Chapter 4 How Satellite Data Complement GroundBased Monitor

Chapter 4: How Satellite Data Complement Ground-Based Monitor Data 3: 15 – 3: 45

Sources of Data for Air Quality Analysis • There are three major sources of data for air quality analysis: – Ground-based monitor data – Satellite data – Model forecast data • For a complete picture of air quality, need to use all three sources, when possible!

Ground-Based Monitor Data • Strengths: – Accurate, precise measurements of specific pollutants (PM 2. 5, PM 10, O 3, etc. ). – Measurements at surface, where people live and breathe air. • Limitations: – Measurements only in areas where monitors are located; typically, there are large gaps in any country’s monitor network. – Monitors are expensive to purchase and operate.

Satellite Data • Strengths: – Global, regional, and local coverage – satellites provide information for areas where no ground-based monitors exist. – Routine measurements are made daily. – Data are “free” – no cost to users with access to the internet. • Limitations: – Measurements are for entire vertical column of atmosphere, not specific to surface. – Clouds block measurement of many air quality satellite parameters. – Temporal and spatial resolution of satellites can limit data availability.

Example: Satellite Data

Model Forecast Data • Strengths: – Forecasts provide information on future air quality conditions; advanced notice allows governments to take action to protect public health. • Limitations: – Model forecasts are NOT measurements! They are predictions of future air quality conditions. – Air quality models are complex combinations of numerical weather models and atmospheric chemistry, physics, and emissions models – the sum is only as good as the individual parts. – Model output can be difficult to interpret for novices or non -experts.

Example: Model Forecast Data

How Can Satellite Data Complement Ground. Based Monitor Data? • Satellites make global measurements, so we can use them to supplement ground-based measurements from a monitor network. • Since satellites measure the total pollutant concentration in a vertical column of atmosphere, it is necessary to correlate satellite data with ground-based monitor data. • Once we know the relationship between satellite and ground-based data, we can apply satellite data to areas where there are no ground-based monitors and obtain and estimate of surface pollutant concentrations.

Example: Correlation between MODIS AOD and PM 2. 5 for One Location in U. S. Baltimore, Maryland 2005 Terra

Example: Correlation between MODIS AOD and PM 2. 5 for May 2007 in U. S. • Correlation varies by: § Region and season § Vertical aerosol distribution and properties § Meteorological conditions such as relative humidity and boundary layer height • AOD retrievals are also less accurate over bright surfaces such as desert or snow. Image generated by Giovanni , NASA GES DISC

Visualization of Satellite and Monitor Data • Satellite imagery and ground-based monitor data can also be visualized together to provide a more complete picture of air quality conditions. • Try using Google Earth or the mapping products on SERVIR. net to visualize air quality data! Haze Smoke Eastern United States June 13, 2008

Interpretation of Satellite Images • Quantitative for PM 2. 5 and NO 2 • Qualitative for SO 2 • Bottom line: use satellite images for information about the distribution and transport of pollutants, but not about the exact concentrations of pollutants. • Don’t forget: if satellites indicate the presence of pollutants, it doesn’t mean concentrations are high at the surface. The pollution could be aloft in the atmosphere, above the surface.

Air Quality Analysis: Final Thoughts • For best results, look at all three types of data when you are conducting an air quality analysis: – Ground-based monitor data – Satellite data – Model forecast data • The three data sources each convey different information! • Don’t forget the strengths and weaknesses of each type of data.