How much air pollution do rocket launches cause?

The billionaire space race has been a hot topic lately. Richard Branson of the Virgin Group went to space on July 11, 2021. Jeff Bezos of Amazon followed soon after on July 20, 2021. Elon Musk of Tesla and SpaceX plans on travelling sometime in the near future. The three are all seeking to commercialize the space industry, and they certainly have the financial means to do so. Unfortunately, space tourism will come at a significant environmental cost. Let’s take a closer look.

What kinds of pollutants are emitted by rocket launches?

Rockets require huge amounts of propellants to exit the atmosphere and into space. The composition of these propellants determines the kind of air pollutants that are emitted during the launch process. Below is a table showing the main four types that are used for rocket launches:

Propellant	Main Emissions	Launch System
Solid aluminum fuel, ammonium perchlorate (NH4ClO4) oxidizer, hydroxyl-terminated polybutadiene (HTPB)	Hydrochloric acid (HCl), water vapour (H2O), carbon dioxide (CO2), nitrogen oxides (NOx), alumina (Al2O3), black carbon (BC)	NASA’s Space Shuttle (0), ISRO’s GSLV (1)
Liquid oxygen, liquid hydrogen	Water vapour (H2O), hydrogen (H2), hydroxyl (OH), nitrogen oxides (NOx)	NASA’s Space Shuttle (1), ESA’s Ariadne 1/2/3/4 (3), ISRO’s GSLV (3)
Dinitrogen tetroxide (N2O4) fuel, unsymmetrical dimethylhydrazine (UDMH), hydrazine (N2H4)	Water vapour (H2O), nitrogen (N2), carbon dioxide (CO2), nitrogen oxides (NOx), black carbon (BC)	ESA’s Ariadne 1/2/3/4 (1, 2), Russia’s Proton (1, 2, 3), China’s Long March 1/2/3/4 (1, 2)
Liquid oxygen, kerosene	Carbon dioxide (CO2), water vapour (H2O), carbon monoxide (CO), hydroxyl (OH), nitrogen oxides (NOx), black carbon (BC)	Space X’s Falcon 9 (1, 2), Russia’s Soyuz (0, 1, 2)

What is the atmospheric impact of rocket launches?

Carbon dioxide (CO₂) emissions pose an issue when it comes to rocket launches. A typical long-haul plane flight creates between 1-3 tonnes of CO₂ per passenger. Rocket launches, on the other hand, generate between 50-75 tonnes of CO₂ per passenger. That being said, the number of rocket flights is currently very small: according to NASA, only 114 attempted orbital launches were made in 2020, compared to over 100,000 airplane flights per day. However, there is no telling how large the space tourism industry will become. Current estimates put the market at $2.58 billion in 2031, with a 17.15% growth each year of the next decade. 

Approximately two-thirds of propellant exhaust is released into the stratosphere (12 km-50 km) and mesosphere (50 km-85 km), where it can persist for at least 2-3 years. This is significant due to the climate impact of rocket emissions that are trapped in those layers.

The alumina (Al₂O₃), chlorine (converted from hydrochloric acid, HCl), nitrogen oxides (NO_x), hydroxyl (OH), and water vapour (H₂O) in rocket launch plumes all contribute to ozone depletion through chemical reactions in the Earth’s stratosphere. This naturally poses a risk to humanity, as ozone protects the Earth from harmful UV radiation.

Water vapour (H₂O) leads to increased cloud formation in the stratosphere and the mesosphere, and alumina (Al₂O₃) and black carbon (BC) can cause radiative forcing: Clouds and Al₂O₃ can reflect solar flux back into space, while Al₂O₃ and BC can absorb solar flux, which results in cooling. However, Al₂O₃ and BC can also absorb and trap the long-wave radiation from Earth, thus resulting in warming. A warmer stratosphere can result in faster ozone depletion by speeding up the chemical reactions that cause the loss. 

Unfortunately, the exact implications of propellant emissions on the climate remain unclear, as further study is needed in order to properly identify and quantify the potential impact of space launches. Nonetheless, it is evident that this is an issue that will continue to grow and affect Earth in the future.

What is the air quality impact of rocket launches?

The United State’s Federal Aviation Administration (FAA) conducted an environmental assessment on the potential impact of SpaceX Falcon launches from the Kennedy Space Center and the Cape Canaveral Air Force Station in Brevard County, Florida. To do this, they examined the air quality of the area under National Ambient Air Quality Standards (NAAQS) set by the Environmental Protection Agency (EPA). As most of the pollution from rocket launches is released higher up in the stratosphere and mesosphere, it is expected that the ground-level air quality impact would be lower. The NAAQS was compared to the historical ambient air concentrations of criteria pollutants in the region:

Pollutant	Averaging Time	Nearest Monitoring Station	Maximum Measured Concentration (ppm, except PM in µg/m3)
			2013	2014	2015	2016	2017
O3	8 Hours	Palm Bay-Melbourne-Titusville	0.063 (4th max)	0.063 (4th max)	0.059 (4th max)	0.061 (4th max)	0.061 (4th max)
CO	1 Hour	Orlando-Kissimmmee-Sanford	1.1	1.8	1.5	1.9	2.8
	8 Hour		1.0	1.5	1.2	1.2	1.4
NO2	1 Hour	Orlando-Kissimmee-Sanford	0.034	0.036	0.025	0.029	0.030
	Annual (mean)		0.005	0.005	0.004	0.004	0.004
SO2	1 Hour	Orlando-Kissimmee-Sanford	0.003	0.007	0.003	0.002	0.005
	24 Hour		0.0004	0.0023	0.0005	0.0013	0.008
PM10	24 Hour	Palm Bay-Melbourne-Titusville	54 (2nd max)	44 (2nd max)	47 (2nd max)	38 (2nd max	49 (2nd max)
PM2.5	24 Hour	Palm Bay-Melbourne-Titusville	21	14	12	10	20
	Annual		5.7	5.8	5.2	5.2	6.6

As can be seen in the figure above, there were no exceedances of the NAAQS throughout the years at a primary NASA launch centre. It would be easy to say that rocket launches in fact do not have a significant impact on ground-level air quality; however, this data is for ambient air pollution. This means that we do not know what the exact air quality impact of individual launches are.  

Once again, there remains a lack of data surrounding propellant emissions. It would be great if space companies and government agencies could see space exploration as the environmental risk it is and devote time and resources into collecting air quality data around launch sites. Preventive measures and interventions are key. Once the space tourism industry grows into the billions, it may be too late.