Mohammed Iqbal Mead

A lightweight near-infrared spectrometer for the detection of trace atmospheric species

This paper describes the development and deployment of a lightweight in situ near-infrared tunable diode laser absorption spectrometer (TDLAS) for balloon-borne measurements of trace species such as methane in the upper troposphere and stratosphere. The key feature of the instrument design is its ability to provide high sensitivity measurements with better than 1 part in 10(6) Hz(-1/2) optical sensitivity in a lightweight package weighing as little as 6 kg, and maintaining this level of performance over the wide range of conditions experienced during field measurements. The absolute accuracy for methane measurements is approximately 10% limited by uncertainties in determining the gas temperature in the measurement volume. The high sensitivity and high temporal resolution (2.3 s measurement period) enables details of the fine-scale structure in the atmosphere to be measured. The TDLAS instrument has been used on a number of major international measurement campaigns. Intercomparison with other instruments during these campaigns have confirmed the comparability of the results from this instrument with measurements made by a range of other techniques, and demonstrated the instruments suitability for studies of atmospheric dynamics, transport, and mixing processes.

Infrared Atmospheric Sounding Interferometer correlation interferometry for the retrieval of atmospheric gases: the case of H 2 O and CO 2

Correlation interferometry is a particular application of Fourier transform spectroscopy with partially scanned interferograms. Basically, it is a technique to obtain the difference between the spectra of atmospheric radiance at two diverse spectral resolutions. Although the technique could be exploited to design an appropriate correlation interferometer, in this paper we are concerned with the analytical aspects of the method and its application to high-spectral-resolution infrared observations in order to separate the emission of a given atmospheric gas from a spectral signal dominated by surface emission, such as in the case of satellite spectrometers operated in the nadir looking mode. The tool will be used to address some basic questions concerning the vertical spatial resolution of H2O and to develop an algorithm to retrieve the columnar amount of CO2. An application to complete interferograms from the Infrared Atmospheric Sounding Interferometer will be presented and discussed. For H2O, we have concluded that the vertical spatial resolution in the lower troposphere mostly depends on broad features associated with the spectrum, whereas for CO2, we have derived a technique capable of retrieving a CO2 columnar amount with accuracy of ≈±7 parts per million by volume at the level of each single field of view.

Stable carbon isotope analysis of selected halocarbons at parts per trillion concentration in an urban location

Environmental Context. Halocarbons can have significant effects on the atmosphere and the environment, particularly with regard to ozone depletion and climate change impacts. The determination of isotopic concentrations for selected halocarbon species should provide useful information to identify and constrain halocarbon sources and sinks within the urban environment. In the present study, a new instrumental method is described to determine these isotope ratios for selected halocarbons and the resultant data are interpreted in terms of local sources and sinks. Abstract. δ13C values of a suite of halocarbons have been determined in an urban background site in Bristol, UK. A novel mobile preconcentration system, based on the use of multi-adsorbent sample tubes, has been developed for trapping relatively large-volume air samples in potentially remote areas. An Adsorption Desorption System–Gas Chromatography–Electron Capture Detector was used to measure the mixing ratios of the selected halocarbon species, while a Gas Chromatography–Combustion–Isotope Ratio Mass Spectrometer was used to determine δ13C values. For the species with strong local sources, the variation of isotope ratios has been observed over the experimental period. Some of the results reported in the present study differ from previously reported values and reasons for this are discussed. The reporting of different δ13C values for selected halocarbons from different areas in the present study suggests that δ13C values may be used to determine the relative magnitudes of anthropogenic and biogenic sources.

