Performance evaluation of light weight gas sensor system suitable for airborne applications against co-location gas analysers over Delhi.

In the present work, we discuss the light-weight gas sensor system (LWGSS) [350 g, 7″ ∗ 3″] originally developed at CSIR-National Physical Laboratory. This instrument is equipped with low-cost electrolytic gas sensors for quantifying major gaseous pollutants present in the atmosphere. Alphasense electrochemical gas sensors were used to measure gas pollutant species such as CO, SO2, NO2, O3 and H2S. In our experiment, we focus on the observation of CO, SO2, NO2, O3 using this system. LWGSS has been designed for vertical observations using balloons or unmanned aerial vehicles (UAVs) to study the gaseous concentration in the atmospheric boundary layer (ABL). But, before using such instruments in field campaigns, there is a strong need for the inter-comparison of these instruments with that of the collocated high-end gas analysers. Thus, the inter-comparisons were performed between LWGSS and other high-end analysers during 6-7, March 2017 and 26-27, April 2017. The LWGSS system comprising all the sensors was compared against high-end analyser present at CSIR-NPL for ozone and other gas analysers present at IMD, New Delhi. The ozone sensor deployed in LWGSS showed good correlation (i.e. R2 = 0.83, slope = 0.93) against the high-end ozone gas analyser, which was calibrated with primary ozone facility (SRP43) available at CSIR-NPL. Inter-comparisons performed for NO2, SO2 and CO showed different results. While the NO2 gas sensor showed medium correlation (R2 = 0.75; slope = 0.49), the SO2 and CO gas sensor showed a poor correlation (and R2 = 0.44; slope = 0.98; R2 = 0.28, slope = 0.79) respectively, when compared with co-location gas analysers present at IMD, New Delhi. Comparisons were performed for LWGSS data during 1-28 February 2018 with data collected at CPCB station (Shadipur, Delhi) and IMD station (Pusa, Delhi). The comparison results showed variations in LWGSS CO and SO2 data whereas LWGSS O3 and NO2 results were in accordance with data collected at aforementioned monitoring stations.

How do the indoor size distributions of airborne submicron and ultrafine particles in the absence of significant indoor sources depend on outdoor distributions?

Although almost all epidemiological studies of smaller airborne particles only consider outdoor concentrations, people in Central Europe actually spend most of their time indoors. Yet indoor pollutants such as organic gases, allergens and dust are known to play a prominent role, often affecting human health more than outdoor ones. The aim of this study was to ascertain how the indoor particle size distributions of submicron and ultrafine particles correlate with the outdoor concentrations in the absence of significant indoor sources. A typical indoor particle size distribution pattern has one or two modes. In the absence of significant indoor activities such as smoking, cooking etc., outdoor particles were found to be a very important source of indoor particles. The study shows that in the absence of significant indoor sources, the number of indoor concentrations of particles in this size range are clearly lower than the outdoor concentrations. This difference is greater, the higher the number of outdoor concentrations. However, the drop in concentration is not uniform, with the decrease in concentration of smaller particles exceeding that of larger ones. By contrast, the findings with larger particle sizes (diameter > 1 microm) exhibit rather linear concentration decreases. The non-uniform drop in the number of concentrations from outdoors to indoors in our measurements considering smaller particles ( >0.01 microm) is accompanied by a shift of the concentration maxima to larger particle diameters.

Aerosol number concentrations and size distributions at mountain-rural, urban-influenced rural, and urban-background sites in Germany.

Long-term aerosol measurements have been made at three sites in Germany, representing different levels of pollution: Hohenpeissenberg (mountain-rural), Melpitz (urban-influenced rural), and Leipzig (urban background). (Urban background aerosol represents a mixture of aerosols emitted in the city and aerosols transported into the city measured at a site with no direct emissions nearby.) To provide data that will allow better estimates of the influence of environmental aerosol particles on humans, we review diurnal variations of mean total number concentrations and size distributions of submicrometer environmental aerosol particles (including ultrafine particles smaller than 100 nm) for winter and summer periods in these three regions. Number concentrations and size distributions are compared and related to peak traffic periods and to meteorologically induced new-particle formation processes. The number concentration increase with increasing level of pollution. The mountain-rural site shows the smallest and the urban background site the highest number concentration. The relative diurnal variation of the number concentration between day and night, however, is for all sites nearly the same. Generally, traffic-related number concentration during rush-hour periods peaks in the size range of 20-30 nm. Due to weaker atmospheric convective processes in winter, this traffic-related aerosol is more pronounced than that in summer. In summer, meteorologically induced new-particle formation processes add another number concentration peak to the aerosol near 10 nm. This peak occurs near noon, independent of the day of the week. For the mean number concentrations and size distribution, this new-particle formation process was only relevant for the urban-influenced rural and the urban-background sites.

Electrodynamic Trapping of Aerocolloidal Particles: Experimental and Theoretical Trapping Limits

Aerocolloidal particles have been trapped from an uncharged source aerosol using an electrodynamic balance. Graphite and soot particles were charged photoelectrically using a Xe2 (172 nm) excimer lamp, while particles of titanium dioxide, sodium nitrate, and diethylhexyl sebacate (DEHS) were charged using a unipolar corona charger prior to injection into the chamber. It was found that the Stokesian drag force produced by convection in the balance chamber can destabilize the levitated microparticle when it exceeds the electrostatic force required to center the particle. Although the electrostatic restoring force can be increased by increasing either the particle charge or the ac field strength, charging of the particles is more difficult as the particle diameter is decreased, which gives rise to a trapping limit. Monodisperse DEHS particles were used to determine the experimental trapping limit for unipolar charging. For the experimental apparatus used in this study, a diameter of about 1 µm was found to be the trapping limit for DEHS. Results are compared to the theoretical trapping limit calculated by a force balance on a particle exposed to motion of the surrounding gas.