(HW 10)Anthropogenic NOₓ Emissions and Urban Ozone Formation

Primary anthropogenic source of NOₓ emissions globally

Fossil fuel combustion

Short residence time of NOₓ in the troposphere

It is rapidly removed through chemical reactions and deposition

Condition favoring N₂O₅ formation and accumulation

Cold nighttime conditions

Long-range NOₓ reservoir due to thermal stability

PAN

Reason NO₃ doesn't accumulate during the day

It is photolyzed by sunlight

TRUE about biogenic VOC emissions in summer

They dominate VOC emissions and contribute significantly to ozone formation

Main fate of isoprene under low-NOₓ conditions

Formation of ISOPOOH and IEPOX

Key termination product of isoprene oxidation in high-NOₓ

Organic nitrates (RONO₂)

Compounds most reactive with OH, NO₃, and O₃ due to double bonds

Alkenes

Reason trees like oaks emit isoprene

To protect leaves from heat stress and temperature fluctuations

Structural distinction between α-pinene and β-pinene

α-pinene has an endocyclic double bond, β-pinene has an exocyclic double bond

Major product of α-pinene oxidation under low-NOₓ

Hydroxyl hydroperoxides

Dominant atmospheric fate of SO₂

Oxidation in clouds (aqueous-phase chemistry)

VCPs and their difference from traditional VOC sources

VCPs are consumer/industrial products (e.g., paints, cleaners) that emit VOCs not related to combustion; they now account for ~50% of urban VOCs.

Importance of VCPs for urban ozone formation

VCPs emit reactive VOCs that significantly contribute to ozone formation, especially in VOC-limited cities like NYC.

Comparison of monoterpene emissions from VCPs to forests

Urban VCP monoterpene emissions can rival or exceed biogenic emissions from forests.

Conclusion about NOₓ vs. VOC reductions for ozone control

VOC reductions (esp. VCPs) are more effective in urban near-field; NOₓ reductions help more downwind.

Role of WRF-Chem and box models in the study

WRF-Chem modeled 3D regional ozone; box model evaluated NYC plume and VOC sensitivity.

Effect of including oxygenated VCP chemistry on pollutant predictions

It slightly increases ozone but significantly boosts PAN and alters NOₓ cycling.

Reason to regulate VCPs along with vehicle emissions

VCPs are major urban VOC sources not well-regulated; controlling them could reduce ozone, especially during heatwaves.