Black carbon over a high altitude Central Himalayan Glacier: Variability, transport, and radiative impacts.

Ambient equivalent black carbon (BC) measurements spanning from June to October have been carried out over an adjoining location of Satopanth and Bhagirath-Kharak Glaciers (3858m, amsl) of Central Himalaya during the year 2019. Hourly BC varied from 12 ng m-3 to 439 ng m-3 during the entire period of observation. Monthly averaged BC values showed the highest concentration during June (230.96 ± 85.46 ng m-3) and the lowest in August (118.02 ± 71.63 ng m-3). The decrease in BC during monsoon months is attributed to limited long-range transport and rapid wet scavenging processes. Transport model studies indicate a higher retention time of tracer in Uttarakhand, Punjab, Haryana, and adjacent polluted valley regions with increased biomass burning (BB) incidences. The high rate of BC influx during June, September, and October was attributed to transport from the polluted Indo-Gangetic Plain (IGP) region, wildfires, and vehicular emissions in the valley region. Higher equivalent brown carbon (BrC) influx is linked to BB, especially wood-burning, during intense forest fires at slopes of mountains. Data obtained from limited BC observations during the 2011-19 period showed no significant BC influx change during post-monsoon. The strong correlation between BC mass and BB affirms the dominant role of BB in contributing BC to the Glacier region. Increased TOA forcing induced by surface darkening and BC atmospheric radiative heating indicate an additional warming and possible changes of the natural snow cycle over the glacier depending on the characteristics and extent of debris cover.

On the varied emission fingerprints of particulate matter over typical locations of NCR (Delhi) - A perspective for mitigation plans.

Source apportionment study of PM2.5 using positive matrix factorization was performed to identify the emission characteristic from different sectors (sub-urban residential, industrial and rapidly urbanizing) of Delhi during winter. Chemical characterization of PM2.5 included metals (Ca, Cd, Cr, Cu, Fe, K, Mg, Mn, Na, Ni, Pb and Zn), water soluble ionic compounds (WSICs) (Cl-, NO3-, SO42- and NH4+) and Carbon partitions (OC, EC). Particulates (PM2.5) were collected on filter twice daily for stable and unstable atmospheric conditions, at the locations with specific characteristics, viz. Ayanagar, Noida and Okhla. Ions solely occupied 50% of the total PM2.5 concentration. Irrespective of location, high correlation between OC and EC (0.871-0.891) at p ≤ 0.1 is observed. Relatively lower ratio of NO3/SO4 at Ayanagar (0.696) and Okhla (0.84) denotes predominance of emission from stationary sources rather than mobile sources like that observed at Noida (1.038). Using EPA PMF5.0, optimum factors for each location are fixed based on error estimation (EE). Crustal dust, vehicular emission, biomass burning and secondary aerosol are the major contributing sources in all the three locations. Incineration contributes about 19% at Ayanagar and 18% at Okhla. Metal industries in Okhla contribute about 19% to PM2.5. These specific local emissions with considerable potency are to be targeted for long-term policymaking. Considerable secondary aerosol contribution (15%-24%) indicates that gaseous emissions also need to be reduced to improve air quality.

Variability of ozone and oxides of nitrogen in the tropical city, Bengaluru, India.

Bengaluru, also considered India's Silicon Valley, has seen steady growth in population over the years. Bengaluru's rapid development has resulted in dwindling reservoirs, increased traffic congestion, high levels of air pollution, and, to some measure, a rise in summer temperatures. As a result of these changes in urban form over the last decade, anthropogenic heat fluxes for ozone production have increased. However, an observational study on the effects of growing urbanisation on trace gases in Bengaluru for various seasons and periods of the day is missing. Hence, in situ measurements of O3, NO, NO2, and NOX concentrations were carried out at Bengaluru, India, from January 2015 to December 2018. The data were examined for diurnal and interannual variations in trace gas mixing concentrations. The diurnal trend in O3 exhibits unimodal behaviour. Changes in photochemistry, local meteorology, and the planetary boundary layer's distinctive features cause a rise in the value of concentrations and lead to a peak. In contrast, the diurnal trend in NO, NO2, and NOX displayed a bimodal peak due to the combined effect of vehicular emissions and the planetary boundary layer. The link involving the oxidant OX (O3 + NO2) and NOx levels were investigated to determine the NOx-independent regional and NOx-dependent local contributions to OX in the atmosphere. Daytime contributions are higher than night-time contributions, according to the present study. The observed anomalies could be the consequence of photochemical processes that produce OX.

