Hasil untuk "Earthwork. Foundations"

W. Krochin, W. Krochin, A. Murk et al.

<p>The oxygen emission band at 60 GHz is a commonly used frequency band for atmospheric temperature sounding. The fine structure emission lines used to retrieve temperature in the stratosphere and mesosphere are affected by the Zeeman effect, which has a characteristic influence on the spectral shape of different polarization states. As a consequence of this effect, a <span class="inline-formula"><i>V</i></span>-Stokes component is generated, indicating symmetry breaking between right and left circular polarized radiation. In this study, we present the full-rank Stokes vector of the fine structure emission lines at 53.067 and 53.596 GHz, measured with a fully polarimetric radiometer. We discuss the advantages of the fully polarimetric approach compared to single-polarization observations for temperature sounding by comparing both simulations and observations. Our findings show that using circular polarization in the retrieval algorithm improves both the upper altitude limit and vertical resolution by several kilometers. Additionally, we introduce an operational calibration method and present calibrated spectra for the four components of the Stokes polarization vector. We also provide a continuous series of retrieved temperature profiles, demonstrating that the calibration is valid for continuous observations.</p>

M. N. Fiddler, V. Moschos, M. M. McRee et al.

<p>Africa is a critical source of biomass burning (BB) aerosols, and its importance is increasing. The African Combustion Aerosol Collaborative Intercomparison Analysis (ACACIA) Pilot Project set to optically characterize BB aerosol generated from sub-Saharan African fuels. We used a photoacoustic spectrometer as a reference instrument to determine the multiple-scattering correction factor <span class="inline-formula"><i>C</i>_<i>λ</i></span> for an AE33 aethalometer at three wavelengths, which produced weighted mean values of <span class="inline-formula"><i>C</i>₃₇₀=3.69</span>, <span class="inline-formula"><i>C</i>₄₇₀=5.65</span>, and <span class="inline-formula"><i>C</i>₅₂₀=6.39</span>. <span class="inline-formula"><i>C</i>_<i>λ</i></span> increased with wavelength and <span class="inline-formula"><i>C</i>₃₇₀</span> was statistically independent of the others, suggesting a single <span class="inline-formula"><i>C</i>_<i>λ</i></span> is insufficient, especially in BB scenarios. While a dependence of <span class="inline-formula"><i>C</i>_<i>λ</i></span> on burning state was not found, <span class="inline-formula"><i>C</i>_<i>λ</i></span> was shown to strongly relate to particle single scattering albedo (SSA, <span class="inline-formula"><i>ω</i>)</span>. When <span class="inline-formula"><i>C</i>_<i>λ</i></span> was plotted against SSA, values slowly rose at low SSA values, followed by a sharp rise around an SSA of <span class="inline-formula">∼</span> 0.9; indicating a larger correction needed for less absorbing aerosol. A number of functions operating on either SSA or <span class="inline-formula"><i>C</i>_<i>λ</i></span> were explored and the best function was <span class="inline-formula"><math xmlns="http://www.w3.org/1998/Math/MathML" id="M14" display="inline" overflow="scroll" dspmath="mathml"><mrow><mo>-</mo><msub><mi>C</mi><mi mathvariant="italic">λ</mi></msub><mo>/</mo><mo>(</mo><mn mathvariant="normal">1</mn><mo>-</mo><msub><mi>C</mi><mi mathvariant="italic">λ</mi></msub><mo>)</mo><mo>=</mo><mi>A</mi><mi mathvariant="italic">ω</mi><mo>+</mo><mi>B</mi></mrow></math><span><svg:svg xmlns:svg="http://www.w3.org/2000/svg" width="112pt" height="14pt" class="svg-formula" dspmath="mathimg" md5hash="816afa37feb768cfd6c442b0a557c5aa"><svg:image xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="amt-19-307-2026-ie00001.svg" width="112pt" height="14pt" src="amt-19-307-2026-ie00001.png"/></svg:svg></span></span>. This is an important parametrization of <span class="inline-formula"><i>C</i>_<i>λ</i></span> specifically geared towards BB aerosol from African fuels under different aging states, and is of particular importance for future field work in that continent. An Ångström matrix plot shows that African BB aerosol can have values more akin to dust, which demonstrates that these fuels are distinct in their wavelength dependence from more typical BB aerosol. Lastly, we examined the mass extinction and absorbance cross sections for BB aerosol generated for the same fuels with two different tube furnace setups. Not only is this combustion method flexible, it was found to be reproducible between labs.</p>

Ke You, Lieyun Ding, Cheng Zhou et al.

