Other Insights

The Impact of Aerosols on the Environment

We recently sat down with Professor S.K. Satheesh to discuss his work on the impact of aerosols on the environment. S.K. Satheesh is a professor at the Centre for Atmospheric and Oceanic Sciences, Indian Institute of Science, and the director of the Divecha Centre for Climate Change. He is the executive director of the South Asia regional office of the Future Earth initiative and editor of Current Science.

He was awarded the Infosys Prize in physical sciences in 2018 for his pioneering scientific work in the field of climate change. His studies on black carbon (BC) aerosols have helped scientists understand the impact of these particles on climate, precipitation and human health across the Indian subcontinent.

Here are a few excerpts from our conversation with Professor Satheesh:

1. Can you tell us a little bit about your research on the impact of black carbon aerosol particles? What does it mean for the environment, industry and society at large?

In the past several decades, scientists have pursued the science of aerosols and their impact on the environment. As an example, we have undertaken numerous field experiments over the Indian landmass and remote oceanic regions using research ships and instrumented aircraft in addition to a network of ground-based observatories. We’ve found strong meridional gradients in elevated aerosol-induced atmospheric warming, which impacts regional climate, including the Indian monsoon.

We used high-altitude balloons to measure black carbon aerosols in the upper troposphere. These studies have shown how BC particles reach higher atmospheric levels via absorption-warming-convection cycles. This is important since the presence of BC particles can aggravate stratospheric ozone loss and delay the recovery of the stratospheric ozone hole by several decades.

Many industries and disciplines play a role in furthering our research. For instance, we use climate models that incorporate data on atmosphere, land surface, ocean and sea ice, aerosols, carbon cycle, dynamic vegetation, and atmospheric chemistry. These models require complex simulations with high spatial resolution (such as 3.5 km) and are computationally intensive.

This is a non-linear computational relationship, as an increase of two times in horizontal dimension will lead to an increase of 16 times in CPU time. Major challenges include the computing horsepower, computational science and mathematics, and software required to manage the model runs and programming models and parallelization. We require teraflop and petaflop computing as well as high grid resolution corresponding to 10 billion grid cells, which needs exascale computing.

In addition, there is a need for low-cost sensors to monitor air pollution. Air quality degradation is a major reason for the increased instances of pulmonary diseases including asthma. Particulate matter pollution can also be carcinogenic. To improve air quality, the first step is to monitor it at many locations in each city using low-cost sensors.

Another area that needs attention is the absence of a local climate model. The Indian climate science community relies on climate models developed abroad for climate predictions. Since these are based on measurements made elsewhere, they are not necessarily applicable to the Indian environment. To develop a climate model in India, we need a sustained effort over years, with many climate modelers and software specialists working together.

2. Your work requires you to measure, quantify and analyze a whole lot of data, in real time. Please comment.

Light-absorbing aerosols such as black carbon particles can impact climate, agriculture, satellite remote sensing and public health. They can alter cloud properties and precipitation patterns affecting the hydrological balance of the Earth-atmosphere system.

Therefore, accurate measurement of aerosols in the environment is important for answering crucial questions related to climate change. These measurements can be done from the ground, from space or from instrumented aircraft.

We established an aerosol-climate observatory at the Indian Institute of Science, Bengaluru, in 2001, with an aim to characterize aerosols and assess their radiative impacts. This lab has a number of sophisticated instruments to measure climate-sensitive parameters of aerosols along with surface radiation. The lab is now renowned for its aerosol research and is currently involved in conducting large-scale field campaigns over the Indian region as well as for designing and developing satellite sensors such as the multi-angle polarization imager.

Similar observatories are also maintained at Minicoy (Lakshadweep), Port Blair (Andaman and Nicobar), and Challakere, IISc’s second campus in northern Karnataka. The network now has about 40 to 45 observatories across India. In addition, field experiments are being conducted by our research group on board research ships and instrumented aircraft.

Since all this data is not available to us in real time, it can be quite challenging. We can only access the data when it is couriered or otherwise physically delivered to us. This is an area that we are looking to address.

