Verification of Angular Response of Sky Quality Meter with Quasi-Punctual Light Sources

Sky Quality Meter (SQM) is a commercial instrument based on photometers widely used by amateur astronomers for skyglow measurement from the ground. In the framework of the MINLU project, two SQM-LE units were integrated in an autonomous sensor suite realized and tested at University of Padova for monitoring light pollution from drones or sounding balloons. During the ground tests campaign before airborne measurement, the performance of both SQM units was verified in laboratory using controlled light sources as a reference input; the results showed that both units presented an angular response deviating consistently from the expected performance and that the sensors’ field of view was larger than the one declared in the manufacturer’s datasheet. This aspect in particular would affect direct skyglow measurements during flight as light sources close to the boundaries of the field of view would not be attenuated but instead detected by the sensors. As a direct consequence, the measurement of low-intensity skyglows at stratospheric altitudes could be affected by high-intensity punctual sources acting as lateral disturbances. A dedicated test campaign was therefore conceived and realized to investigate SQM unit response to light sources in the field of view and identify the true angular response curve; the setup consisted in a controlled rotatory stage moving the unit in front of a fixed diffusive light source. Different test conditions were used to validate the experimental procedure, demonstrating the repeatability of the measurements. This paper presents the experimental campaign and the resulting SQM angular response curve; results indicate for both SQMs a larger than expected field of view and the presence of a double peak in the angular response, which is likely related to a non-perfect alignment of SQMs collimation optics. Furthermore, the wider resulting curves suggest that the contribution of lateral sources is more prominent with respect to the response predicted by the manufacturer. For this reason, the utilization of baffles to restrict SQMs field of view is analyzed to minimize the disturbance of lateral light sources and two different geometries are presented.

Coal seam gas industry methane emissions in the Surat Basin, Australia: comparing airborne measurements with inventories

Coal seam gas (CSG) accounts for about one-quarter of natural gas production in Australia and rapidly increasing amounts globally. This is the first study worldwide using airborne measurement techniques to quantify methane (CH 4 ) emissions from a producing CSG field: the Surat Basin, Queensland, Australia. Spatially resolved CH 4 emissions were quantified from all major sources based on top-down (TD) and bottom-up (BU) approaches, the latter using Australia's UNFCCC reporting workflow. Based on our TD-validated BU inventory, CSG sources emit about 0.4% of the produced gas, comparable to onshore dry gas fields in the USA and The Netherlands, but substantially smaller than in other onshore regions, especially those where oil is co-produced (wet gas). The CSG CH 4 emission per unit of gas production determined in this study is two to three times higher than existing inventories for the region. Our results indicate that the BU emission factors for feedlots and grazing cattle need review, possibly requiring an increase for Queensland's conditions. In some subregions, the BU estimate for gathering and boosting stations is potentially too high. The results from our iterative BU inventory process, which feeds into TD data, illustrate how global characterization of CH 4 emissions could be improved by incorporating empirical TD verification surveys into national reporting. This article is part of a discussion meeting issue ‘Rising methane: is warming feeding warming? (part 1)’.

Field observational constraints on the controllers in glyoxal (CHOCHO) loss to aerosol

Glyoxal (CHOCHO), the simplest dicarbonyl in the troposphere, is an important precursor for secondary organic aerosol (SOA) and brown carbon (BrC) affecting air-quality and climate. The airborne measurement of CHOCHO concentrations during the KORUS-AQ (KORea-US Air Quality study) campaign in 2016 enables detailed quantification of loss mechanisms, pertaining to SOA formation in the real atmosphere. The production of this molecule was mainly from oxidation of aromatics (59 %) initiated by hydroxyl radical (OH), of which glyoxal forming mechanisms are relatively well constrained. CHOCHO loss to aerosol was found to be the most important removal path (69 %) and contributed to roughly ~20 % (3.7 μg sm−3 ppmv−1 hr−1, normalized with excess CO) of SOA growth in the first 6 hours in Seoul Metropolitan Area. To our knowledge, we show the first field observation of aerosol surface-area (Asurf)-dependent CHOCHO uptake, which diverges from the simple surface uptake assumption as Asurf increases in ambient condition. Specifically, under the low (high) aerosol loading, the CHOCHO effective uptake rate coefficient, keff,uptake, linearly increases (levels off) with Asurf, thus, the irreversible surface uptake is a reasonable (unreasonable) approximation for simulating CHOCHO loss to aerosol. Dependency of photochemical impact, as well as aerosol viscosity, are discussed as other possible factors influencing CHOCHO uptake rate. Our inferred Henry's law coefficient of CHOCHO, 7.0 × 108 M atm−1, is ~2 orders of magnitude higher than those estimated from salting-in effects constrained by inorganic salts only, which urges more understanding on CHOCHO solubility under real atmospheric conditions.

