Dissertations and Theses

Date of Degree


Document Type


Degree Name

Doctor of Public Health (DPH)


Environmental, Occupational, and Geospatial Health Sciences


Ilias G. Kavouras

Committee Members

Glen Johnson

David W. Dubois

Subject Categories

Public Health


Air Pollution


Background. Exposures to fine particulate matter (PM2.5; particles with diameter less than 2.5 μm) and ozone (O3) affect premature respiratory and cardiovascular mortality, morbidity and contribute to the development and progression of sub-clinical and clinical disease. Climate change affects air quality directly by modifying the thermodynamic properties of formation mechanisms and transport patterns, and indirectly, through increased emissions of PM2.5 and O3 precursors. The resultant changes in air quality influence human health outcomes through mechanisms of varying scale, timing, and complexity. PM2.5 and O3 levels have been declining due to the implementation of fuel consumption standards and emission controls in transportation and industrial sectors leading to significant reductions of emissions of gaseous precursors of particulate sulfate and nitrate aerosol and, ozone. Today, the declining trends of emissions and resultant ambient levels are not converging; ambient PM2.5 levels are stabilizing and O3 levels are increasing above the national ambient air quality standards for the protection of human health (NAAQS). Local, regional and global changes in meteorology, climatology, chemistry and emissions have been implicated. This study aims to understand the trends and drivers of PM2.5 and O3 in the New York City metropolitan area, the largest megacity in North America, over the 2007-2017 period.

Methods. Daily 8-hr and 1-hr O3 and nitric oxide (NO) concentrations at 16 sites, 24-hr and 1-hr PM2.5 mass concentrations at 14 sites and PM2.5 chemical speciation concentration at 4 sites located in the New York/New Jersey metropolitan statistical area (MSA) were retrieved from the US Environmental Protection Agency (EPA) Air Data for the 2007-2017 period. Annual emission inventories for 2007 and 2017 were acquired from EPA National Emissions Inventory (NEI). The number and area burnt by natural and human-ignited wildfires were acquired from the National Interagency Fire Center (NIFC). Meteorological and climatological data were obtained from the National Oceanic and Atmospheric Administration (NOAA) National Climate Data Center (NCDC). Ambient daily O3 and PM2.5 concentrations were tested for normality using the Shapiro-Wilk test. The significance of difference among sites was assessed with the non-parametric Kruskal-Wallis at α=0.05. The monthly mean concentration was computed for months with more than 75% of measurements. The annual trend was computed by applying the non-parametric sequential Mann-Kendall test at a confidence level of 95%. The spatial variability of measurements was assessed using the paired absolute (ΔC) and the percent relative (%ΔC/Ref) concentration difference, the coefficient of divergence (COD) and the local Moran’s I and its significance. The Interagency Monitoring of Protected Visual Environments (IMPROVE) PM2.5 mass reconstruction scheme was used to identify the major aerosol types. The USEPA Positive Matrix Factorization (PMF) model (Version 5.0) was applied to apportion PM2.5 sources. The optimized solution was selected using previously reconciled source profiles and applicable statistical tools using a sequence of rotational and bootstrap runs.

Results. The highest daily 8-hr max O3 concentrations varied from 90 to 111 parts per billion volume (ppbv) with the highest concentrations measured perimetrically to NYC urban agglomeration. The monthly 8-hr max O3 levels have been declining for most of the peri-urban sites but increasing (from +0.18 to +1.39 ppbv/year) for sites within the urban agglomeration. Slightly higher O3 concentrations were measured during weekend than those measured during the weekdays in urban sites probably due to reduced O3 titration by NO. Significant reductions of locally emitted anthropogenic nitrogen oxides (NOx) and volatile organic compounds (VOCs) may have triggered the transition from VOC-limited to NOX-limited conditions, with downwind VOCs sources being critically important. Strong correlations between the monthly 8-hr max O3 concentrations and wildfires in Eastern US were computed. Larger number and more destructive wildfires in the region were ignited by lightning for years with moderate and strong La Niña conditions. Ambient PM2.5 mass levels declined on average by 47%, at a rate of -0.61 ± 0.01 μg/m3/y in urban locations and -0.25 ± 0.01 μg/m3/y in upwind and peri-urban locations over the 2007-2017 period. The strong spatial gradient in 2007, with high PM2.5 levels in urban locations and low PM2.5 levels in peri-urban locations gradually weakened by 2013 but re-appeared in 2017. Over the same period, primary PM2.5 emissions declined by 52% from transportation, 15% from industrial and 8% from other anthropogenic sources corresponding to a decrease of 0.8, 0.9 and 0.6 μg/m3 on ambient PM2.5 mass, respectively. Wildland and prescribed fires emissions increased more than three times adding 0.8 μg/m3 to ambient PM2.5 mass. These results indicate that (i) fire emissions may impede the effectiveness of existing policies to improve air quality and (ii) the chemical content of PM2.5 may be changing to an evolving mixture of aromatic and oxygenated organic species with differential toxicological responses as compared to inert ammonium sulfate and nitrate salts. Biomass burning, secondary inorganic (i.e., ammonium sulfate and nitrate) and primary traffic exhausts were the predominant PM2.5 sources. The declining trends of PM2.5 mass in all four sites is were well correlated with decreasing secondary sulfate levels due to SO2 emission reductions by coal-fired power plants. Wintertime biomass burning aerosols were most likely due to combustion of contemporary biomass for industrial and domestic heating, and it was linked to the intensity (average minimum temperature) and duration (number of freezing days) of cold weather. The annual summertime biomass burning contributions were correlated with the number and area burnt by lightning-ignited wildfires.

Conclusions. The spatial and temporal trends of O3 and PM2.5 are changing due to significant reductions on gaseous precursors from anthropogenic sources. As a result, atmospheric chemistry dynamics are modified counteracting emission reduction benefits and, for O3, leading to increasing ambient levels in heavily populated areas that traditionally experienced low O3 due to titration. Moreover, the relative contribution of climate-prone local and regional biomass burning emissions on both O3 and PM2.5 mass concentrations is increasing; thus, altering levels and the chemical content of air pollutants. These findings indicate that climate change may counterbalance current and future gains on emissions controls on anthropogenic activities and modify the biological and toxicological responses and resultant health effects.

Included in

Public Health Commons



To view the content in your browser, please download Adobe Reader or, alternately,
you may Download the file to your hard drive.

NOTE: The latest versions of Adobe Reader do not support viewing PDF files within Firefox on Mac OS and if you are using a modern (Intel) Mac, there is no official plugin for viewing PDF files within the browser window.