Leaf Cutter Ants: A Possible missing source of biogenic halocarbons

Environmental context. With large reductions in anthropogenic emissions of many ozone-depleting gases in response to the Montreal Protocol, gases with biogenic sources have become relatively more important in recent years. The global budgets of the biogenic halocarbons are unbalanced with known sinks outweighing sources, suggesting that additional natural sources are required to balance the budgets. In the present study, an investigation has been carried out to determine the importance of leaf cutter ants as a missing source of the biogenic halocarbons, which will reduce the discrepancy of the global budget of the halocarbons. Abstract. Leaf cutter ant colonies are shown to be a potentially significant new source of biogenic halocarbons. Fungus cultivated by these ant species may emit CH3Br, CH3I, CH3Cl, CH2Cl2 and CHCl3 in significant quantities, contributing to their respective global atmospheric budgets. The study suggests that the mixing ratios of CH3Br, CH3I, CH3Cl, CH2Cl2 and CHCl3 in the ant colony under test were significantly higher than background levels, by on average a factor of 1.5–5.0. Sampling was carried out during three stages of ant colony development (new, moderately active and highly active) and it was found that levels of these halocarbons were elevated during the active phases of the ant colony life cycle. A very rough estimate of the possible emission of CH3Br, CH3I, CH3Cl, CH2Cl2 and CHCl3 from ant colonies globally are 0.50, 0.02, 0.80, 0.15 and 0.22 Gg year–1.

The development and trial of an unmanned aerial system for the measurement of methane flux from landfill and greenhouse gas emission hotspots

This paper describes the development of a new sampling and measurement method to infer methane flux using proxy measurements of CO2 concentration and wind data recorded by Unmanned Aerial Systems (UAS). The flux method described and trialed here is appropriate to the spatial scale of landfill sites and analogous greenhouse gas emission hotspots, making it an important new method for low-cost and rapid case study quantification of fluxes from currently uncertain (but highly important) greenhouse gas sources. We present a case study using these UAS-based measurements to derive instantaneous methane fluxes from a test landfill site in the north of England using a mass balance model tailored for UAS sampling and co-emitted CO2 concentration as a methane-emission proxy. Methane flux (and flux uncertainty) during two trials on 27 November 2014 and 5 March 2015, were found to be 0.140 kg s-1 (±61% at 1σ), and 0.050 kg s-1 (±54% at 1σ), respectively. Uncertainty contributing to the flux was dominated by ambient variability in the background (inflow) concentration (>40%) and wind speed (>10%); with instrumental error contributing only ∼1-2%. The approach described represents an important advance concerning the challenging problem of greenhouse gas hotspot flux calculation, and offers transferability to a wide range of analogous environments. This new measurement solution could add to a toolkit of approaches to better validate source-specific greenhouse emissions inventories - an important new requirement of the UNFCCC COP21 (Paris) climate change agreement.

Seasonal and long term variations of surface ozone concentrations in Malaysian Borneo

Malaysian Borneo has a lower population density and is an area known for its lush rainforests. However, changes in pollutant profiles are expected due to increasing urbanisation and commercial-industrial activities. This study aims to determine the variation of surface O3 concentration recorded at seven selected stations in Malaysian Borneo. Hourly surface O3 data covering the period 2002 to 2013, obtained from the Malaysian Department of Environment (DOE), were analysed using statistical methods. The results show that the concentrations of O3 recorded in Malaysian Borneo during the study period were below the maximum Malaysian Air Quality Standard of 100ppbv. The hourly average and maximum O3 concentrations of 31 and 92ppbv reported at Bintulu (S3) respectively were the highest among the O3 concentrations recorded at the sampling stations. Further investigation on O3 precursors show that sampling sites located near to local petrochemical industrial activities, such as Bintulu (S3) and Miri (S4), have higher NO2/NO ratios (between 3.21 and 5.67) compared to other stations. The normalised O3 values recorded at all stations were higher during the weekend compared to weekdays (unlike its precursors) which suggests the influence of O3 titration by NO during weekdays. The results also show that there are distinct seasonal variations in O3 across Borneo. High surface O3 concentrations were usually observed between August and September at all stations with the exception of station S7 on the east coast. Majority of the stations (except S1 and S6) have recorded increasing averaged maximum concentrations of surface O3 over the analysed years. Increasing trends of NO2 and decreasing trends of NO influence the yearly averaged maximum of O3 especially at S3. This study also shows that variations of meteorological factors such as wind speed and direction, humidity and temperature influence the concentration of surface O3.