Objectives and Questions

Emissions, air quality, and climate in urban areas

AEROMMA will determine organic emissions and chemistry, including of understudied VCPs, in the most populated urban areas in the United States, to better understand the impact on ozone and aerosol formation, and to study their relative importance on urban air quality.

  1. How well do current emission inventories quantify the flux of anthropogenic VOC emissions over North American cities, including VCPs, mobile sources, cooking, and industrial facilities?
  2. How does the relative distribution of VOC emissions vary by city and population density, influencing the ratio of VCP to mobile source emissions?
  3. What chemical tracers can be used to source apportion VOCs amongst VCPs, energy-related, cooking, and biogenic sources?
  4. How have VOC emissions changed between AEROMMA and previous urban measurements (e.g., NEAQS 2002, ICARTT 2004, TEXAQS 2006, CalNex 2010, SENEX 2013, WINTER 2015, NYICE/LISTOS 2018, FIREX-AQ 2019, etc.)?
  5. What is the composition of gas- and aerosol phase organics in the urban atmosphere, including aromatics, alkanes, terpenes, cycloalkanes, oxygenated VOCs (including water-soluble organics such as alcohols, esters, glycols, and glycol ethers), and organic aerosol?
  6. How do understudied oxygenated VOCs from VCPs and their oxidation products affect atmospheric oxidant budgets, and how well do models represent oxygenated VOC chemistry, including heterogeneous reactions?
  7. What is the relative role of anthropogenic versus biogenic VOCs on ozone and organic matter formation, and how does this vary between vegetated and non-vegetated regions?
  8. What is the formation rate of ozone and particulate matter in urban outflow, and to what extent do non-traditional sources (e.g., VCPs and cooking) affect the amount of ozone and aerosols formed?
  9. How do organics affect the evolution of particle size, number distribution, and aerosol optical properties (e.g., brown carbon) in urban outflow, and to what extent does urban outflow contribute to cloud condensation nuclei (CCN) formation?

Determine reactive nitrogen emissions and chemistry in major urban corridors (i.e., urban core to suburban and outlying rural areas) to understand the current importance of combustion and non-combustion sources, continue the trend analysis and determine changes in the reactive nitrogen cycle chemistry and its influence on ozone and aerosol formation.

  1. How well do current emission inventories quantify the flux of anthropogenic nitrogen oxides (NOx = NO + NO2) over North American cities, including from mobile sources, buildings, industrial facilities, and outlying agricultural regions and power generation?
  2. How have NOx emissions changed between AEROMMA and previous urban measurements (e.g., NEAQS 2002, ICARTT 2004, TEXAQS 2006, CalNex 2010, SENEX 2013, WINTER 2015, NYICE/LISTOS 2018, FIREX-AQ 2019, etc.)?
  3. How does the NOx lifetime affect the interpretation of satellite retrievals of nitrogen dioxide (NO2) as a constraint on urban to rural NOx emission inventories?
  4. What is the relative role of combustion (e.g., mobile sources) versus non-combustion sources (e.g., agricultural soils and VCPs) of NOx, nitrous acid (HONO), ammonia (NH3), and VOCs on ozone and ammonium nitrate formation?
  5. How do the formation rates of ozone and particulate matter in urban outflow evolve from high to low NOx regions?
  6. What is the speciation of oxidized reactive nitrogen in urban outflow in 2021, and does it differ substantially from previous campaigns due to evolving NOx-VOC chemistry due to changes in dominant emission sources?

Determine the fraction of urban VOC and NOx emissions associated with emissions of CO2 and methane (CH4) from transportation, buildings, industry, and landfills to quantify co-benefits between managing air quality and the carbon cycle.

  1. How well do current emission inventories quantify the flux of anthropogenic CO2 and CH4 emissions over North American cities, including from mobile sources, buildings, industrial facilities, natural gas infrastructure, and landfills?
  2. How does the flux of CO2 and CH4 emissions vary between North American cities, including as a function of population density and age of energy infrastructure?

Investigate urban and coastal meteorology, to better understand extreme heat on urban air quality, urban heat islands, and the role of long-range transport versus local sources of air pollution.