Ultra-Light Airborne Measurement System for Investigation of Urban Boundary Layer Dynamics

Winter smog episodes are a severe problem in many cities around the world. The following two mechanisms are responsible for influencing the level of pollutant concentrations: emission of pollutants from different sources and associated processes leading to formation of secondary aerosols in the atmosphere and meteorology, including advection, which is stimulated by horizontal wind, and convection, which depends on vertical air mass movements associated with boundary layer stability that are determined by vertical temperature and humidity gradients. The aim of the present study was to evaluate the performance of an unmanned aerial vehicle (UAV)-based measurement system developed for investigation of urban boundary layer dynamics. The evaluation was done by comparing the results of temperature, relative humidity, wind speed and particulate matter fraction with aerodynamic diameter below 10 μm (PM10) concentration vertical profiles obtained using this system with two reference meteorological stations: Jagiellonian University Campus (JUC) and radio transmission tower (RTCN), located in the urban area of Krakow city, Southern Poland. The secondary aim of the study was to optimize data processing algorithms improving the response time of UAV sensor measurements during the ascent and descent parts of the flight mission.

A Two-Day Case Study: Comparison of Turbulence Data from an Unmanned Aircraft System with a Model Chain for Complex Terrain

The airborne measurement platform MASC-3 (Multi-Purpose Airborne Sensor Carrier) is used for measurements over a forested escarpment in the Swabian Alps to evaluate the wind field. Data from flight legs between 20 and 200 m above the ground on two consecutive days with uphill (westerly) flow in September 2018 are analyzed. In the lowest 140 m above the ground a speed-up is found with increased turbulence and changes in wind direction directly over the escarpment, whereas in the lowest 20 to 50 m above the ground a deceleration of the flow is measured. Additionally, simulation results from a numerical model chain based on the Weather Research and Forecasting (WRF) model and an OpenFOAM (Open Source Field Operation and Manipulation) model, developed for complex terrain, are compared to the data captured by MASC-3. The models and measurements compare well for the mean wind speed and inclination angle.

Method for airborne measurement of the spatial wind speed distribution above complex terrain

Wind farm sites in complex terrain are subject to local wind phenomena, which have a relevant impact on a wind turbine's annual energy production. To reduce investment risk, an extensive site evaluation is therefore mandatory. Stationary long-term measurements are supplemented by computational fluid dynamics (CFD) simulations, which are a commonly used tool to analyse and understand the three-dimensional wind flow above complex terrain. Though under intensive research, such simulations still show a high sensitivity to various input parameters like terrain, atmosphere and numerical setup. In this paper, a different approach aims to measure instead of simulate wind speed deviations above complex terrain by using a flexible, airborne measurement system. An unmanned aerial vehicle is equipped with a standard ultrasonic anemometer. The uncertainty in the system is evaluated against stationary anemometer data at different heights and shows very good agreement, especially in mean wind speed (< 0.12 m s−1) and mean direction (< 2.4∘) estimation. A test measurement was conducted above a forested and hilly site to analyse the spatial and temporal variability in the wind situation. A position-dependent difference in wind speed increase of up to 30 % compared to a stationary anemometer is detected.

Autonomous airborne mid-infrared spectrometer for high-precision measurements of ethane during the NASA ACT-America studies

An airborne trace gas sensor based on mid-infrared technology is presented for fast (1 s) and high-precision ethane measurements during the Atmospheric Carbon and Transport-America (ACT-America) study. The ACT-America campaign is a multiyear effort to better understand and quantify sources and sinks for the two major greenhouse gases carbon dioxide and methane. Simultaneous airborne ethane and methane measurements provide one method by which sources of methane can be identified and quantified. The instrument described herein was operated on NASA's B200 King Air airplane spanning five separate field deployments. As this platform has limited payload capabilities, considerable effort was devoted to minimizing instrument weight and size without sacrificing airborne ethane measurement performance. This paper describes the numerous features designed to achieve these goals. Two of the key instrument features that were realized were autonomous instrument control with no onboard operator and the implementation of direct absorption spectroscopy based on fundamental first principles. We present airborne measurement performance for ethane based upon the precisions of zero air background measurements and ambient precision during quiescent stable periods. The airborne performance was improved with each successive deployment phase, and we summarize the major upgraded design features to achieve these improvements. During the fourth deployment phase in the spring of 2018, the instrument achieved 1 s (1σ) airborne ethane precisions reproducibly in the 30–40 parts per trillion by volume (pptv) range in both the boundary layer and the less turbulent free troposphere. This performance is among some of the best reported to date for fast (1 Hz) airborne ethane measurements. In both the laboratory conditions and at times during calm and level airborne operation, these precisions were as low as 15–20 pptv.