Assessments of population exposure to environmental pollutants using air quality measurements during Commonwealth Games-2010.

During the "Commonwealth Games" 2010 (CWG-2010) in Delhi, the Indian government has implemented an ambitious project "System of Air quality Forecasting And Research (SAFAR)" for monitoring and forecasting air-quality scenario. Using high-precision spatio-temporal measurements of criteria pollutants from the SAFAR network, the number of cases are estimated for total, cardiovascular and respiratory mortalities and hospital admissions. In a thinly populated airport area, the excess number of cases for total mortality show ∼10 for PM2.5 and 25 for PM10, whereas, ∼110 for PM2.5 and ∼300 for PM10 in most populous Delhi University (DU) area. Cardiovascular mortality in airport area show ∼5 and <10 for PM2.5 and PM10, respectively, but, in DU area show ∼55 for PM2.5 and ∼140 for PM10. In DU locality, respiratory mortality shows ∼7 and ∼20 for PM2.5 and PM10 and, hospital admissions show ∼11 and ∼30 for PM2.5 and PM10, respectively. In airport area, excess cases of respiratory mortality and hospital admission tends to one for exposure to PM2.5 or PM10 levels indicating effective exposure is the key factor for health hazards. As public health gains, low air pollution levels were observed before the CWG due to effective washout by monsoonal rain and during CWG under policy-induced air quality measures could increase the life expectancy as against to post-CWG period. These results are important for the megacities in developing world as the SAFAR project is internationally recognized by the Global Urban Research Meteorology and Environment of the World Meteorological Organization.

Anomalous behaviour of ozone under COVID-19 and explicit diagnosis of O3-NOx-VOCs mechanism.

Air pollution is linked to higher rates of human mortality especially those infected with COVID 19. Ozone is a harmful pollutant and is responsible for many health issues. However, some reports suggest that ozone is a strong disinfectant, and can kill the viruses. We hereby, report on the vulnerability of ozone due to COVID-19 lockdown whose levels flutter from surging to saturation in a highly polluted Indian capital, due to significant decline in anthropogenic emissions of ozone precursors. Average observed levels stabilized at 30 ppb, 12 ppb, 740 ppb, and 900 ppb for ozone (O3), nitrogen dioxide (NO2), carbon monoxide (CO) and volatile organic compounds (VOCs) respectively during lockdown period from 27th March to 10th April 2020. The NO2, CO and VOC declined by 50 %, 37 %, 38 % respectively during the lockdown period of 2020 as compared to similar period in 2019. The anomalous response of ozone during the lockdown is explained by resolving the poorly known complex O3-NOx-VOCs mechanism with the help of data from air monitoring stations in Delhi, India. The data obtained from this study advances the fundamental understanding of ozone chemistry that may lead to improved ozone parameterization in chemical transport models and better planning of ozone risk management strategies for any global mega cities.

Black carbon over a central Himalayan Glacier (Satopanth): Pathways and direct radiative impacts.