I. Krisch, N. P. Hindley, O. Reitebuch et al.

<p>Since its launch in 2018, the European Space Agency's Earth Explorer satellite Aeolus has provided global height resolved measurements of horizontal wind in the troposphere and lower stratosphere for the first time. Novel datasets such as these provide an unprecedented opportunity for the research of atmospheric dynamics and provide new insights into the dynamics of the upper troposphere and lower stratosphere (UTLS) region. Aeolus measures the wind component along its horizontal line-of-sight, but for the analysis and interpretation of atmospheric dynamics, zonal and/or meridional wind components are most useful. In this paper, we introduce and compare three different methods to derive zonal and meridional wind components from the Aeolus wind measurements. We find that the most promising method involves combining Aeolus measurements during ascending and descending orbits. Using this method, we derive global estimates of the zonal wind in the latitude range 79.7<span class="inline-formula">^∘</span> S to 84.5<span class="inline-formula">^∘</span> N with errors of less than 5 m s<span class="inline-formula">⁻¹</span> (at the 2<span class="inline-formula"><i>σ</i></span> level). Due to the orbit geometry of Aeolus, the estimation of meridional wind in the tropics and at midlatitudes is more challenging and the quality is less reliable. However, we find that it is possible to derive meridional winds poleward of 70<span class="inline-formula">^∘</span> latitude with absolute errors typically below 5 m s<span class="inline-formula">⁻¹</span> (at the 2<span class="inline-formula"><i>σ</i></span> level). This further demonstrates the value of Aeolus wind measurements for applications in weather and climate research, in addition to their important role in numerical weather prediction.</p>

D. S. Wang, C. P. Lee, J. E. Krechmer et al.

<p>Online characterization of aerosol composition at the near-molecular level is key to understanding chemical reaction mechanisms, kinetics, and sources under various atmospheric conditions. The recently developed extractive electrospray ionization time-of-flight mass spectrometer (EESI-TOF) is capable of detecting a wide range of organic oxidation products in the particle phase in real time with minimal fragmentation. Quantification can sometimes be hindered by a lack of available commercial standards for aerosol constituents, however. Good correlations between the EESI-TOF and other aerosol speciation techniques have been reported, though no attempts have yet been made to parameterize the EESI-TOF response factor for different chemical species. Here, we report the first parameterization of the EESI-TOF response factor for secondary organic aerosol (SOA) at the near-molecular level based on its elemental composition. SOA was formed by ozonolysis of monoterpene or OH oxidation of aromatics inside an oxidation flow reactor (OFR) using ammonium nitrate as seed particles. A Vocus proton-transfer reaction mass spectrometer (Vocus-PTR) and a high-resolution aerosol mass spectrometer (AMS) were used to determine the gas-phase molecular composition and the particle-phase bulk chemical composition, respectively. The EESI response factors towards bulk SOA coating and the inorganic seed particle core were constrained by intercomparison with the AMS. The highest bulk EESI response factor was observed for SOA produced from 1,3,5-trimethylbenzene, followed by those produced from <span class="inline-formula"><i>d</i></span>-limonene and <span class="inline-formula"><i>o</i></span>-cresol, consistent with previous findings. The near-molecular EESI response factors were derived from intercomparisons with Vocus-PTR measurements and were found to vary from 10<span class="inline-formula">³</span> to 10<span class="inline-formula">⁶</span> ion counts s<span class="inline-formula">⁻¹</span> ppb<span class="inline-formula">⁻¹</span>, mostly within <span class="inline-formula">±1</span> order of magnitude of their geometric mean of 10<span class="inline-formula">^4.6</span> ion counts s<span class="inline-formula">⁻¹</span> ppb<span class="inline-formula">⁻¹</span>. For aromatic SOA components, the EESI response factors correlated with molecular weight and oxygen content and inversely correlated with volatility. The near-molecular response factors mostly agreed within a factor of 20 for isomers observed across the aromatics and biogenic systems. Parameterization of the near-molecular response factors based on the measured elemental formulae could reproduce the empirically determined response factor for a single volatile organic compound (VOC) system to within a factor of 5 for the configuration of our mass spectrometers. The results demonstrate that standard-free quantification using the EESI-TOF is possible.</p>

