Ambient air quality of Islamabad, Pakistan, reveals that annual average mass concentration of particulate matter (PM 2.5 ) (∼45 to ∼95 μg m −3 ) and nitric oxide (NO) (∼41 to ∼120 μg m −3 ) exceeds the Pakistan's National Environmental Quality Standards (NEQS). The annual ozone (O 3 ) concentration is within the permissible limits; however, some of the hourly concentration exceeds the NEQS mostly during the summer months. Correlation studies suggest that carbon monoxide (CO) has a significant (p-value ≤ 0.01) positive correlation with NO and NO y ′ ; whereas, with O 3 , a significant (p-value ≤ 0.01) negative correlation is observed. The regression analysis estimates the background CO concentration to be ∼300 to ∼600 ppbv in Islamabad. The higher ratio of CO/NO (∼10) suggests that mobile sources are the major contributor to NO concentration. On the other hand, the ratio analysis of sulfur dioxide (SO 2 )/NO for Islamabad (∼0.011) indicates that the point sources are contributing to SO 2 in the city. NO and SO 2 correlation indicates contribution of direct sulfur emission sources. Ratios of [CO] to [NO] and [SO 2 ] to [NO], based on ambient air quality measurements, provide a test for emission inventories. The ratios of these pollutants in the available Islamabad emission inventories are consistent with ambient values for these pollutants. The correlation of PM 2.5 and NO suggests that a fraction of secondary PM 2.5 is produced by chemical conversion of NO into nitrates. The regional background O 3 concentration for Islamabad has been determined to be ∼31 ppbv. This study suggests that there is an increase in O 3 concentration with increases in photochemical conversion of NO to reservoir NO y ′ species.
A key research subject in the area of unmanned aerial vehicles (UAVs) is how to make them autonomous. Towards this goal, the most vital step is stabilizing the attitude of the vehicles. This paper presents the design of an autonomous control system for a hybrid UAV to enable it to carry out a stable hovering mission under external wind disturbances. The hovering capability of the hybrid UAV under windy conditions is analysed with computational fluid dynamics (CFD) and a control law is designed to stabilize the craft in the hovering position. The proposed hovering controller is verified with simulations and experiments. Finally, the flight control system is installed in a small prototype and a full transition flight test, including vertical take-off, transition from vertical flight to cruise, cruise, transition cruise to vertical mode and hover landing, is successfully accomplished.
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