hazeforming

Hazeforming refers to the processes and conditions that produce atmospheric haze, a visible reduction in air clarity caused by fine particles and droplets suspended in the air. Haze can arise from direct emissions of aerosol particles (primary aerosols) or from chemical reactions in the atmosphere that create new particles (secondary aerosols). It is a common feature of urban, industrial, and wildfire-affected regions and can be natural or anthropogenic in origin.

Primary aerosols include dust, soot, sea salt, and bioaerosols released directly from sources such as road traffic, biomass burning, construction, and windblown dust. Secondary aerosols form when gases such as sulfur dioxide, nitrogen oxides, and volatile organic compounds oxidize and condense into sulfate, nitrate, and organic aerosol particles. Water uptake by hygroscopic particles then increases particle size and humidity, enhancing haze under humid conditions.

Meteorological conditions influence haze formation and persistence. Inversions, low wind, high humidity, and stagnant air trap pollutants near the surface, while atmospheric chemistry driven by sunlight can accelerate secondary aerosol formation in daytime.

Sources of haze vary by region. Urban and industrial areas commonly exhibit traffic emissions, coal or oil combustion, and industrial processes. Wildfires and agricultural burning are major natural or semi-natural contributors. Natural dust from deserts and biogenic particles can also contribute.

Impacts include reduced visibility, impaired outdoor activities, health effects such as respiratory and cardiovascular issues, and climate effects through scattering and absorption of sunlight. Measurements rely on ground-based sensors of PM2.5/PM10, aerosol optical depth, and visibility, complemented by satellite data.

Mitigation focuses on emission reductions, clean energy transitions, emission controls, and rapid response to wildfires. Public health advisories during haze events help reduce exposure. Research continues to improve understanding of aerosol sources, chemistry, and climate interactions.