P. E. Sheese, K. A. Walker, C. D. Boone et al.

<p>In order to validate satellite measurements of atmospheric composition, it is necessary to understand the range of random and systematic uncertainties inherent in the measurements. On occasions where measurements from two different satellite instruments do not agree within those estimated uncertainties, a common explanation is that the difference can be assigned to geophysical variability, i.e., differences due to sampling the atmosphere at different times and locations. However, the expected geophysical variability is often left ambiguous and rarely quantified. This paper describes a case study where the geophysical variability of O<span class="inline-formula">₃</span> between two satellite instruments – ACE-FTS (Atmospheric Chemistry Experiment – Fourier Transform Spectrometer) and OSIRIS (Optical Spectrograph and InfraRed Imaging System) – is estimated using simulations from climate models. This is done by sampling the models CMAM (Canadian Middle Atmosphere Model), EMAC (ECHAM/MESSy Atmospheric Chemistry), and WACCM (Whole Atmosphere Community Climate Model) throughout the upper troposphere and stratosphere at times and geolocations of coincident ACE-FTS and OSIRIS measurements. Ensemble mean values show that in the lower stratosphere, O<span class="inline-formula">₃</span> geophysical variability tends to be independent of the chosen time coincidence criterion, up to within 12 h; and conversely, in the upper stratosphere geophysical variation tends to be independent of the chosen distance criterion, up to within 2000 km. It was also found that in the lower stratosphere, at altitudes where there is the greatest difference between air composition inside and outside the polar vortex, the geophysical variability in the southern polar region can be double of that in the northern polar region. This study shows that the ensemble mean estimates of geophysical variation can be used when comparing data from two satellite instruments to optimize the coincidence criteria, allowing for the use of more coincident profiles while providing an estimate of the geophysical variation within the comparison results.</p>

