Aerosol optical and physical properties during winter monsoon pollution transport in an urban environment

Source apportionment of fine aerosol particles of water-soluble and carbonaceous species measured in semi-urban (Kharagpur) and megacity (Kolkata) atmospheres over the eastern Indo-Gangetic plain: Chemical characterisation, relative abundance and anthropogenic contributions

We conducted the source apportionment of fine aerosol particles (aerodynamic diameter ≤1.6μm) collected with the indigenously designed-fabricated submicron aerosol sampler (SAS) in the eastern Indo-Gangetic plain (IGP) semi-urban (Kharagpur, KGP) and megacity (Kolkata, KOL) atmospheres, examining the chemical characteristics at KGP (January 2015-February 2016), and accentuating their abundance and the sources of anthropogenic pollution relative to KOL. The fine water-soluble inorganic ions (WSII) at KGP predominantly constituted Ca2+ (52 %) and equivalent amounts (12 % each) of Cl-, Mg2+ and secondary inorganic aerosols (sum of SO42-, NO3- and NH4+). The annual mean of SO42- at KGP was twice (thrice) larger than NO3- (NH4+); this of organic carbon (OC) was thrice elemental carbon (EC), with secondary OC being 37 % of the total OC. The concordance in peaks of OC with K+ concentrations was identified during the seasonal open biomass burning at KGP (November and May). While the annual mean of OC (EC) concentration at KGP was slightly lower than (nearly equivalent to) KOL; K+, NO3-, NH4+ and F- concentrations at KOL were twice larger than KGP. Source quantification using Positive Matrix Factorization (PMF) revealed the regional dust with crustal elements marked as clean (polluted) at KGP (KOL) constituted the largest fractional contribution among the six identified factors at both KGP and KOL. The combustion-derived anthropogenic pollution comprising about 60 % (50 %) of fine particles at KOL (KGP) was predominantly from the transportation sector (in vehicular emissions and regional dust), coal combustion (industries) and open biomass burning at KOL; it was from brick kilns, residential biofuel combustion, and open biomass burning at KGP. The source-wide distribution of measured aerosol species showed their emergence from largely different sources at KGP and KOL; thereby suggesting a prioritised strategy for sustainable emissions mitigation considering the prominent sources of combustion-derived anthropogenic pollution and aerosol species for megacity and semi-urban atmospheres.

Real-Time Synchronous 3-D Detection of Air Pollution and Wind Using a Solo Coherent Doppler Wind Lidar

The monitoring and tracking of urban air pollution is a challenging environmental issue. The approach of synchronous 3-D detection of wind and pollution using a solo coherent Doppler wind lidar (CDWL) is developed and demonstrated. The 3-D distribution of pollutant is depicted by the backscatter coefficient based on signal intensity of CDWL. Then, a high-resolution wind field is derived to track the local air pollution source with its diffusion and to analyze transboundary air pollution episodes. The approach is experimentally implemented in a chemical industry park. Smoke plumes caused by point source pollutions are captured well using plan position indicator (PPI) scanning with low elevation. A typical source of pollution is located, combining the trajectory of the smoke plume and the horizontal wind vector. In addition, transboundary air pollution caused by the transport of dust storms is detected in a vertical profile scanning pattern, which is consistent with the results of national monitoring stations and backward trajectory models. Our present work provides a significant 3-D detection approach to air pollution monitoring with its sources, paths, and heights by using a solo-CDWL system.

Association of COVID-19 pandemic with meteorological parameters over Singapore

Meteorological parameters are the critical factors affecting the transmission of infectious diseases such as Middle East Respiratory Syndrome (MERS), Severe Acute Respiratory Syndrome (SARS), and influenza. Consequently, infectious disease incidence rates are likely to be influenced by the weather change. This study investigates the role of Singapore's hot tropical weather in COVID-19 transmission by exploring the association between meteorological parameters and the COVID-19 pandemic cases in Singapore. This study uses the secondary data of COVID-19 daily cases from the webpage of Ministry of Health (MOH), Singapore. Spearman and Kendall rank correlation tests were used to investigate the correlation between COVID-19 and meteorological parameters. Temperature, dew point, relative humidity, absolute humidity, and water vapor showed positive significant correlation with COVID-19 pandemic. These results will help the epidemiologists to understand the behavior of Severe Acute Respiratory Syndrome Coronavirus 2 (SARS-CoV-2) virus against meteorological variables. This study finding would be also a useful supplement to help the local healthcare policymakers, Center for Disease Control (CDC), and the World Health Organization (WHO) in the process of strategy making to combat COVID-19 in Singapore.