  1. How does extreme heat affect urban and coastal meteorology, photochemistry, and ozone and aerosol formation?
  2. How does the urban canopy affect urban heat islands, land-sea breezes, and planetary boundary layer (PBL) dynamics?
  3. What is the local versus regionally- and continentally-transported contributions to ozone, and how is the relative contribution affected by heatwaves?

Investigating the interface of urban and marine atmosphere

AEROMMA will provide observations at the interface of the marine atmosphere and the urban airshed to quantify what impact marine emissions have on urban air quality and composition and the impact of urban outflow on marine chemistry. Observations will resolve the relative contributions to SO2, sulfate aerosols, and CCN from biogenic and anthropogenic sulfur sources

  1. What are the relative contributions of urban, ship emissions, secondary marine production to the SO2 budget?
  2. How does anthropogenic NOx impact oxidation of sulfur and the distribution of secondary species in the marine atmosphere?
  3. What impacts do marine halogens have on the atmospheric oxidant budget through the photolysis of key marine species, e.g. ClNO2, Cl2, and BrO?
  4. Are marine gases important factors for ozone formation in coastal urban regions?
  5. Where is the transition from isomerization chemistry forming HPMTF to bimolecular NO chemistry forming SO2?

Utilize observations of aerosol abundance and composition to understand the impact of the various sources of biogenic and anthropogenic emissions on aerosol and CCN formation.

  1. What fractions of CCN producing aerosol is natural versus controlled by anthropogenic emissions?
  2. How well do regional and global models predict the influence of urban and marine secondary aerosols on climate?
  3. How will the distribution of aerosols and CCN sources change in the future as a result of Earth's warming and changes in anthropogenic emissions?
  4. Does the mixing of urban and marine aerosols impact SOA formation and the atmospheric fate of aerosols?

Investigation of the remote marine atmosphere

AEROMMA will exploit the range and capabilities of the NASA DC-8 to sample the remote marine atmosphere in regions with (1) limited impacts from anthropogenic sources, (2) high atmospheric burden from biogenic emission, (3) stable meteorology, and (4) a well-defined marine boundary layer.

Investigation of the emissions and chemistry in the remote marine atmosphere that drive the formation of secondary products and marine aerosols. Flux observations will be used to better quantify the air-sea exchange of VOCs to better understand the atmospheric budget of gas-phase precursor species in the remote atmosphere.

  1. What are the sources of VOCs and volatile sulfur in the remote marine atmosphere?
  2. How well do we understand the net oceanic flux of biogenic sulfur?
  3. How do primary oceanic emissions of sea spray impact the marine aerosol burden, spatial distribution and properties?
  4. At what rates are atmospheric gases and aerosol deposited to the ocean's surface?

Observations to better characterize the marine sulfur oxidation cycle and secondary aerosol formation and dependencies on key parameters such as temperature, NOx, and background aerosol.

  1. How well do we understand oxidation of biogenic sulfur and VOCs in the remote marine atmosphere?
  2. How does the oxidation of biogenic marine emissions couple to aerosol production and growth?
  3. What are the processes that drive the removal of secondary gases and aerosols throughout marine boundary layer?
  4. How will the products from the oxidation of DMS be impacted by changes in temperature as a result of changes in Earth's climate?

Utilize measurements throughout the marine boundary layer in both clouded and cloud-free conditions to quantify air-sea exchange of trace gases and production of primary aerosol, and aqueous aerosol and cloud scavenging. We aim to better identify the linkages between marine emissions and aerosol abundance to improve predictions of marine aerosol-cloud-climate interactions in a changing climate. This data set will be valuable for evaluating models identifying the impact of a changing climate on CCN sources, cloud albedo and Earth's radiative budget

  1. What fraction of the organic aerosol is primary versus secondary at various time scales?
  2. How well do current models represent primary and secondary marine aerosols and their radiative properties, and what are the largest associated uncertainties?
  3. How important is the formation of secondary aerosol from aqueous-phase processes?
  4. How do aerosol optical properties evolve due to secondary production and particle phase transitions?
  5. What are the sources of new particles in the remote troposphere, how rapidly do they grow to CCN-active sizes, and how well are these processes represented in CCMs?