S. Noël, M. Reuter, M. Buchwitz et al.

<p>Since 2009, the Greenhouse gases Observing SATellite (GOSAT) has performed radiance measurements in the near-infrared (NIR) and shortwave infrared (SWIR) spectral region. From February 2019 onward, data from GOSAT-2 have also been available.</p> <p>We present the first results from the application of the Fast atmOspheric traCe gAs retrievaL (FOCAL) algorithm to derive column-averaged dry-air mole fractions of carbon dioxide (<span class="inline-formula">XCO₂</span>) from GOSAT and GOSAT-2 radiances and their validation. FOCAL was initially developed for OCO-2 <span class="inline-formula">XCO₂</span> retrievals and allows simultaneous retrievals of several gases over both land and ocean. Because FOCAL is accurate and numerically very fast, it is currently being considered as a candidate algorithm for the forthcoming European anthropogenic <span class="inline-formula">CO₂</span> Monitoring (CO2M) mission to be launched in 2025.</p> <p>We present the adaptation of FOCAL to GOSAT and discuss the changes made and GOSAT specific additions. This particularly includes modifications in pre-processing (e.g. cloud detection) and post-processing (bias correction and filtering).</p> <p><span id="page3838"/>A feature of the new application of FOCAL to GOSAT and GOSAT-2 is the independent use of both S- and P-polarisation spectra in the retrieval. This is not possible for OCO-2, which measures only one polarisation direction. Additionally, we make use of GOSAT's wider spectral coverage compared to OCO-2 and derive not only <span class="inline-formula">XCO₂</span>, water vapour (<span class="inline-formula">H₂O</span>), and solar-induced fluorescence (SIF) but also methane (<span class="inline-formula">XCH₄)</span>, with the potential for further atmospheric constituents and parameters like semi-heavy water vapour (<span class="inline-formula">HDO</span>). In the case of GOSAT-2, the retrieval of nitrous oxide (<span class="inline-formula">XN₂O</span>) and carbon monoxide (<span class="inline-formula">CO</span>) may also be possible.</p> <p>Here, we concentrate on the new FOCAL <span class="inline-formula">XCO₂</span> data products. We describe the generation of the products as well as applied filtering and bias correction procedures. GOSAT-FOCAL <span class="inline-formula">XCO₂</span> data have been produced for the time interval 2009 to 2019. Comparisons with other independent GOSAT data sets reveal agreement of long-term temporal variations within about 1 <span class="inline-formula">ppm</span> over 1 decade; differences in seasonal variations of about 0.5 <span class="inline-formula">ppm</span> are observed. Furthermore, we obtain a station-to-station bias of the new GOSAT-FOCAL product to the ground-based Total Carbon Column Observing Network (TCCON) of 0.56 <span class="inline-formula">ppm</span> with a mean scatter of 1.89 <span class="inline-formula">ppm</span>.</p> <p>The GOSAT-2-FOCAL <span class="inline-formula">XCO₂</span> product is generated in a similar way as the GOSAT-FOCAL product, but with adapted settings. All GOSAT-2 data until the end of 2019 have been processed. Because of this limited time interval, the GOSAT-2 results are considered to be preliminary only, but first comparisons show that these data compare well with the GOSAT-FOCAL results and also TCCON.</p>

L. E. Kalnajs, S. M. Davis, J. D. Goetz et al.

<p>The tropical tropopause layer (TTL; 14–18.5 km) is the gateway for most air entering the stratosphere, and therefore processes within this layer have an outsized influence in determining global stratospheric ozone and water vapor concentrations. Despite the importance of this layer there are few in situ measurements with the necessary detail to resolve the fine-scale processes within this region. Here, we introduce a novel platform for high-resolution in situ profiling that lowers and retracts a suspended instrument package beneath drifting long-duration balloons in the tropics. During a 100 d circumtropical flight, the instrument collected over a hundred 2 km profiles of temperature, water vapor, and aerosol at 1 m resolution, yielding unprecedented geographic sampling and vertical resolution. The instrument system integrates proven sensors for water vapor, temperature, pressure, and cloud and aerosol particles with an innovative mechanical reeling and control system. A technical evaluation of the system performance demonstrated the feasibility of this new measurement platform for future missions with minor modifications. Six instruments planned for two upcoming field campaigns are expected to provide over 4000 profiles through the TTL, quadrupling the number of high-resolution aircraft and balloon profiles collected to date. These and future measurements will provide the necessary resolution to diagnose the importance of competing mechanisms for the transport of water vapor across the TTL.</p>

X. Wang, X. Wang, X. Zhang et al.

<p>An improved two-sphere integration (TSI) technique has been developed to quantify black carbon (BC) concentrations in the atmosphere and seasonal snow. The major advantage of this system is that it combines two distinct integrated spheres to reduce the scattering effect due to light-absorbing particles and thus provides accurate determinations of total light absorption from BC collected on Nuclepore filters. The TSI technique can be calibrated using a series of 15 filter samples of standard fullerene soot. This technique quantifies the mass of BC by separating the spectrally resolved total light absorption into BC and non-BC fractions. To assess the accuracy of the improved system, an empirical procedure for measuring BC concentrations with a two-step thermal–optical method is also applied. Laboratory results indicate that the BC concentrations determined using the TSI technique and theoretical calculations are well correlated (<span class="inline-formula"><i>R</i>²=0.99</span>), whereas the thermal–optical method underestimates BC concentrations by 35&thinsp;%–45&thinsp;% compared to that measured by the TSI technique. Assessments of the two methods for atmospheric and snow samples revealed excellent agreement, with least-squares regression lines with slopes of 1.72 (<span class="inline-formula"><i>r</i>²=0.67</span>) and 0.84 (<span class="inline-formula"><i>r</i>²=0.93</span>), respectively. However, the TSI technique is more accurate in quantifications of BC concentrations in both the atmosphere and seasonal snow, with an overall lower uncertainty. Using the improved TSI technique, we find that light absorption at a wavelength of 550&thinsp;nm due to BC plays a dominant role relative to non-BC light absorption in both the atmosphere (62.76&thinsp;%–91.84&thinsp;% of total light absorption) and seasonal snow (43.11&thinsp;%–88.56&thinsp;%) over northern China.</p>