Influence of the origin of the air mass on the background levels of atmospheric particulate matter and secondary inorganic compounds in the Madrid air basin

This study has assessed the influence of the origin of air mass on levels of particulate matter (PM₁₀) and chemical composition (SO₄^2- and NO₃^-) in the air basin of Madrid. A data set of back-trajectories of air mass arriving to this area of study from 15 June 15 2009 to 8 July 2011 has been analyzed. Firstly, the cluster analysis statistical method has been used to group the back-trajectories into 5 sets according to the angle, direction, and speed of the air mass. Afterwards, the synoptic meteorological scenarios associated with each cluster were obtained and interpreted. Subsequently, an analysis was made on the influence of these clusters on the surface levels of particulate pollutants recorded in a regional background station ("El Atazar"), as well as in two urban background stations ("Casa de Campo" and "CIEMAT"). Finally, potential source areas of PM₁₀, SO₄^2-, and NO₃^- that contributed to the increase in their background levels in the Madrid air basin were detected by analyzing residence times of trajectories. Transport of mineral desert dust is probably the main cause of the increase of regional and urban background levels of PM₁₀ in the Madrid air basin. In the case of SO₄^2-, relatively high levels were registered, associated with air mass coming from Southern Europe and the Mediterranean Sea. In these regions, strong emissions of SO₄^2- are produced due to industrial combustion and maritime traffic. Otherwise, relatively high levels of NO₃^- were registered during meteorological situations defined by a low baric gradient in the Iberian Peninsula. This meteorological pattern favors the accumulation of emissions from local and regional sources. Besides, the main urban centers of northeastern Europe and industrial areas located in the north African coast were also identified as potential source areas of NO₃^-. The statistical analysis of the back-trajectories by different methods and the comparison of the results obtained with observational data confirmed that numerous industrial areas in Europe and North Africa, as well as natural ones, such as deserts, had an influence on the regional and urban background levels of mass and chemical composition of particulate matter in the Madrid air basin, under the development of specific synoptic meteorological situations. Graphical abstract.

Radiative response of biomass-burning aerosols over an urban atmosphere in northern peninsular Southeast Asia

A large concentration of finer particulate matter (PM_2.5), the primary air-quality concern in northern peninsular Southeast Asia (PSEA), is believed to be closely related to large amounts of biomass burning (BB) particularly in the dry season. In order to quantitatively estimate the contributions of BB to aerosol radiative effects, we thoroughly investigated the physical, chemical, and optical properties of BB aerosols through the integration of ground-based measurements, satellite retrievals, and modelling tools during the Seven South East Asian Studies/Biomass-burning Aerosols & Stratocumulus Environment: Lifecycles & Interactions Experiment (7-SEAS/BASELInE) campaign in 2014. Clusters were made on the basis of measured BB tracers (Levoglucosan, nss-K⁺, and NO₃^-) to classify the degree of influence from BB over an urban atmosphere, viz., Chiang Mai (18.795°N, 98.957°E, 354m.s.l.), Thailand in northern PSEA. Cluster-wise contributions of BB to PM_2.5, organic carbon, and elemental carbon were found to be 54-79%, 42-79%, and 39-77%, respectively. Moreover, the cluster-wise aerosol optical index (aerosol optical depth at 500nm≈0.98-2.45), absorption (single scattering albedo ≈0.87-0.85; absorption aerosol optical depth ≈0.15-0.38 at 440nm; absorption Ångström exponent ≈1.43-1.57), and radiative impacts (atmospheric heating rate ≈1.4-3.6Kd^-1) displayed consistency with the degree of BB. PM_2.5 during Extreme BB (EBB) was ≈4 times higher than during Low BB (LBB), whereas this factor was ≈2.5 for the magnitude of radiative effects. Severe haze (visibility≈4km) due to substantial BB loadings (BB to PM_2.5≈79%) with favorable meteorology can significantly impact the local-to-regional air quality and the, daily life of local inhabitants as well as become a respiratory health threat. Additionally, such enhancements in atmospheric heating could potentially influence the regional hydrological cycle and crop productivity over Chiang Mai in northern PSEA.

