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Discerning Local versus Non-local Influences of PM2.5

Discerning Local versus Non-local Influences of PM2.5. Background and Rationale Influence of wind speed on local concentrations Mid-Atlantic Rural Sites PM2.5 Vs Surface Wind Speed Mid-Atlantic Urban Sites PM2.5 Vs Surface Wind Speed Seasonal Urban-Rural Difference Conclusions

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Discerning Local versus Non-local Influences of PM2.5

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  1. Discerning Local versus Non-local Influences of PM2.5 • Background and Rationale • Influence of wind speed on local concentrations • Mid-Atlantic Rural Sites PM2.5 Vs Surface Wind Speed • Mid-Atlantic Urban Sites PM2.5 Vs Surface Wind Speed • Seasonal Urban-Rural Difference • Conclusions • Resource Links Contact: Bret Schichtel, Bret@mecf.wuslt.edu

  2. Background and Rationale • At any given location the PM concentration is the result of the PM mass originating from non-local sources transported in and PM mass originating from local sources. [What is ‘local’??] • The local/non-local contributions depend on emissions, transport and aerosol formation and removal processes, so there is no “typical” non-local concentration. • Quantifying the local contributions identifies the part of the PM problem that can be controlled locally.

  3. Influence of wind speed on local concentrations • The concentration C is equal to the sum of the background (Co) and local contribution (QL/UH) • Assuming a fixed source region length (L), emission rate (Q) and mixing height (H) as the wind speed (U) increases the concentration from the local sources decreases asymptotically approaching the background concentration.

  4. PM2.5 Vs Surface Wind Speed at Urban and Rural Sites The PM2.5 at the urban sites during the cold season (Nov - March) decline sharply (60%) with increasing wind speeds compared to the rural sites (30%). This implies the urban PM2.5 is dominated by local sources.

  5. Seasonal Urban-Rural Difference • The excess PM2.5 at Washington DC ranges from >10 mg/m3 in the winter to 1-2 mg/m3 in the summer. • The Phoenix excess PM2.5 ranges from 11 - 16 mg/m3 in the winter to 3 mg/m3 in the summer.

  6. Conclusions • Mid-Atlantic and Southwest urban centers are dominated by local sources during the winter. • At the Mid-Atlantic urban sites, the summer local sources contribute about 10% of the PM mass compared to up to 70% in the winter. • At the urban Southwest, the local sources contribute about 30% of the summertime PM mass compared to about 80% in the winter.

  7. Resource Links • Workbook Table of Contents • Comment and Feedback Page • Applications / Reports • Data sets used in the Applications • Methods and tools used in the Applications

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