Iradatul Hanis Abd Hamid, Nathan Narendrannathan, Lee Eng Choy et al.

E. Papandrea, E. Papandrea, S. Casadio et al.

<p>Atmospheric gravity waves generated downstream by orography in a stratified airflow are known as lee waves. In the present study, such mesoscale patterns have been detected, over water and in clear-sky conditions, using the Advanced Infra-Red WAter Vapour Estimator (AIRWAVE) total column water vapour (TCWV) dataset, which contains about 20 years of day and night products, obtained from the thermal infrared measurements of the Along Track Scanning Radiometer (ATSR) instrument series. The high accuracy of such data, along with the native 1&thinsp;km<span class="inline-formula">×1</span>&thinsp;km spatial resolution, allows the investigation of small-scale features such as lee waves. In this work, we focused on the Mediterranean Sea, the largest semi-enclosed basin on the Earth. The peculiarities of this area, which is characterised by complex orography and rough coastlines, lead to the development of these structures over both land and sea. We developed an automatic tool for the rapid detection of areas with high probability of lee wave occurrence, exploiting the TCWV variability in spatial regions with a <span class="inline-formula"><math xmlns="http://www.w3.org/1998/Math/MathML" id="M2" display="inline" overflow="scroll" dspmath="mathml"><mrow><mn mathvariant="normal">0.15</mn><msup><mi/><mo>∘</mo></msup><mo>×</mo><mn mathvariant="normal">0.15</mn><msup><mi/><mo>∘</mo></msup></mrow></math><span><svg:svg xmlns:svg="http://www.w3.org/2000/svg" width="64pt" height="11pt" class="svg-formula" dspmath="mathimg" md5hash="ee0891df08a2383d412e7b879dfcc029"><svg:image xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="amt-12-6683-2019-ie00001.svg" width="64pt" height="11pt" src="amt-12-6683-2019-ie00001.png"/></svg:svg></span></span> area. Through this analysis, several occurrences of structures connected with lee waves have been observed. The waves are detected in spring, autumn and summer seasons, with TCWV values usually falling in the range of 15 to 35&thinsp;kg&thinsp;m<span class="inline-formula">⁻²</span>. In this article, we describe some cases over the central (Italy) and the Eastern Mediterranean Basin (Greece, Turkey and Cyprus). We compared a case of perturbed AIRWAVE TCWV fields due to lee waves occurring over the Tyrrhenian Sea on 18 July 1997 with the sea surface winds from the synthetic aperture radar (SAR), which sounded the same geographical area, finding a good agreement. Another case has been investigated in detail: on 2 August 2002 the Aegean Sea region was almost simultaneously sounded by both the second sensor of the ATSR series (ATSR-2) and the Advanced ATSR (AATSR) instruments. The AIRWAVE TCWV fields derived from the two sensors were successfully compared with the vertically integrated water vapour content simulated with the Weather Research and Forecasting (WRF) numerical model for the same time period, confirming our findings. Wave parameters such as amplitude, wavelength and phase are described through the use of the Morlet continuous wavelet transformation (CWT). The performed analysis derived typical wavelengths from 6 to 8&thinsp;km and amplitudes of up to 20&thinsp;kg&thinsp;m<span class="inline-formula">⁻²</span>.</p>