Autonomous Airborne Mid-IR Spectrometer for High Precision Measurements of Ethane during the NASA ACT-America Studies

An airborne trace gas sensor based on mid-infrared technology is presented for fast (1-second) and high precision ethane measurements during the Atmospheric Carbon and Transport-America (ACT-America) study. The ACT-America campaign is a multi-year effort to better understand and quantify sources and sinks for the two major greenhouse gases carbon dioxide and methane. Simultaneous airborne ethane and methane measurements provide one method by which sources of methane can be identified and quantified. The instrument described herein was operated on NASA's B200 King Air airplane spanning five separate field deployments. As this platform has limited payload capabilities, considerable effort was devoted to minimizing instrument weight and size without sacrificing airborne ethane measurement performance. This paper describes the numerous features designed to achieve these goals. Two of the key instrument features that were realized were autonomous instrument control with no on-board operator and the implementation of direct absorption spectroscopy based on fundamental first principles. We present airborne measurement performance for ethane based upon the precisions of zero air background measurements as well as ambient precision during quiescent stable periods. The airborne performance was improved with each successive deployment phase, and we summarize the major upgraded design features to achieve these improvements. During the 4th deployment phase, in the spring of 2018, the instrument achieved 1-second (1σ) airborne ethane precisions reproducibly in the 30–40 parts-per-trillion by volume (pptv) range in both the boundary layer and the less turbulent free troposphere. This performance is among some of the best reported to date for fast (1 Hz) airborne ethane measurements. In both the laboratory conditions and at times during calm and level airborne operation these precisions were as low as 15–20 pptv.

Comparison of Airborne Peroxy Radical Measurements with MECO(n) model simulation during EMeRGe in Europe

&lt;p&gt;Observations of tropospheric peroxy radicals are a key point for interpretation of the processing and transformation of polluted outflows from major populated centres (MPCs). A series of European MPCs are investigated by the project EMeRGe (Effect of Megacities on the transport and transformation of pollutants on the Regional and Global scales). With this objective two airborne campaigns using the research platform HALO (High Altitude and LOng range aircraft) were carried out over Europe in summer 2017 and over east Asia in the intermonsoon period in 2018. The Institute of Environmental Physics (IUP) in Bremen (Germany) participated in both EMeRGe campaigns with the airborne measurement of the total sum of peroxy radicals, RO&lt;sub&gt;2&lt;/sub&gt;&lt;sup&gt;*&lt;/sup&gt;, by using &amp;#160;the home made PeRCEAS instrument based on the combination of the PERCA (peroxy radical chemical amplification)&amp;#160; and CRDS (cavity ring down spectroscopy) techniques. One of the main purposes of the campaigns was the investigation of the characteristics and chemical transformation of MPC outflows at the local and regional scales.&lt;/p&gt;&lt;p&gt;During the EMeRGe campaign in Europe, air masses of different photochemical activity were measured, where RO&lt;sub&gt;2&lt;/sub&gt;&lt;sup&gt;*&lt;/sup&gt; mixing ratios up to 100pptv being observed. In the present study the RO&lt;sub&gt;2&lt;/sub&gt;&lt;sup&gt;* &lt;/sup&gt;observations for six measurement flights of EMeRGe in Europe have been compared with RO&lt;sub&gt;2&lt;/sub&gt; (here defined as the sum of HO&lt;sub&gt;2 &lt;/sub&gt;+ CH&lt;sub&gt;3&lt;/sub&gt;O&lt;sub&gt;2 &lt;/sub&gt;+ ISOOH + CH&lt;sub&gt;3&lt;/sub&gt;CO&lt;sub&gt;3 &lt;/sub&gt;+ CH&lt;sub&gt;3&lt;/sub&gt;COCH&lt;sub&gt;2&lt;/sub&gt;O&lt;sub&gt;2&lt;/sub&gt;) simulated by using the MECO(n) model.&lt;/p&gt;&lt;p&gt;MECO(n) (MESSy-fied ECHAM and COSMO models nested n times), is &amp;#160;a global/regional chemistry-climate model developed by the MESSy consortium, which couples on-line the global chemistry-climate model EMAC with the regional chemistry-climate model COSMO-CLM/MESSy. The same anthropogenic emission inventory (EDGAR 4.3.1) as well as the same solver for chemical kinetics, involving complex tropospheric and stratospheric chemistry, are applied in EMAC and COSMO-CLM/MESSy.&lt;/p&gt;&lt;p&gt;Overall, the agreement between the measurements and model is reasonable for RO&lt;sub&gt;2&lt;/sub&gt;&lt;sup&gt;* &lt;/sup&gt;observations below 40 pptv. Events with higher mixing ratios seem not to be well reproduced by the model but underestimated. Further details on the modelling and the result of the comparison will be presented.&lt;/p&gt;

