Long-term variability and source apportionment of black carbon aerosols over a high-altitude site in the Western Ghats, India

Atmospheric aerosols which serve as cloud condensation nuclei (CCN) are key elements of the hydrological cycle and climate. In the present work, aerosol–CCN variability and their relationship have been studied for the first time at Mahabaleshwar, a high altitude (1348 m AMSL) site in Western Ghats, using one year (June 2012–May 2013) of observations. Present study has been done in two sections in which first temporal variability (diurnal and seasonal) of aerosol and CCN has been analyzed. Later CCN to aerosol ratio and other microphysical properties have been investigated along with detail discussion on possible sources of aerosol. First part, i.e., diurnal variation in aerosol and CCN concentration has shown relatively higher values during early morning hours in monsoon season whereas in winter and pre-monsoon it was higher in the evening hours. Seasonal mean variation in aerosol and CCN (SS above 0.6 %) has shown higher (less) in monsoon (winter) season. Temporal variation reveals dominance of fine-mode aerosol during monsoon season over the study region. In the second part temporal variation of activation ratio, k value (exponent of CCN super-saturation spectra) and geometric mean aerosol diameter have been analyzed. Variation of activation ratio showed the ratio is higher in monsoon especially for SS 0.6–1 %. The analysis also showed high k value during monsoon season as compared to other seasons (pre-monsoon and winter) which may be due to dominance of hygroscopic aerosols in the maritime air masses from Arabian Sea and biogenic aerosol emissions from the wet forest. Analyzed mean aerosol diameter is much smaller during monsoon season with less variability compared to other seasons. Overall analysis showed that aerosol and CCN concentration was higher over this high altitude site despite of dominant sink processes such as cloud scavenging and washout mechanisms indicating local emissions and biogenic Volatile Organic Compounds (BVOC) emissions from wet forest as major sources.

Seasonal variability in chemical composition and source apportionment of sub-micron aerosol over a high altitude site in Western Ghats, India

Processes governing the surface ozone over a tropical hill station in the Western Ghats

Long-Term Variability, Meteorological Influences, Source Apportionment and Long-Range Transport of Black Carbon Aerosol at a High-Altitude Urban Centre in the Kashmir Valley, North-Western Himalaya

Droplet characteristics in monsoon clouds before rain as observed over a high altitude site in Western Ghats, India

This study presents the characteristics of black carbon aerosol (BC) over a high-altitude site, Mahabaleshwar during the monsoon season. The mass concentration of BC exhibits a morning peak and a daytime build-up with a mean mass concentration of 303 ± 142ngm-3. The simultaneous measurements of aerosol particle number concentration (PNC), cloud condensation nuclei concentration (CCN), and non-refractory particulate matter less than 1μm size (NR-PM1) were also made by using a Wide-Range Aerosol Spectrometer (WRAS), CCN counter and Aerosol Chemical Speciation Monitor (ACSM) respectively. The source apportionment using wavelength-dependent light absorption model reveals the dominance by wood burning sources during morning hours and traffic sources during remaining hours of the day. The diurnal variation of PNC follows the variability of BC mass concentration. However, CCN concentrations were high during the morning hours coinciding with the increased fractional contribution of organics. The k-means clustering coupled with fuzzy algorithm highlights the effect of different sources on aerosol size distribution. On the basis of size distribution curve, the 3 clusters were attributed to wood burning (mean diameter range: 50-100nm), traffic (30-50nm), and background aerosols (65-95nm). The combined analysis of k-means clustering, fractional contribution of organics, and kappa variation suggests that higher CCN concentration during morning is mainly attributed to probable emission of the water-soluble organic/inorganic compounds from wood burning.

Atmospheric aerosols significantly impact climate, and the hydrological cycle, in high-altitude regions like the Western Ghats in India, where monsoon dynamics play a critical role. Here we present the first Q-ACSM-based characterization of non-refractory submicron aerosol (NR-PM1) and organic aerosol (OA) source apportionment from Munnar, Kerala, during the Southwest monsoon season (06 June-25 July 2021).The organics comprised the largest fraction of NR-PM1 (42.1 ± 23.7%), closely followed by sulfate (41.0 ± 19.6%). Aerosol composition was strongly controlled by meteorological regime: sulfate dominated during active monsoon periods and exhibited a persistent high-speed W-SW transport signature consistent with strong marine influence, while organics became the dominant fraction (52%) during the mixed period.OA source apportionment, conducted using Positive Matrix Factorization (PMF), identified four key factors: hydrocarbon-like OA (HOA, 11.4 ± 10.4%), biomass-burning OA (BBOA, 14.0 ± 13.8%), Biomass-Burning-derived Oxygenated OA (BB-OOA, 40.2 ± 23.0%), and Oxygenated OA (OOA, 34.3 ± 24.3%), suggesting dominance of secondary aerosols in the region. These findings highlight the contrasting roles of long-range marine transport and local secondary processing in shaping fine aerosol composition at high-altitude monsoon sites, with implications for aerosol hygroscopicity and cloud condensation nuclei activity over the Western Ghats.