C. Malings, R. Tanzer, R. Tanzer et al.

<p>Assessing the intracity spatial distribution and temporal variability in air quality can be facilitated by a dense network of monitoring stations. However, the cost of implementing such a network can be prohibitive if traditional high-quality, expensive monitoring systems are used. To this end, the Real-time Affordable Multi-Pollutant (RAMP) monitor has been developed, which can measure up to five gases including the criteria pollutant gases carbon monoxide (CO), nitrogen dioxide (<span class="inline-formula">NO₂</span>), and ozone (<span class="inline-formula">O₃</span>), along with temperature and relative humidity. This study compares various algorithms to calibrate the RAMP measurements including linear and quadratic regression, clustering, neural networks, Gaussian processes, and hybrid random forest–linear regression models. Using data collected by almost 70 RAMP monitors over periods ranging up to 18 months, we recommend the use of limited quadratic regression calibration models for CO, neural network models for NO, and hybrid models for <span class="inline-formula">NO₂</span> and <span class="inline-formula">O₃</span> for any low-cost monitor using electrochemical sensors similar to those of the RAMP. Furthermore, generalized calibration models may be used instead of individual models with only a small reduction in overall performance. Generalized models also transfer better when the RAMP is deployed to other locations. For long-term deployments, it is recommended that model performance be re-evaluated and new models developed periodically, due to the noticeable change in performance over periods of a year or more. This makes generalized calibration models even more useful since only a subset of deployed monitors are needed to build these new models. These results will help guide future efforts in the calibration and use of low-cost sensor systems worldwide.</p>

R. Hann, M. Hermanson

<p>Sampling the atmosphere to analyze contaminants is different from other environmental matrices because measuring the volume of air collected requires a mechanical flow-through device to draw the air and measure its flow rate. The device used must have the capability of concentrating the analytes of interest onto a different substrate because the volumes of air needed are often on the order of hundreds of cubic meters. The use of high-volume air samplers has grown since 1967, when recommended limits of a large number of organic contaminants in air were developed. Equations used for calculating the air flow through the device over time have similarly been developed. However, the complete derivation of those equations has never appeared in the scientific literature. Here a thorough derivation of those equations is provided with definitions of the mechanical systems that are used in the process, along with the method of calibrating and calculating air flow.</p>

J. Gliß, J. Gliß, J. Gliß et al.

Accurate gas velocity measurements in emission plumes are highly desirable for various atmospheric remote sensing applications. The imaging technique of UV SO₂ cameras is commonly used to monitor SO₂ emissions from volcanoes and anthropogenic sources (e.g. power plants, ships). The camera systems capture the emission plumes at high spatial and temporal resolution. This allows the gas velocities in the plume to be retrieved directly from the images. The latter can be measured at a pixel level using optical flow (OF) algorithms. This is particularly advantageous under turbulent plume conditions. However, OF algorithms intrinsically rely on contrast in the images and often fail to detect motion in low-contrast image areas. We present a new method to identify ill-constrained OF motion vectors and replace them using the local average velocity vector. The latter is derived based on histograms of the retrieved OF motion fields. The new method is applied to two example data sets recorded at Mt Etna (Italy) and Guallatiri (Chile). We show that in many cases, the uncorrected OF yields significantly underestimated SO₂ emission rates. We further show that our proposed correction can account for this and that it significantly improves the reliability of optical-flow-based gas velocity retrievals. <br><br> In the case of Mt Etna, the SO₂ emissions of the north-eastern crater are investigated. The corrected SO₂ emission rates range between 4.8 and 10.7 kg s⁻¹ (average of 7.1  ±  1.3 kg s⁻¹) and are in good agreement with previously reported values. For the Guallatiri data, the emissions of the central crater and a fumarolic field are investigated. The retrieved SO₂ emission rates are between 0.5 and 2.9 kg s⁻¹ (average of 1.3  ±  0.5 kg s⁻¹) and provide the first report of SO₂ emissions from this remotely located and inaccessible volcano.

