Jason Blake Cohen

Aerosol Growth in a Steady-State, Continuous Flow Chamber: Application to Studies of Secondary Aerosol Formation

An analytical solution for the steady-state aerosol size distribution achieved in a steady-state, continuous flow chamber is derived, where particle growth is occurring by gas-to-particle conversion and particle loss is occurring by deposition to the walls of the chamber. The solution is presented in the case of two condensing species. By fitting the predicted steady-state aerosol size distribution to that measured, one may infer information about the nature of the condensing species from the calculated values of the speciess molecular weights. The analytical solution is applied to three sets of experiments on secondary organic aerosol formation carried out in the U.S. Environmental Protection Agency irradiated continuous flow reactor, with parent hydrocarbons: toluene, f -pinene, and a mixture of toluene and f -pinene. Fits to the observed size distributions are illustrated by assuming two condensing products for each parent hydrocarbon; this is a highly simplified picture of secondary organic aerosol formation, which is known to involve considerably more than two condensing products. While not based on a molecular-level model of the gas-to-particle conversion process, the model does allow one to evaluate the extent to which the observed size distribution agrees with that based on a simple, two-component picture of condensation, and to study the sensitivity of those size distributions to variation of the essential properties of the condensing compounds, such as molecular weight. An inherent limitation of the steady-state experiment is that it is not possible to calculate the vapor pressures of the condensing species.

Quantifying the occurrence and magnitude of the Southeast Asian fire climatology

Current emissions inventories of black carbon aerosol, an important component of PM2.5 and a powerful climate altering species, are highly uncertain in both space and time. One of the major and hardest to constrain sources of black carbon is fire, which comes from a combination of forest, vegetation, agricultural, and peat sources. Therefore, quantifying this source more precisely in both space and time is essential. While there is a growing body of work on this topic, the best estimations generally underestimate measurements by integer factors. In this work, 12 years of measurements from 2000 through 2012 of AOD from the MISR satellite and AOD and AAOD from the AERONET network, are used to evaluate the aerosol climatology from Southeast Asian fires. First, the fires in Southeast Asia are uniquely characterized in both space and time to reveal two major burning regions: one with a regular inter-annual and intra-annual distribution, and the other with an irregular inter-annual and somewhat variable intra-annual distribution. These patterns correspond well with regional and local measurements of both composition and meteorology. Using these newly developed relationships, a new temporally and spatially varying set of black carbon emissions is developed. Finally, the best fits with the various measurements yield an annual average value for black carbon emissions due to fires bounded by the range 0.36?0.54 Tg yr?1, with the amount in the year of the greatest fires being bounded by the range 1.2?1.8 Tg yr?1. These magnitudes are significantly higher and differently distributed in space and time when compared with current inventories, and therefore are expected to have a significant impact on regional particulate loadings and the global climate system.

High time-resolved elemental components in fine and coarse particles in the Pearl River Delta region of Southern China: Dynamic variations and effects of meteorology.

Hourly-resolved PM2.5 and PM10-2.5 samples were collected in the industrial city Foshan in the Pearl River Delta region, China. The samples were subsequently analyzed for elemental components and black carbon (BC). A key purpose of the study was to understand the composition of particulate matter (PM) at high-time resolution in a polluted urban atmosphere to identify key components contributing to extreme PM concentration events and examine the diurnal chemical concentration patterns for air quality management purposes. It was found that BC and S concentrations dominated in the fine mode, while elements with mostly crustal and oceanic origins such as Si, Ca, Al and Cl were found in the coarse size fraction. Most of the elements showed strong diurnal variations. S did not show clear diurnal variations, suggesting regional rather than local origin. Based on empirical orthogonal functions (EOF) method, 3 forcing factors were identified contributing to the extreme events of PM2.5 and selected elements, i.e., urban direct emissions, wet deposition and a combination of coarse mode sources. Conditional probability functions (CPF) were performed using wind profiles and elemental concentrations. The CPF results showed that BC and elemental Cl, K, Fe, Cu and Zn in the fine mode were mostly from the northwest, indicating that industrial emissions and combustion were the main sources. For elements in the coarse mode, Si, Al, K, Ca, Fe and Ti showed similar patterns, suggesting same sources such as local soil dust/construction activities. Coarse elemental Cl was mostly from the south and southeast, implying the influence of marine aerosol sources. For other trace elements, we found vanadium (V) in fine PM was mainly from the sources located to the southeast of the measuring site. Combined with CPF results of S and V in fine PM, we concluded shipping emissions were likely an important elemental emission source.

Impact of Urbanization on Regional Climate and Air Quality in China

China has experienced rapid urbanization and economic development during the past 30 years. Changes in land use and land cover (LULC) alter the exchange of energy, momentum, moisture, and trace gases within the vegetation-soil-atmosphere continuum, which in turn affects local and regional circulation and climate, and consequently the dispersion of pollutants and air quality. In this chapter, the integrated WRF/Chem-urban modelling system is described. The urban canopy schemes are tested under different weather conditions and the optimized scheme is obtained in China. The trend of urbanization in China is clarified including land use change, GDP, energy consumption and emissions variations. We present the study on the connections among land cover change, regional climate and air quality. The Pearl River Delta (PRD) and Yangtze River Delta (YRD) Economic Belts were chosen as an example to quantitatively investigate the regional climate and air quality change due to urbanization.