Methane Source Attribution Challenges in the Surat Basin, Australia

&lt;p&gt;One of the case study sites for the Climate and Clean Air Coalition (CCAC) Methane Science Studies is the coal seam gas (CSG) field in the Surat Basin, Queensland, Australia, where there are over 6000 CSG wells and associated gas and water processing infrastructure. Previous bottom-up estimates suggest that the major source of methane in the region is cattle, not CSG (Katestone, 2018, Luhar et al. 2018).&lt;/p&gt;&lt;p&gt;In September 2018, an airborne measurement campaign was undertaken to provide a top-down estimate of regional methane emissions. Modelling of the airborne methane mole fraction data has produced a defensible total methane emissions estimate. However, there are challenges with proportioning the top-down estimates provided by the airborne data, because of adjacent sources with similar d&lt;sup&gt;13&lt;/sup&gt;C-CH&lt;sub&gt;4&lt;/sub&gt; isotopic chemistry, rapid mixing of adjacent sources and substantial dilution of the plumes at the airborne measurement sampling height. We present how we will overcome these challenges.&lt;/p&gt;&lt;p&gt;At each gas production well, tens of thousands of litres of water are produced daily in association with the methane extracted from the coal measures. This water is stored in ponds and is also used as a water supply for cattle feedlots, which are located throughout and adjacent to the CSG wells and processing facilities. Power stations are also located within the CSG field. This arrangement makes it challenging to obtain clean top-down estimates of the emissions from CSG production. Quantifying methane emissions associated with CSG production is further complicated by numerous other sources of methane in the region immediately adjacent to the CSG field. These sources include grazing cattle, abattoirs, more power production facilities, coal mines, wetlands, natural gas seeps, and small urban centres with associated sewage treatment plants and landfills. Grab bag air samples were collected at each of these sources and analysed for d&lt;sup&gt;13&lt;/sup&gt;C-CH&lt;sub&gt;4, &lt;/sub&gt;d&lt;sup&gt;13&lt;/sup&gt;C-CO&lt;sub&gt;2&lt;/sub&gt; and dD-CH&lt;sub&gt;4&lt;/sub&gt;.&lt;/p&gt;&lt;p&gt;The airborne measurement campaign was undertaken under warm daytime spring conditions. This caused rapid uplift and mixing of the methane plumes. The maximum difference between the lowest and highest methane mole fraction from 90 airborne collected grab bag air samples was only 0.03 ppm. Even at this low mole fraction, by implementing quality management protocols we were able to extract trends in the isotope data sets. This presentation will outline the quality management procedures and how the measurements of d&lt;sup&gt;13&lt;/sup&gt;C-CH&lt;sub&gt;4, &lt;/sub&gt;d&lt;sup&gt;13&lt;/sup&gt;C-CO&lt;sub&gt;2&lt;/sub&gt; and dD-CH&lt;sub&gt;4&lt;/sub&gt; will be used to assist with methane source attribution.&lt;/p&gt;&lt;p&gt;&lt;strong&gt;Reference&lt;/strong&gt;&lt;/p&gt;&lt;p&gt;Katestone Environmental Pty Ltd (2018) Surat Basin Methane Inventory 2015 - Summary Report. Prepared for CSIRO March 2017 (D15193-11).&lt;/p&gt;&lt;p&gt;Luhar, A., Etheridge, D., Loh, Z., Noonan, N., Spencer, D., Day, S. (2018). Characterisation of Regional Fluxes of Methane in the Surat Basin, Queensland. Final report on Task 3: Broad scale application of methane detection, and Task 4: Methane emissions enhanced modelling. Report to the Gas Industry Social and Environmental Research Alliance (GISERA). Report No. EP185211, October 2018. CSIRO Australia.&lt;/p&gt;