Elemental Composition of Suspended Particulate Matter Collected at Two Different Heights above the Ground in A Sub-Urban Site in Kenya

Suspended particulate matter samples were collected in a sub-urban area in Nairobi over a 12 month period at two different heights above ground using a “Gent” SFU sampler. A total of 126 sets of duplicate fine and coarse particulate matter samples were collected. The samples were analysed by energy dispersive x-ray fluorescence (EDXRF) and atomic absorption spectroscopy (AAS) for up to 10 elements. It was found that 66% of the samples collected at two metres and 50% of the samples collected at four metres height exceeded the WHO 24 guideline of 70μg m-3. Reduction in concentration of between 30 to 74 % for Ca, Ti, Zr and Fe were observed both in coarse and fine particulate matter fractions at the higher height. The elements Cu, Zn, Pb and Br represented 0.5 to 1.1 % of the total coarse particulate matter at both heights. Higher proportions of 1.5 to 3.5 % were observed at both heights in the fine particulate matter fraction. High enrichment factors were observed for Cu (10.8 - 228.3), Zn (12.4 - 124.6), Pb (59.4 - 1967) and Br (152.5 - 3038.7) at both heights suggesting anthropogenic activities such as industrial, urban refuse burning, residential and vehicular emissions could be the major contributors. Pb and Br were mainly from the vehicular emissions as indicated by the strong correlations (r > 0.593) and the Br/Pb ratios (0.307 to 0.339).Keywords: Sub-urban, EDXRF, AAS, Enrichment factors, Heavy metals, particulate matter

A westward extension of the warm pool leads to a westward extension of the Walker circulation, drying eastern Africa

Observations and simulations link anthropogenic greenhouse and aerosol emissions with rapidly increasing Indian Ocean sea surface temperatures (SSTs). Over the past 60 years, the Indian Ocean warmed two to three times faster than the central tropical Pacific, extending the tropical warm pool to the west by ~40° longitude (><4,000 km). This propensity toward rapid warming in the Indian Ocean has been the dominant mode of interannual variability among SSTs throughout the tropical Indian and Pacific Oceans (55°E–140°W) since at least 1948, explaining more variance than anomalies associated with the El Niño-Southern Oscillation (ENSO). In the atmosphere, the primary mode of variability has been a corresponding trend toward greatly increased convection and precipitation over the tropical Indian Ocean. The temperature and rainfall increases in this region have produced a westward extension of the western, ascending branch of the atmospheric Walker circulation. Diabatic heating due to increased mid-tropospheric water vapor condensation elicits a westward atmospheric response that sends an easterly flow of dry air aloft toward eastern Africa. In recent decades (1980–2009), this response has suppressed convection over tropical eastern Africa, decreasing precipitation during the ‘long-rains’ season of March–June. This trend toward drought contrasts with projections of increased rainfall in eastern Africa and more ‘El Niño-like’ conditions globally by the Intergovernmental Panel on Climate Change. Increased Indian Ocean SSTs appear likely to continue to strongly modulate the Warm Pool circulation, reducing precipitation in eastern Africa, regardless of whether the projected trend in ENSO is realized. These results have important food security implications, informing agricultural development, environmental conservation, and water resource planning

PolarBRDF: A general purpose Python package for visualization and quantitative analysis of multi-angular remote sensing measurements (vol 96, pg 173, 2016)

The Bidirectional Reflectance Distribution Function (BRDF) is a fundamental concept for characterizing the reflectance property of a surface, and helps in the analysis of remote sensing data from satellite, airborne and surface platforms. Multi-angular remote sensing measurements are required for the development and evaluation of BRDF models for improved characterization of surface properties. However, multi-angular data and the associated BRDF models are typically multidimensional involving multi-angular and multi-wavelength information. Effective visualization of such complex multidimensional measurements for different wavelength combinations is presently somewhat lacking in the literature, and could serve as a potentially useful research and teaching tool in aiding both interpretation and analysis of BRDF measurements. This article describes a newly developed software package in Python (PolarBRDF) to help visualize and analyze multi-angular data in polar and False Color Composite (FCC) forms. PolarBRDF also includes functionalities for computing important multi-angular reflectance/albedo parameters including spectral albedo, principal plane reflectance and spectral reflectance slope. Application of PolarBRDF is demonstrated using various case studies obtained from airborne multi-angular remote sensing measurements using NASA's Cloud Absorption Radiometer (CAR). Our visualization program also provides functionalities for untangling complex surface/atmosphere features embedded in pixel-based remote sensing measurements, such as the FCC imagery generation of BRDF measurements of grasslands in the presence of wildfire smoke and clouds. Furthermore, PolarBRDF also provides quantitative information of the angular distribution of scattered surface/atmosphere radiation, in the form of relevant BRDF variables such as sunglint, hotspot and scattering statistics. (C) 2016 Elsevier Ltd. All rights reserved

Radiative characteristics of clouds embedded in smoke derived from airborne multiangular measurements

Clouds in the presence of absorbing aerosols result in their apparent darkening, observed at the top of atmosphere (TOA), which is associated with the radiative effects of aerosol absorption. Owing to the large radiative effect and potential impacts on regional climate, above-cloud aerosols have recently been characterized in multiple satellite-based studies. While satellite data are particularly useful in showing the radiative impact of above-cloud aerosols at the TOA, recent literature indicates large uncertainties in satellite retrievals of above-cloud aerosol optical depth (AOD) and single scattering albedo (SSA), which are among the most important parameters in the assessment of associated radiative effects. In this study, we analyze radiative characteristics of clouds in the presence of wildfire smoke using airborne data primarily from NASA's Cloud Absorption Radiometer, collected during the Arctic Research of the Composition of the Troposphere from Aircraft and Satellites campaign in Canada during the 2008 summer season. We found a strong positive reflectance (R) gradient in the UV-visible (VIS)-near infrared (NIR) spectrum for clouds embedded in dense smoke, as opposed to an (expected) negative gradient for cloud-free smoke and a flat spectrum for smoke-free cloud cover. Several cases of clouds embedded in thick smoke were found, when the aircraft made circular/spiral measurements, which not only allowed the complete characterization of angular distribution of smoke scattering but also provided the vertical distribution of smoke and clouds (within 0.5-5km). Specifically, the largest darkening by smoke was found in the UV/VIS, with R-0.34m reducing to 0.2 (or 20%), in contrast to 0.8 at NIR wavelengths (e.g., 1.27 mu m). The observed darkening is associated with large AODs (0.5-3.0) and moderately low SSA (0.85-0.93 at 0.53 mu m), resulting in a significantly large instantaneous aerosol forcing efficiency of 25447Wm(-2-1). Our observations of smoke-cloud radiative interactions were found to be physically consistent with theoretical plane-parallel 1-D and Monte Carlo 3-D radiative transfer calculations, capturing the observed gradient across UV-VIS-NIR. Results from this study offer insights into aerosol-cloud radiative interactions and may help in better constraining satellite retrieval algorithms