3. How do you see the sophistication of technology with artificial intelligence, impacting not just your work but the greater call to environmental awareness and sustainability?

Artificial intelligence plays a very important role in disaster management involving weather and climate, irrigation, satellite remote sensing (including image processing), air quality prediction and so on. AI-based weather forecast models can be effectively utilized to alert and provide early warning about disasters and/or extreme weather conditions.

Soil moisture sensors, when used in conjunction with AI systems, can help optimize irrigation systems, especially in locations facing water shortages. Also, air quality model simulations and predictions, if linked with Google Maps, can provide location-based air quality alerts to citizens. Technology industries can play an important role here.

4. Given the potential impact of your studies on public health, it is clear that there needs to be close alignment among scientific, social and government communities. Do you see this happening efficiently and at larger scales? Can you use technology as an efficient conduit?

We have been making efforts toward this goal. We organize interactive sessions with members of parliament to create awareness on issues relevant to the society. The most recent one was on the impact of melting Himalayan glaciers on water security of the Indo-Gangetic basin. The next one being planned is on air quality and health, since the mitigation of air pollution requires involvement of policymakers.

We have established the South Asia regional office of the Future Earth, an international science-cum-policy initiative supported by United Nations agencies in Bengaluru. The aim is to (a) promote the implementation of specific activities over this region, (b) ensure that regional priorities are made part of the strategic development, (c) operate as the primary point of contact between researchers, research institutions, investors and other interested parties, and (d) provide up-to-date and timely information actively reaching out to researchers and stakeholders across this region.

Our research has helped drive a better understanding of the impact of aerosols on the Indian monsoon. A study published by the journal of the European Geophysical Union has demonstrated that aerosols actually increase the monsoon rains in contrast to the earlier belief that they decrease it. Such simulation was possible due to our description of light-absorbing aerosols in global climate models.

Using instrumented aircraft helps us provide observational evidence for the first time on the strong aerosol-induced warming close to the Himalayan region. We found that unless aerosol abundance over the Indo-Gangetic basin is urgently and substantially reduced, the result could affect water supply to the more than a billion people who live downstream.

5. And finally, what is next in line for your research? How will your findings map to the next set of studies?

One of our focus areas going forward will be to study the role of aerosols in free-space optical communication. FSO communication is a technology in which data is transmitted by propagation of light in free space allowing optical connectivity and is used in many areas, such as military applications, data services for mobile users, and for point-to-point or point-to-multipoint links from aircraft to ground or satellite to ground.¹ The presence of black carbon particles is generally seen as a hindrance for FSO communication systems. However, our investigations show that a strong, elevated BC layer at an altitude around 4.5 km enhances the atmospheric stability locally and leads to a large reduction in the atmospheric refractive index structure parameter (Cn2). Therefore, BC particles could actually be a boon in aerial FSO communication systems.

We also intend to further our research on the impact on the ozone layer of black carbon emissions from aircraft. Aircraft emissions during flights cause sharp and confined high-altitude layers of soot. Under certain conditions, this soot can be self-lofted and enter the lower stratosphere, where these particles can reside for a long duration in the absence of precipitation. One of the possible implications of the presence of BC in the stratosphere is a chemical reaction that results in the depletion of ozone. More observational studies using satellites, stratospheric balloons and modeling are required to address this important phenomenon, especially over regions with high aircraft traffic.

The most important question that we are trying to address in the near future is the role of aerosols in influencing cloud microphysical and radiative properties. We plan to establish a number of surface climate observatories and a series of field campaigns utilizing instrumented aircraft and ships. Monsoons are one of the largest organized atmospheric motions with well-defined periodicity and spatial characteristics, making them an ideal case study for evaluating models and testing their performance in simulating regional-scale phenomena. At present, there is significant uncertainty in modeling these systems and better data and improved parameterization are needed to close this gap. Our experiments will be useful both in understanding the processes at work and providing answers regarding the effects of aerosols on climate in a region where the perturbation is probably the highest.

¹https://www.hindawi.com/journals/ijo/2015/945483/