Discerning the pre-monsoon urban atmosphere aerosol characteristic and its potential source type remotely sensed by AERONET over the Bengal Gangetic plain

In the present study, we evaluated the pre-monsoon urban atmosphere (UA) aerosol characteristics remotely sensed by Aerosol Robotic Network (AERONET) over the Bengal Gangetic plain (BGP) at Kolkata (KOL) and their implication in potential source types and spatiotemporal features. About 70% of the AERONET-sensed aerosol optical depth at 0.50 μ m, AOD_0.5 (Angstrom exponent, α at 0.44-0.87 μ m) during the pre-monsoon period (February to June) was greater than 0.50 (≤ 1); the pre-monsoon mean of AOD_0.5 (α) was 0.73 (0.83) which was found being slightly higher (lower) than nearby AERONET stations (Dhaka/Bhola) located over the eastern Ganges basin. The volume geometric mean radius for the fine mode (FM) (coarse mode, CM) UA aerosol from AERONET retrievals was estimated to be 0.14-0.17 (2.24-2.75) μ m. The spectral distribution of the monthly mean of UA aerosol single-scattering albedo (SSA) exhibited an increasing trend with an increase in wavelength throughout all wavelengths during April, unlike the rest of the pre-monsoon months. Investigation of aerosol types indicated the pre-dominance of dust during April and a mixture of urban/open burning with mixed desert dust during the rest of the pre-monsoon months. Potential aerosol source fields were identified over the Indo-Gangetic Plain (IGP), east coast, northwestern India, and oceanic regions; these were estimated at elevated layers of atmosphere during April and May but that at surface layers during February and June. Comparison of aerosol characteristics over the BGP (at Kolkata, KOL) with that at six other coincident AERONET sites over India revealed mean AOD at KOL being 11 to 91% higher than the rest of the AERONET stations, with the relative increase at KOL being the highest during March; this was attributed to persistent high values of both FM and CM AOD unlike the rest of the stations. The monthly mean of SSA was the lowest at KOL among AERONET stations, during February and March. Comparison of the AOD from the AERONET aerosol retrievals over the BGP UA with the coincident Moderate Resolution Imaging Spectroradiometer (MODIS) latest retrievals (C005 and C006) indicated a moderate correlation between the two retrievals; discrepancy in MODIS-retrieved relative distribution of FM and CM AOD was inferred compared to AERONET in the UA.

Contribution of biogenic and photochemical sources to ambient VOCs during winter to summer transition at a semi-arid urban site in India

This paper presents the sources and characteristics of ambient volatile organic compounds (VOCs) measured using PTR-TOF-MS instrument in a metropolitan city of India during winter to summer transition period. Mixing ratios of VOCs exhibited strong diurnal, day-to-day and episodic variations. Methanol was the most dominant species with monthly mean values of 18-22 pbbv. The emission ratios of VOCs relative to benzene calculated from nighttime data were used to estimate the relative contributions of vehicle exhaust and other sources. The increasing daytime ratios of oxygenated-VOCs (OVOCs)/benzene and isoprene/benzene from February to March indicates increasing contribution of photo-oxidation and biogenic sources. Daytime fractions of acetone (18%), acetaldehyde (15%) and isoprene (4.5%) to the sum of measured VOCs in March were higher than those in February. Variations of VOCs at lower temperatures (<25 °C) were predominantly controlled by anthropogenic sources. At high temperatures, particularly in the range of 32-40 °C during March, levels of OVOCs and isoprene were influenced by biogenic emissions. The emissions of OVOCs from vehicle exhaust were estimated to be smaller (20-40%) than those from other sources. The contributions of biogenic and secondary sources to OVOCs and isoprene increased by 10-15% from winter to summer. This study provides evidence that the winter-to-summer transition has an impact on sources and composition of VOCs in tropical urban areas.