Climate change and urban air pollution are two of society’s great challenges. Our research investigates how climate, air quality, and land cover interact from urban to global scales. We also investigate practical solutions for mitigating climate change and air pollution in urban areas.
- Solutions for Countering Urban Warming and Air Pollution
- Climate-Aerosol Interactions
- Characterizing Aerosol Emissions from Combustion Sources
- Land-Atmosphere Interactions
Solutions for Countering Urban Warming and Air Pollution
Over 50% of the world’s population lives in cities and this fraction is projected to increase throughout the century. Many urban areas are hotter than surrounding rural areas due to the urban heat island effect. The urban heat island effect occurs from a combination of factors including a city’s abundance of low albedo / thermally massive materials (e.g., asphalt concrete) and lack of vegetation. Climate model projections indicate that global climate change will further warm cities over the next decades. The urban heat island effect and climate change also have the potential to exacerbate air pollution.
The two methods that we investigate for reducing urban warming include 1) using “cool” urban land cover and 2) reducing black carbon aerosol emissions. “Cool” land cover can include either reflective surfaces (e.g. reflective cool roofs or pavements) or urban vegetation that evaporatively cools surroundings. Black carbon aerosols absorb sunlight and warm its surroundings, so reducing concentrations can cool the atmosphere. Specific projects include:
- Using a regional climate model to determine the potential for cool roofs, walls, or pavements to reduce urban temperatures
- Using a regional climate model to determine the impacts of cool roof, wall, or pavement adoption on ozone and particulate matter concentration.
- Developing a new method using remote sensing (i.e. high resolution aerial imagery) to determine the albedo of roofs for entire cities. Research showed that small residential homes (as opposed to large commercial buildings) make up most of a city’s roof area; the majority of these residential roofs have low albedo. Results contributed to a policy adopted in 2013 in Los Angeles requiring the use of “cool roofs” on homes.
- Observations of black carbon emissions from various sources including diesel trucks. Past work showed the importance of “high emitter” diesel trucks, which resulted in policies to retrofit or retire older “dirty” trucks rather than regulate only new trucks.
- Determining the energy use implications of retrofitting an office building with a building integrated photovoltaic roof (observations and building energy modeling)
Atmospheric aerosols (i.e. particles) markedly affect global and regional climate. They interact directly with solar radiation, modify the thermal structure of the atmosphere, and affect clouds. On the whole, aerosols cool the climate and thus mask warming caused by greenhouse gases. However, one type of aerosol called black carbon absorbs solar radiation and warms the atmosphere. Black carbon is widely thought to be the second most important agent of global warming after CO2.
Our primary research tools are climate models (both global and regional) and observations (both ground and satellite based). Black carbon has been one of our main focus areas though other aerosols have also been studied. Studies focus on:
- Importance of the altitude of black carbon on climate forcing and response (using climate models)
- Evaluating aerosol-cloud interactions in global climate models using satellite observations
- Using observations to characterize climate-relevant properties of emissions sources. This includes determination of the mixing state of black carbon particles using our single particle soot photometer (SP2).
- Using climate models to assess the potential benefits and unintended consequences of using geoengineering to counter global climate change. Approaches include mimicking volcanoes by increasing sulfate loadings in the stratosphere and increasing the reflectivity of stratocumulus clouds.
Characterizing Aerosol Emissions from Combustion Sources
Combustion processes constitute one of the largest sources of aerosols. Aerosols affect both regional and global climate and have deleterious health consequences. Estimates of speciated global aerosol emissions are very uncertain. Improved characterization of aerosol emissions from various sources allows for better understanding of climate/health consequences and more effective policies for reducing emissions.
We focus on characterizing aerosols emissions using targeted observations. Our current focus is diesel combustion. We are especially interested in black carbon emission factors and mixing state using our single particle soot photometer (SP2).
The land surface and atmosphere exchange energy, water, and carbon, and represent a tightly coupled system.
We use climate models to increase fundamental understanding of this complex coupled system. Land-atmosphere interactions include those described above in “Solutions for Countering Urban Warming and Air Pollution”. Study of natural environments is also important. Past research has investigated the impact of aforrestation on climate, the impact of CO2 physiological forcing on global climate, and surface latent and sensible heating as a zero-order climate forcing agent.
Impacts of renewable energy adoption on air pollution
Solving the global climate problem is one of our society’s greatest environmental challenges. Mitigating climate change requires wide-scale adoption of carbon-free energy systems. Adopting such energy systems can have co-benefits on air pollution.
We are exploring the air pollution co-benefits of various scenarios of renewable energy adoption in the greater Los Angeles area using a state-of-the-science climate-chemistry model.