Solid or liquid particles suspended in the air (ranging from nanometer to 10-micrometer diameter) termed as aerosols are produced by several natural and anthropogenic sources (such as earth crust, desert, volcanic eruption, sea spray, fossil fuel combustions in industries, biomass and biofuel burning, vehicular traffic). During the recent past, the atmospheric aerosol productions from anthropogenic sources into the atmosphere have been tremendously increasing and have gained the impact on regional air quality, visibility degradation, cloud formation and atmospheric chemistry, radiation budget etc. and on human health too. In addition to this, the rapid increases in urbanization and industrialization have resulted in extremely poor air quality in megacities all over the world. According to various national and international studies, it was observed that the air quality over the northern part of Indian cities especially Indo-Gangetic Basin and Brahmaputra River Valley region as well as Himalayan regions have received to be the worst air quality during the post monsoon and winter periods. In addition to this, during the summer period, glacier melting over high altitude Himalayan regions was observed. In foothills of Himalayan regions, it was noticed that in some occasions, the level of mass concentrations of aerosols reaches up to 800 µg m–3 (Tiwari et al., 2016). Recently, in the mega city the Delhi, the government has declared severe levels of toxic air pollution in Delhi an “emergency situation” as administrators announce a plan to temporarily shut construction sites and a coal-fired power station to bring the situation under control and schools in the capital of India were closed for three days due to six days of heavy smog (in the month of Nov. 2016). During the pre-monsoon and winter periods, the wind/air masses passes from South West direction where several industrialized cities are located and are affecting, the lower altitude of the Himalayan region.
Atmospheric observations and model simulations of aerosol physical and optical properties, as well as radiative effects, under high and complex absorption regimes are extremely challenging. The availability of measurements with well-assessed and improved accuracy is also fundamental for model constraint and assessment. It is important to test and validate both ground-based and satellite measurement techniques as well as model simulations in “real” atmospheric conditions. This is particularly urgent for “hot-spot” regions, both in Europe and elsewhere in the world (Atmospheric Brown Clouds), where anthropogenic emissions and natural contributions strongly influence the absorbing aerosol components.
Simpler and lower cost sensors for particulate and gaseous air pollution monitoring are now spreading rapidly for non-regulatory applications. The low-cost of these sensors makes them suitable for large scale networks and accessible to the general public. The small size of these sensors also suggests applications such as monitoring by bicycles, pedestrians and even flying drones. These sensors can be the building blocks for a sensor network to map the dynamics of air quality (e.g., probing hot spots of emissions), for evaluating the exposure of air pollutants in personal scale (e.g., mobile monitoring), or improving the temporal and spatial resolution of monitoring information (e.g., vertical or 3D UAV measurements). However at present there are few standards concerning data quality. In view of the rapid pace of developments in sensor technology, the journal Aerosol and Air Quality Research (AAQR) will host a Special Issue (SI) with the theme "Low-cost Air Pollution Sensors". Papers contributed from 10th International Aerosol Conference (IAC 2018) in St. Louis and other papers relevant to low-cost and portable sensors are welcome. All accepted papers will be collected in a single volume as a special issue.