Sources and References

Primary texts — Seinfeld and Pandis, Atmospheric Chemistry and Physics: From Air Pollution to Climate Change, 3rd ed. (Wiley). Cooper and Alley, Air Pollution Control: A Design Approach, 4th ed. (Waveland).

Supplementary texts — Hinds, Aerosol Technology: Properties, Behavior, and Measurement of Airborne Particles, 2nd ed. (Wiley). Jacob, Introduction to Atmospheric Chemistry (Princeton). Godish, Davis, and Fu, Air Quality, 5th ed. (CRC Press).

Online resources — U.S. EPA AirNow and AP-42 emission factor compendium. WHO Global Air Quality Guidelines (2021). ISO 16000 series on indoor air. European Environment Agency EMEP/EEA emission inventory guidebook. MIT OCW 1.84J Atmospheric Chemistry. Harvard Jacob lecture notes on atmospheric chemistry (open).

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Chapter 1: Air Pollution Fundamentals

1.1 Pollutants and Scales

Criteria pollutants — particulate matter (PM₁₀, PM₂.₅), ozone, nitrogen oxides, sulfur dioxide, carbon monoxide, and lead — are regulated under the U.S. Clean Air Act and analogues. Hazardous air pollutants include heavy metals and many volatile organic compounds. Indoor air adds formaldehyde, radon, and bioaerosols. Pollution problems span scales: microenvironmental (indoor), urban (smog), regional (acid deposition), hemispheric (O₃, PM transport), and global (stratospheric ozone, climate forcing).

1.2 Concentration Units and Conversions

Gaseous concentrations are given in parts-per units or mass per volume. At \( T, p \),

\[ C \,[\mu\mathrm{g/m^3}] = \frac{C\,[\mathrm{ppb}] \cdot M}{22.414} \cdot \frac{273.15}{T}\cdot\frac{p}{101.325} . \]

Particulate concentrations are given in µg/m³ of ambient air; size distributions are more informative than mass alone.

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Chapter 2: Emission Sources and Inventories

2.1 Source Classification

Point sources (stacks, vents), area sources (residential heating, dry cleaners), mobile sources (on-road, non-road), and biogenic sources (vegetation VOC, soil NO). Emission rates \( E \) are estimated from

\[ E = A \cdot EF \cdot (1 - \eta/100) , \]

where \( A \) is activity, \( EF \) an EPA AP-42 or EMEP emission factor, and \( \eta \) a control efficiency. Uncertainty grows downward from fuel-based combustion (well-characterized) to fugitive and biogenic sources.

2.2 Combustion Chemistry

Thermal NO forms through the Zeldovich mechanism at flame temperatures:

\[ \mathrm{O} + \mathrm{N_2} \rightarrow \mathrm{NO} + \mathrm{N}, \qquad \mathrm{N} + \mathrm{O_2} \rightarrow \mathrm{NO} + \mathrm{O} . \]

The steady-state NO production is strongly superlinear in flame temperature, motivating flue-gas recirculation, staged combustion, and premixing strategies. Fuel NO arises from nitrogen bound in coal and biomass; prompt NO matters in fuel-rich flames.

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Chapter 3: Atmospheric Transport and Chemistry

3.1 The Gaussian Plume

For a continuous point source, the steady-state concentration downwind is

\[ C(x,y,z) = \frac{Q}{2\pi u \sigma_y \sigma_z} \exp\!\left(-\frac{y^2}{2\sigma_y^2}\right)\left[\exp\!\left(-\frac{(z-H)^2}{2\sigma_z^2}\right)+\exp\!\left(-\frac{(z+H)^2}{2\sigma_z^2}\right)\right] , \]

with \( H \) the effective stack height and dispersion parameters \( \sigma_y, \sigma_z \) from Pasquill–Gifford stability classes. The model is exact for homogeneous turbulence and a perfectly reflecting ground, and it remains the workhorse of regulatory screening (AERMOD adds similarity scaling and terrain).

3.2 Tropospheric Photochemistry

Ozone is produced in VOC/NOₓ systems through the cycle

\[ \mathrm{NO_2} + h\nu \rightarrow \mathrm{NO} + \mathrm{O}, \qquad \mathrm{O} + \mathrm{O_2} + M \rightarrow \mathrm{O_3} + M , \]

with ozone destroyed by \( \mathrm{NO} + \mathrm{O_3} \rightarrow \mathrm{NO_2} + \mathrm{O_2} \). In the absence of peroxy radicals this cycle produces no net O₃. VOC oxidation introduces RO₂ and HO₂ that convert NO to NO₂ without consuming O₃, shifting the null-cycle equilibrium upward. The nonlinear response — VOC- vs NOₓ-limited regimes — dictates control strategy.

