A case study of air quality above an urban roof top vegetable farm.

The effect of elevation and rooftop configuration on local air quality was investigated at the Brooklyn Grange rooftop farm during a short-term observational campaign. Using multiple particle counters and sonic anemometers deployed along vertical gradients, we found that PM2.5 concentration decayed with height above the street. Samples adjacent to the street had the highest average PM2.5 concentration and frequent stochastic spikes above background. Rooftop observations 26 m above ground showed 7-33% reductions in average PM2.5 concentration compared with the curbside and had far fewer spikes. A relationship between the vertical extinction rate of PM2.5 and atmospheric stability was found whereby less unstable atmosphere and greater wind shear led to greater PM2.5 extinction due to damped vertical motion of air.

Quantifying the effect of vegetation on near-road air quality using brief campaigns.

Many reports of trees' impacts on urban air quality neglect pattern and process at the landscape scale. Here, we describe brief campaigns to quantify the effect of trees on the dispersion of airborne particulates using high time resolution measurements along short transects away from roads. Campaigns near major highways in Queens, NY showed frequent, stochastic spikes in PM2.5. The polydisperse PM2.5 class poorly represented the behavior of discrete classes. A transect across a lawn with trees had fewer spikes in PM2.5 concentration but decreased more gradually than a transect crossing a treeless lawn. This coincided with decreased Turbulence Kinetic Energy downwind of trees, indicating recirculation, longer residence times and decreased dispersion. Simply planting trees can increase local pollution concentrations, which is a special concern if the intent is to protect vulnerable populations. Emphasizing deposition to leaf surfaces obscures the dominant impact of aerodynamics on local concentration.

Spectral target-detecting system using sine-wave modulation.

Target detection is one of the key technology of precision chemical application. Previously the digital coding modulation technique was commonly used to emit and receive the optical signal in the target detection systems previously in China. It was difficult to adjust the output power, and the anti-interference ability was weak in these systems. In order to resolve these problems, the target detection method based on analog sine-wave modulation was studied. The spectral detecting system was set up in the aspects of working principle, electric circuit, and optical path. Lab testing was performed. The results showed that the reflected signal from the target varied inversely with detection distances. It indicated that it was feasible to establish the target detection system using analog sine-wave modulation technology. Furthermore, quantitative measurement of the reflected optical signal for near-infrared and visible light could be achieved by using this system. The research laid the foundation for the future development of the corresponding instrument.