A. Lambe, A. Lambe, P. Massoli et al.

Oxidation flow reactors that use low-pressure mercury lamps to produce hydroxyl (OH) radicals are an emerging technique for studying the oxidative aging of organic aerosols. Here, ozone (O₃) is photolyzed at 254 nm to produce O(¹D) radicals, which react with water vapor to produce OH. However, the need to use parts-per-million levels of O₃ hinders the ability of oxidation flow reactors to simulate NO_<i>x</i>-dependent secondary organic aerosol (SOA) formation pathways. Simple addition of nitric oxide (NO) results in fast conversion of NO_<i>x</i> (NO + NO₂) to nitric acid (HNO₃), making it impossible to sustain NO_<i>x</i> at levels that are sufficient to compete with hydroperoxy (HO₂) radicals as a sink for organic peroxy (RO₂) radicals. We developed a new method that is well suited to the characterization of NO_<i>x</i>-dependent SOA formation pathways in oxidation flow reactors. NO and NO₂ are produced via the reaction O(¹D) + N₂O  →  2NO, followed by the reaction NO + O₃  →  NO₂ + O₂. Laboratory measurements coupled with photochemical model simulations suggest that O(¹D) + N₂O reactions can be used to systematically vary the relative branching ratio of RO₂ + NO reactions relative to RO₂ + HO₂ and/or RO₂ + RO₂ reactions over a range of conditions relevant to atmospheric SOA formation. We demonstrate proof of concept using high-resolution time-of-flight chemical ionization mass spectrometer (HR-ToF-CIMS) measurements with nitrate (NO₃⁻) reagent ion to detect gas-phase oxidation products of isoprene and <i>α</i>-pinene previously observed in NO_<i>x</i>-influenced environments and in laboratory chamber experiments.

V. Caicedo, B. Rappenglück, B. Lefer et al.

Three algorithms for estimating the boundary layer heights are assessed: an aerosol gradient method, a cluster analysis method, and a Haar wavelet method. Over 40 daytime clear-sky radiosonde profiles are used to compare aerosol backscatter boundary layer heights retrieved by a Vaisala CL31 ceilometer. Overall good agreement between radiosonde- and aerosol-derived boundary layer heights was found for all methods. The cluster method was found to be particularly sensitive to noise in ceilometer signals and lofted aerosol layers (48.8 % of comparisons), while the gradient method showed limitations in low-aerosol-backscatter conditions. The Haar wavelet method was demonstrated to be the most robust, only showing limitations in 22.5 % of all observations. Occasional differences between thermodynamically and aerosol-derived boundary layer heights were observed.

J. Kangasluoma, A. Franchin, J. Duplissy et al.

Measuring sub-3 nm particles outside of controlled laboratory conditions is a challenging task, as many of the instruments are operated at their limits and are subject to changing ambient conditions. In this study, we advance the current understanding of the operation of the Airmodus A11 nano Condensation Nucleus Counter (nCNC), which consists of an A10 Particle Size Magnifier (PSM) and an A20 Condensation Particle Counter (CPC). The effect of the inlet line pressure on the measured particle concentration was measured, and two separate regions inside the A10, where supersaturation of working fluid can take place, were identified. The possibility of varying the lower cut-off diameter of the nCNC was investigated; by scanning the growth tube temperature, the range of the lower cut-off was extended from 1–2.5 to 1–6 nm. Here we present a new inlet system, which allows automated measurement of the background concentration of homogeneously nucleated droplets, minimizes the diffusion losses in the sampling line and is equipped with an electrostatic filter to remove ions smaller than approximately 4.5 nm. Finally, our view of the guidelines for the optimal use of the Airmodus nCNC is provided.