Continuous measurement of Black Carbon (BC) concentration was carried out during May-October 2018 periods over Satopanth Glacier in the central Himalayas. BC concentrations varied between 28 and 287 ngm-3 on different days during the observational period. High concentration of BC was observed in the month of May (monthly mean of 221 ± 79 ngm-3), and a lower concentration was observed in August (monthly mean of 92 ± 58 ngm-3). Biomass burning was found to contribute up to 58% of BC mass over the region, with lower contribution during June and higher during the month of May. Compensation parameter (K) values were found to vary between -0.005 and 0.005 in different months, asserting the presence of aged BC in June to October months and relatively fresh BC in the month of May. Concentration weighted trajectory (CWT) analysis showed that the air mass from Indo Gangetic Plains (IGP) was responsible for the majority of transported BC in July & August months (up to 65%) and partially in September (up to 40%). However, the transport from Middle East and far north-western regions was found to be the major contributor to BC concentrations in other months. The estimated BC direct radiative forcing was found to induce 4.5 to 7.6 Wm-2 reduction of radiation at the surface (SFC) and the forcing was +2.3 to +3.5 Wm-2 at the Top of the Atmosphere (TOA). The BC induced atmospheric heating rates were found to be up to 0.35 k day-1 over the region. The sensitivity of snow albedo to radiative forcing was studied, and it is found that BC albedo changes tend to decrease albedo with an increase in BC-snow deposition, leading to a decrease in atmospheric absorption.

Performance of high resolution (400 m) PM2.5 forecast over Delhi.

This study reports a very high-resolution (400 m grid-spacing) operational air quality forecasting system developed to alert residents of Delhi and the National Capital Region (NCR) about forthcoming acute air pollution episodes. Such a high-resolution system has been developed for the first time and is evaluated during October 2019-February 2020. The system assimilates near real-time aerosol observations from in situ and space-borne platform in the Weather Research and Forecasting model coupled with Chemistry (WRF-Chem) to produce a 72-h forecast daily in a dynamical downscaling framework. The assimilation of aerosol optical depth and surface PM2.5 observations improves the initial condition for surface PM2.5 by about 45 µg/m3 (about 50%).The accuracy of the forecast degrades slightly with lead time as mean bias increase from + 2.5 µg/m3 on the first day to - 17 µg/m3 on the third day of forecast. Our forecast is found to be very skillful both for PM2.5 concentration and unhealthy/ very unhealthy air quality index categories, and has been helping the decision-makers in Delhi make informed decisions.

Seasonal progression of surface ozone and NOx concentrations over three tropical stations in North-East India.

Monitoring of surface ozone (O3) and Nitrogen Oxides (NOx) are vital for understanding the variation and exposure impact of these trace gases over the habitat. The present study analyses the in situ observations of surface O3 and NOx for January-December 2016, for the first time over three sites of North-Eastern India (Aizwal, Gauhati and Tezpur). The sites are major cities of north-eastern India, located in the foothills of Eastern Himalaya and have no industrial impacts. We have analysed the seasonal variation of O3 and NOx and found that the site Tezpur, which is in the valley area of Eastern Himalaya, is experiencing higher values of pollutants persisting for a long time compared to the other two stations. The correlation of surface O3 with the air temperature at all three sites suggested that all the O3 may not be locally produced, but has the contribution of transported pollution reaching to stations. The study also attempts to discover the existing variability in the surface O3 and NOx over the study area by employing continuous wavelet analysis.

Investigation of emission characteristics of NMVOCs over urban site of western India.

This is the first study to characterize the variation and emission of C2-C5 non-methane volatile organic compounds (NMVOCs) in a semi-urban site of western India based on measurements during February-December 2015. Anthropogenic NMVOCs show clear seasonal dependence with highest in winter and lowest in monsoon season. Biogenic NMVOCs likes isoprene show highest mixing ratios in the pre-monsoon season. The diurnal variation of NMVOC species can be described by elevated values from night till morning and lower values in the afternoon hours. The elevated levels of NMVOCs during night and early morning hours were caused mainly by weaker winds, temperature inversion and reduced chemical loss. The correlations between NMVOCs, CO and NOx indicate the dominant role of various local emission sources. Use and leakage of liquefied petroleum gas (LPG) contributed to the elevated levels of propane and butanes. Mixing ratios of ethylene, propylene, CO, NOx, etc. show predominant emissions from combustion of fuels in automobiles and industries. The Positive Matrix Factorization (PMF) source apportionments were performed for the seven major emission sectors (i.e. Vehicular exhaust, Mixed industrial emissions, Biomass/Fired brick kilns/Bio-fuel, Petrochem, LPG, Gas evaporation, Biogenic). Emissions from vehicle exhaust and industry-related sources contributed to about 19% and 40% of the NMVOCs, respectively. And the rest (41%) was attributed to the emissions from biogenic sources, LPG, gasoline evaporation and biomass burning. Diurnal and seasonal variations of NMVOCs were controlled by local emissions, meteorology, OH concentrations, long-range transport and planetary boundary layer height. This study provides a good reference for framing environmental policies to improve the air quality in western region of India.

