Integration of low-cost air quality sensors with the internet of things (IoT) has become a feasible approach towards the development of smart cities. Several studies have assessed the performance of low-cost air quality sensors by comparing their measurements with reference instruments. We examined the performance of a low-cost IoT particulate matter (PM 10 and PM 2.5 ) sensor in the urban environment of Santiago, Chile. The prototype was assembled from a PM 10 -PM 2.5 sensor (SDS011), a temperature and relative humidity sensor (BME280) and an IoT board (ESP8266/ Node MCU). Field tests were conducted at three regulatory monitoring stations during the 2018 austral winter and spring seasons. The sensors at each site were operated in parallel with continuous reference air quality monitors (BAM 1020 and TEOM 1400) and a filterbased sampler (Partisol 2000i). Variability between sensor units (n = 7) and the correlation between the sensor and reference instruments were examined. Moderate inter-unit variability was observed between sensors for PM 2.5 (normalized root-mean-square error 9-24%) and PM 10 (10-37%). The correlations between the 1-h average concentrations reported by the sensors and continuous monitors were higher for PM 2.5 (R 2 0.47-0.86) than PM 10 (0.24-0.56). The correlations (R 2 ) between the 24-h PM 2.5 averages from the sensors and reference instruments were 0.63-0.87 for continuous monitoring and 0.69-0.93 for filter-based samplers. Correlation analysis revealed that sensors tended to overestimate PM concentrations in high relative humidity (RH > 75%) and underestimate when RH was below 50%. Overall, the prototype evaluated exhibited adequate performance and may be potentially suitable for monitoring daily PM 2.5 averages after correcting for RH.

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The aim of the study was to determine the mass, black carbon (BC), and elemental concentrations in fine particles (PM 2.5 ) and their variations at two sites in Ouagadougou, the capital city of Burkina Faso. The weather situation in Ouagadougou during the field campaign was dominated by high pressure with variable cloudiness and no precipitation. Diurnal temperatures varied between 19 and 38 • C and relative humidity between 10 and 60%. Winds in Ouagadougou were generally coming in from the north, showing a diurnal pattern with gusts of up to 6 m/s during daytime, while evenings and nights were calmer with very stable atmospheric conditions. However, during part of this field campaign, a period of nighttime moderately stable atmospheric conditions occurred with increased wind speed and more easterly winds. Cyclones were used for the PM 2.5 particle collection at both sites. The elemental analysis was done using energy dispersive x-ray fluorescence (EDXRF) spectroscopy. Cl, K, Ca, Ti, Mn, Fe, Cu, Zn, Br, Rb, Sr, and Pb were identified and quantified in most of the samples. The particle mass concentration was 27-164 µg/m 3 while BC varied between 1.3 and 8.2 µg/m 3 . No influence of leaded gasoline was found. Soil dust was identified as a major component of the particles, which was confirmed by comparing with the elements in a soil sample. A significant difference in elemental, BC, and mass concentrations was seen between periods with very stable and moderately stable atmospheric conditions.

Intra-urban cooling in the city of Ouagadougou, capital of Burkina Faso in the Sahel zone of West Africa, was studied during the dry seasons in 2003, 2004 and 2007. The aim was to see how vegetation, built structure and position within the built-up area influenced the nocturnal cooling. Cooling was divided into two phases. In Phase 1 (16 : 00-20 : 00 hours LST = CET), cooling was very different between the sites while in Phase 2 (20 : 00-06 : 00 hours LST), cooling rates differed insignificantly and the whole area cooled almost at the same rate. Thus the temperature differences between the sites developed during these few hours in Phase 1 were preserved during the rest of the night. In Phase 1, Evening Evapotranspirative Cooling was intensive at vegetated sites that cooled almost twice as fast as sparsely vegetated. This was indicated by a humidity rate (increase of specific humidity per hour) that was high at a vegetated site, but considerably lower at a sparsely vegetated. In Phase 2 the humidity rate was slightly negative with little difference between the sites. After a division in vegetated and sparsely vegetated sites built structure (sky view factor) were shown to influence cooling, but no influence of the position within the built-up area was traced. Thus, the site-specific properties dominated cooling, giving large intra-urban temperature differences. The study also showed the importance of considering a large enough source area to account for micro-scale advection.

ABSTRACT:Relatively little is known about the urban climate processes of the fastest growing cities in the world today. Described in this paper are urban-rural and intra-urban variations in air temperature and humidity in one of these cities; Ouagadougou, Burkina Faso. Measurements were collected from car traverses and fixed site measurements during two field studies. The aim of the study was to determine the influence of land use on the urban climate in this hot-dry region, with a focus on the role of vegetation and of a large centrally located reservoir.Analyses of results show that vegetation is the most important factor in the nocturnal urban climate in Ouagadougou, while effects of built up and paved areas are limited. Average urban-rural temperature differences demonstrate that while the evening urban heat island (UHI) reached only 1.9°C, the cool island in a densely vegetated area was 5.0°C cooler than the dry rural reference. Temperature differences of the same magnitude persisted throughout the night between vegetated and non-vegetated areas, regardless of urban or rural setting. Cooling from the open water of the reservoir was the most important parameter during daytime, while during evenings and nights, direct effects of the open water of the reservoir are very limited, and the availability of water, allowing enhanced vegetation cover, is of much greater importance compared to the water itself.The results presented here show that the urban land cover, together with climatic region, can create significant differences in the physical properties driving the urban climate in a dry-tropical city compared to those commonly found in temperate cities.