for inhalation tests was 41% (interquartile range 28–51%), with a maximum of 87%. For dermal exposures the maximum inhibition recorded was 99%. There was a clear association between increasing exposure to sarin and depression of cholinesterase activity but the strength and direction of the association varied by exposure route and the presence of chemical or physical protection. Pupil size decreased with increased exposure but this relationship was less clear when modifiers, such as atropine drops, were present. Conclusions These results, drawn from high quality experimental data, offer a unique insight into the effects of these chemical agents on humans