Ambient particulate matter and carbon monoxide at an urban site of India: Influence of anthropogenic emissions and dust storms.

Continuous measurements of PM2.5, PM10 and CO were conducted at an urban site of Udaipur in India from April 2011 to March 2012. The annual mean concentrations of PM2.5, PM10 and CO were 42 ± 17 µg m-3, 114 ± 31 µg m-3 and 343 ± 136 ppbv, respectively. Concentrations of both particulate and CO showed high values during winter/pre-monsoon (dry) period and lowest in the monsoon season (wet). Local anthropogenic emission and long-range transport from open biomass burning sources along with favourable synoptic meteorology led to elevated levels of pollutants in the dry season. However, higher values of PM10/PM2.5 ratio during pre-monsoon season were caused by the episodes of dust storm. In the monsoon season, flow of cleaner air, rainfall and negligible emissions from biomass burning resulted in the lowest levels of pollutants. The concentrations of PM2.5, PM10 and CO showed highest values during morning and evening rush hours, while lowest in the afternoon hours. In winter season, reductions of PM2.5, CO and PM10 during weekends were highest of 15%, 13% and 9%, respectively. In each season, the highest PM2.5/PM10 ratio coincided with the highest concentrations of pollutants (CO and NOX) indicating predominant emissions from anthropogenic sources. Exceptionally high concentrations of PM10 during the episode of dust storm were due to transport from the Arabian Peninsula and Thar Desert. Up to ∼32% enhancements of PM10 were observed during strong dust storms. Relatively low levels of O3 and NOx during the storm periods indicate the role of heterogeneous removal.

Atmospheric transport of ozone between Southern and Eastern Asia.

This study describes the effect of pollution transport between East Asia and South Asia on tropospheric ozone (O3) using model results from the Task Force on Hemispheric Transport of Air Pollution (TF HTAP). Ensemble mean O3 concentrations are evaluated against satellite-data and ground observations of surface O3 at four stations in India. Although modeled surface O3 concentrations are 1020ppb higher than those observed, the relative magnitude of the seasonal cycle of O3 is reproduced well. Using 20% reductions in regional anthropogenic emissions, we quantify the seasonal variations in pollution transport between East Asia and South Asia. While there is only a difference of 0.05 to 0.1ppb in the magnitudes of the regional contributions from one region to the other, O3 from East Asian sources affects the most densely populated parts of South Asia while Southern Asian sources only partly affect the populated parts of East Asia. We show that emission changes over East Asia between 2000 and 2010 had a larger impact on populated parts of South Asia than vice versa. This study will help inform future decisions on emission control policy over these regions.

Evaluating population exposure to environmental pollutants during Deepavali fireworks displays using air quality measurements of the SAFAR network.