Source apportionment of black carbon aerosols in winter across China

Spatio-temporal variations of absorbing aerosols and their relationship with meteorology over four high altitude sites in glaciated region of Pakistan

Aerosol-CCN characteristics and dynamics during a pre-monsoon dust storm (April 6-11, 2015) over a high-altitude site ((17.92°N, 73.66°E, and 1348m above mean sea level (MSL)) in Western Ghats, India, has been studied using ground-based observations, satellite, and reanalysis datasets. Spatial distribution of dust surface mass concentration along with the back trajectory analysis showed the Arabian Desert area (Rub-Al-khali desert) as the source region and strong westerly winds transported the dust particles toward the Indian subcontinent. High values noticed in the surface PM10 (PM2.5), i.e., ~ 450 (~ 130) µg m-3, MODIS AOD550nm (0.6), and MERRA 2 dust surface mass concentration (5 × 10-7kgm-3) along MODIS true color images confirmed the dust storm event on April 6, 2015 over the observational site. Size-segregated aerosol number concentration measured from ground-based observations showed the dominance of Aitken, accumulation, and coarse mode particles during dust period. CCN concentrations at 0.1, 0.3, 0.5, 0.7, and 0.9% SS were analyzed. A low value of CCN concentration and activation fraction (~ 0.3) near surface was noticed during dust storm day, suggesting insoluble mineral dust particle being transported. Analyzed vertical velocity during pre-dust period showed downdraft between 900 and 750hPa, suggesting dust transport from upper altitudes toward the observational site. WRF-Chem model simulation also captured the dust storm event, and the results are in good agreement with the observation with a significance of 95% confidence level.

Clouds play a significant role in the dynamics and thermodynamics of the atmosphere. To understand the impact of clouds on climate and for better representation of these in the global models, accurate information about the temporal, spatial and vertical distribution of cloud properties such as microphysical, morphological and types are essential. In the present work, vertical structure and microphysics of clouds during southwest (SW) monsoon has been studied from a high altitude site (Mahabaleshwar (17.92°N, 73.66°E, and 1348 m above mean sea level (MSL)) and within ± 0.1 degrees) over Western Ghats, India. Vertical structure of the clouds has been detailed using radiosonde observations. Warm cloud microphysics was investigated using in-situ ground and aircraft cloud measurements. Radiosonde profiles showed the presence of single and multi-layered clouds over the observational site. Higher occurrence frequency for cloud layers below 2 km and above 6 km altitude compared to mid-level clouds (2 to 6 km) during SW monsoon were noticed. Higher occurrences of single layer clouds during June and September (transition period) were noticed whereas frequency of two-layer was higher in July and August (core period). Low (~30%) and high-level (~60%) clouds were dominantly seen compared to mid-level clouds over the observational site during SW monsoon. Warm cloud microphysics was investigated using collocated ground and airborne in situ measurements. Cloud microphysical properties such as cloud droplet number concentration (CDNC), liquid water content (LWC), droplet effective diameter (ED), droplet mean radius (Rm) respectively were analyzed. The cloud liquid water content and the effective droplet diameter showed increase with altitude. Analyzed cloud droplet size distribution (DSD) showed a steep decrease in number concentration of droplets above 25 µm diameters at altitudes above 1800 m, suggesting active collision-coalescence. This is the first such report combining in situ observations from two different platforms to study the vertical structure of monsoon clouds over a complex terrain like the Western Ghats in India.  

Growth variations of Common beech ( Fagus sylvatica L.) under different climatic and environmental conditions in Europe—a dendroecological study

Role of anthropogenic emissions and meteorology on ultrafine particle bursts over a high altitude site in Western Ghats during pre-monsoon

Black carbon (BC) aerosols are important for absorbing aerosols, affecting global climate change and regional air quality, and potentially harming human health. From March to May 2023, we investigated black carbon aerosol levels and air pollution in Beijing. Employing methods such as linear regression, Potential Source Contribution Function (PSCF) and Concentration-Weighted Trajectory (CWT), we analyzed the characteristics and sources of black carbon aerosols in the region. Results indicate that the light absorption coefficients of BC and BrC decrease with increasing wavelength, with BrC accounting for less than 40% at 370 nm. Daily variations in BC and PM2.5 concentrations exhibit similar trends, peaking in March, and BC displays a distinct bimodal hourly concentration structure during this period. Aethalometer model results suggest that liquid fuel combustion contributes significantly to black carbon (1.08 ± 0.71 μg·m−3), surpassing the contribution from solid fuel combustion (0.31 ± 0.2 μg·m−3). Furthermore, the significant positive correlation between BC and CO suggests that BC emissions in Beijing predominantly result from liquid fuel combustion. Potential source area analysis indicates that air masses of spring in Beijing mainly originate from the northwest (40.93%), while potential source areas for BC are predominantly distributed in the Beijing–Tianjin–Hebei region, as well as parts of the Shandong, Shanxi and Henan provinces. Moreover, this study reveals that dust processes during spring in Beijing have a limited impact on black carbon concentrations. This study’s findings support controlling pollution in Beijing and improving regional air quality.

Aerosol composition and source apportionment in Santiago de Chile