J. B. Wu, X. Y. Zhou, A. Z. Wang et al.

Eddy covariance using infrared gas analyzes has been a useful tool for gas exchange measurements between soil, vegetation and the atmosphere. So far, comparisons between the open- and closed-path eddy covariance (CP) system have been extensively made on CO₂ flux estimations, while lacking in the comparison of water vapor flux estimations. In this study, the specific performance of water vapor flux measurements of an open-path eddy covariance (OP) system was compared against a CP system over a tall temperate forest in northeastern China. The results show that the fluxes from the OP system (<i>LE</i>_op) were generally greater than the <i>LE</i>_cp though the two systems shared one sonic anemometer. The tube delay of closed-path analyzer depended on relative humidity, and the fixed median time lag contributed to a significant underestimation of <i>LE</i>_cp between the forest and atmosphere, while slight systematic overestimation was also found for covariance maximization method with single broad time lag search window. After the optimized time lag compensation was made, the average difference between the 30 min <i>LE</i>_op and <i>LE</i>_cp was generally within 6.0 %. Integrated over the annual cycle, the CP system yielded a 5.1 % underestimation of forest evapotranspiration as compared to the OP system measurements (493 vs. 469 mm yr^&minus;1). This study indicates the importance to estimate the sampling tube delay accurately for water vapor flux calculations with closed-path analyzers, and it also suggests that some of the imbalance of the surface energy budget in flux sites is possibly caused by the systematic underestimation of water vapor fluxes measured with closed-path eddy covariance systems.

A. Réchou, T. Narayana Rao, O. Bousquet et al.

The microphysical properties of rainfall at the island of Réunion are analysed and quantified according to one year of wind profiler observations collected at Saint-Denis international airport. The statistical analysis clearly shows important differences in rain vertical profiles as a function of the seasons. During the dry season, the vertical structure of precipitation is driven by trade wind and boundary-layer inversions, both of which limit the vertical extension of the clouds. The rain rate is lower than 2.5 mm h⁻¹ throughout the lower part of the troposphere (about 2 km) and decreases in the higher altitudes. During the moist season, the average rain rate is around 5 mm h⁻¹ and nearly uniform from the ground up to 4 km. <br><br> The dynamical and microphysical properties (including drop size distributions) of four distinct rainfall events are also investigated through the analysis of four case studies representative of the variety of rain events occurring on Réunion: summer deep convection, northerly-to-northeasterly flow atmospheric pattern, cold front and winter depression embedded in trade winds. Radar-derived rain parameters are in good agreement with those obtained from collocated rain gauge observations in all cases, which demonstrates that accurate qualitative and quantitative analysis can be inferred from wind profiler data. Fluxes of kinetic energy are also estimated from wind profiler observations in order to evaluate the impact of rainfall on soil erosion. Results show that horizontal kinetic energy fluxes are systematically one order of magnitude higher than vertical kinetic energy fluxes. A simple relationship between the reflectivity factor and vertical kinetic energy fluxes is proposed based on the results of the four case studies.

A. Schladitz, M. Merkel, S. Bastian et al.

An automated function control unit was developed to regularly check the ambient particle number concentration derived from a mobility particle size spectrometer as well as its zero-point behaviour. The function control allows unattended quality assurance experiments at remote air quality monitoring or research stations under field conditions. The automated function control also has the advantage of being able to get a faster system stability response than the recommended on-site comparisons with reference instruments. The method is based on a comparison of the total particle number concentration measured by a mobility particle size spectrometer and a condensation particle counter while removing diffusive particles smaller than 20 nm in diameter. In practice, the small particles are removed by a set of diffusion screens, as traditionally used in a diffusion battery. Another feature of the automated function control is to check the zero-point behaviour of the ambient aerosol passing through a high-efficiency particulate air (HEPA) filter. <br><br> The performance of the function control is illustrated with the aid of a 1-year data set recorded at Annaberg-Buchholz, a station in the Saxon air quality monitoring network. During the period of concern, the total particle number concentration derived from the mobility particle size spectrometer slightly overestimated the particle number concentration recorded by the condensation particle counter by 2 % (grand average). Based on our first year of experience with the function control, we developed tolerance criteria that allow a performance evaluation of a tested mobility particle size spectrometer with respect to the total particle number concentration. We conclude that the automated function control enhances the quality and reliability of unattended long-term particle number size distribution measurements. This will have beneficial effects for intercomparison studies involving different measurement sites, and help provide a higher data accuracy for cohort health and climate research studies.