Indian government has implemented a state of art project "System of Air quality Forecasting And Research (SAFAR)" for assessing the air-quality scenario in Delhi during "Commonwealth Games-2010" which is operational in Delhi. Using a high resolution data of the SAFAR network, we estimate the excess numbers of cases for total, cardiovascular and respiratory mortalities and hospital admissions with the air-quality response to population attributable-risks due to emissions from fireworks displays (Deepavali-2010). The ratios of numbers of excess cases for fireworks displays (Deepavali) to those of non-Deepavali period (CWG-2010) vary from 1.75 to 3.5 for PM(2.5) and from 3 to 8 for PM(10) at monitoring stations in study area except in an airport. These ratios approach to 1 for PM(2.5) or PM(10) in airport area which can be attributed to restrictions on fireworks displays and eventually a very low population exposure. The numbers of excess cases for PM(2.5) and PM(10) during extreme emissions by fireworks displays are about 2-fold to those of non-Deepavali period. The SAFAR is recognized by the Global Urban Research Meteorology and Environment of the World Meteorological Organization and thus results would likely to provide episodic limits for developing countries in common line with the air-quality standards set for developed world for pollutant levels due to emissions from the fireworks displays when population of country celebrates traditional festivals collectively.

Vertical transport of ozone and CO during super cyclones in the Bay of Bengal as detected by Tropospheric Emission Spectrometer.

Vertical profiles of carbon monoxide (CO) and ozone retrieved from Tropospheric Emission Spectrometer have been analyzed during two super cyclone systems Mala and Sidr. Super cyclones Mala and Sidr traversed the Bay of Bengal (BOB) region on April 24-29, 2006 and November 12-16, 2007 respectively. The CO and ozone plume is observed as a strong enhancement of these pollutants in the upper troposphere over the BOB, indicating deep convective transport. Longitude-height cross-section of these pollutants shows vertical transport to the upper troposphere. CO mixing ratio ~90 ppb is observed near the 146-mb level during the cyclone Mala and near 316 mb during the cyclone Sidr. Ozone mixing ratio ~60-100 ppb is observed near the 316-mb level during both the cyclones. Analysis of National Centers for Environmental Prediction (NCEP) reanalysis vertical winds (omega) confirms vertical transport in the BOB.

Anomalous low tropospheric column ozone over eastern India during the severe drought event of monsoon 2002: a case study.

BACKGROUND, AIM, AND SCOPE: The present study is an attempt to examine some of the probable causes of the unusually low tropospheric column ozone observed over eastern India during the exceptional drought event in July 2002. METHOD: We examined horizontal wind and omega (vertical velocity) anomalies over the Indian region to understand the large-scale dynamical processes which prevailed in July 2002. We also examined anomalies in tropospheric carbon monoxide (CO), an important ozone precursor, and observed low CO mixing ratio in the free troposphere in 2002 over eastern India. RESULTS AND DISCUSSION: It was found that instead of a normal large-scale ascent, the air was descending in the middle and lower troposphere over a vast part of India. This configuration was apparently responsible for the less convective upwelling of precursors and likely caused less photochemical ozone formation in the free troposphere over eastern India in July 2002. CONCLUSION: The insight gained from this case study will hopefully provide a better understanding of the process controlling the distribution of the tropospheric ozone over the Indian region.

Satellite derived trends in NO2 over the major global hotspot regions during the past decade and their inter-comparison.

We assessed satellite derived tropospheric NO(2) distribution on a global scale and identified the major NO(2) hotspot regions. Combined GOME and SCIAMACHY measurements for the period 1996-2006 have been used to compute the trends over these regions. Our analysis shows that tropospheric NO(2) column amounts have increased over the newly and rapidly developing regions like China (11+/-2.6%/year), south Asia (1.76+/-1.1%/year), Middle East (2.3+/-1%/year) and South Africa (2.4+/-2.2%/year). Tropospheric NO(2) column amounts show some decrease over the eastern US (-2+/-1.5%/year) and Europe (0.9+/-2.1%/year). We found that although tropospheric NO(2) column amounts decreased over the major developed regions in the past decade, the present tropospheric NO(2) column amounts over these regions are still significantly higher than those observed over newly and rapidly developing regions (except China). Tropospheric NO(2) column amounts show some decrease over South America and Central Africa, which are major biomass burning regions in the Southern Hemisphere.