3.3 Aerosol Processes

Aerosol number distributions span nucleation, Aitken, accumulation, and coarse modes. Coagulation, condensation, and dry deposition follow:

\[ \frac{dN}{dt} = -\tfrac{1}{2}\int\!\int K(v,v') n(v) n(v')\,dv\,dv' + \cdots \]

Hygroscopic growth under relative humidity modifies optical and respiratory properties. Secondary organic aerosol from VOC oxidation contributes a large, uncertain fraction of urban PM₂.₅.

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Chapter 4: Control Technologies

4.1 Particulate Control

Cyclones rely on centrifugal separation; cut diameter \( d_{pc} \) scales as

\[ d_{pc} = \sqrt{\frac{9 \mu W}{2\pi N_e V_i (\rho_p - \rho)}} , \]

where \( N_e \) is the number of effective turns. Electrostatic precipitators obey the Deutsch–Anderson equation \( \eta = 1 - \exp(-w A/Q) \) with migration velocity \( w \). Fabric filters combine inertial impaction, interception, and diffusion; pressure drop and cleaning cycles set operating cost.

4.2 Gaseous Control

Wet scrubbing, absorption towers (with height of transfer unit HTU and number of transfer units NTU), selective catalytic reduction of NOₓ with ammonia, selective non-catalytic reduction, flue-gas desulfurization by limestone slurry, and thermal/catalytic VOC oxidation constitute the main toolkit. Choice among them depends on mass-transfer requirements, catalyst sensitivity, and disposal of secondary wastes.

4.3 Indoor Air

Source control, ventilation, and filtration form the classical triad. Filter performance is rated by MERV (ASHRAE 52.2) or ISO 16890 (ePM₁, ePM₂.₅, ePM₁₀). HEPA filters remove ≥99.97% of 0.3 µm particles. Activated-carbon sorbents and photocatalytic oxidation address gaseous pollutants, though byproducts (e.g., formaldehyde from incomplete oxidation) must be managed.

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Chapter 5: Measurement, Modelling, and Monitoring

5.1 Reference and Sensor Methods

Federal reference methods use gravimetric filters and chemiluminescence (NOₓ), UV absorption (O₃), pulsed fluorescence (SO₂), and β-attenuation or TEOM for PM. Low-cost optical sensors (e.g., Plantower, Alphasense) provide dense spatial coverage but require co-location calibration against FRM for trend reliability.

5.2 Models Across Scales

Eulerian grid models (CMAQ, WRF-Chem, GEOS-Chem) solve the advection–diffusion–reaction equation

\[ \frac{\partial C_i}{\partial t} + \nabla\cdot(\mathbf{u}C_i) = \nabla\cdot(\mathbf{K}\nabla C_i) + R_i + E_i - L_i \]

on nested grids. Lagrangian particle models (HYSPLIT) trace back-trajectories for source attribution. Receptor models (CMB, PMF) apportion measured PM to source fingerprints without emission inventories.

5.3 Air-Quality Index and Communication

The AQI is a piecewise-linear map from concentration to a 0–500 scale, with health categories. Risk communication is engineering: thresholds must be understandable, action-guiding, and aligned with scientific evidence.

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Chapter 6: Health, Economics, and Policy

6.1 Exposure–Response

Epidemiological studies link ambient PM₂.₅ to all-cause, cardiovascular, and respiratory mortality through relative risks of the form \( \mathrm{RR} = \exp(\beta \Delta C) \). The Global Burden of Disease integrates these with baseline rates to estimate attributable deaths. Integrated exposure–response functions fit nonlinearities over wide concentration ranges.

6.2 Cost–Benefit Analysis

Regulatory impact analysis under Executive Order 12866 (and similar regimes elsewhere) monetizes avoided mortality and morbidity using the value of a statistical life and willingness-to-pay studies, discounts future benefits, and compares to compliance costs. Uncertainty bounds, distributional impacts, and environmental justice are increasingly explicit.

6.3 Climate Co-Benefits

Short-lived climate forcers — methane, black carbon, tropospheric ozone — couple air quality and climate. Reducing methane leakage and diesel black carbon lowers warming within decades and improves air quality simultaneously. Integrated assessment frameworks quantify co-benefits and co-harms, allowing climate and air policy to be designed as a single engineering system rather than two disjoint regulatory silos.