Zhuanshi He - Academia.edu (original) (raw)

Papers by Zhuanshi He

Atmospheric Chemistry and Physics, Nov 18, 2022

Daily air concentrations of inorganic nitrogen (N) species, including gaseous HNO 3 and particula... more Daily air concentrations of inorganic nitrogen (N) species, including gaseous HNO 3 and particulatebound (p)NH + 4 and pNO − 3 , and sulfur (S) species, including SO 2 and pSO 2− 4 , and precipitation concentrations of NO − 3 , NH + 4 , and SO 2− 4 , have been routinely monitored by the Canadian Air and Precipitation Monitoring Network (CAPMoN) since 1983. Data at 15 rural sites from 2000-2018 were used to estimate dry and wet N and S deposition fluxes, which were then used to explore their spatiotemporal trends and assess ecosystem damage through a retrospective analysis of critical loads (CLs) exceedances. Total (dry + wet) N deposition ranged from 1.7-9.5 kg N ha −1 yr −1 among the 15 sites, though dry deposition of NH 3 and some oxidized N species were not included due to lack of monitoring data. Based on additional N measurements in 2010 at one of the sites, annual total N deposition may be underestimated by up to 32 %. Total N deposition was dominated by wet NO − 3 and wet NH + 4 deposition, which together comprised 71 %-95 %. Contributions to dry N deposition were 40 %-74 % by HNO 3 , 11 %-40 % by pNH + 4 , and 5 %-25 % by pNO − 3. Total S deposition ranged from 1.3-8.5 kg S ha −1 yr −1 and was dominated by wet deposition of SO 2− 4 and dry deposition of SO 2. Relative percentages of wet and dry S deposition were 45 %-89 % and 11 %-55 %, respectively. Acidic ion fluxes were greatest in southeastern Canada and were comparable among the west coast, prairie, remote, and eastern Canadian sites. Oxidized N (dry HNO 3 , dry pNO − 3 , wet NO − 3) deposition was greater than that of reduced N (dry pNH + 4 , wet NH + 4) in the early 2000s. In 2014-2018, reduced N deposition surpassed that of oxidized N in southeastern Canada. Total N and S deposition decreased significantly at a rate of −0.03 to −0.25 kg N ha −1 yr −1 (−1.1 % yr −1 to −3.3 % yr −1) and −0.08 to −0.66 kg S ha −1 yr −1 (−3.5 % yr −1 to −6.6 % yr −1), respectively, among the sites. The weak declining trend in total N deposition at the west coast site was consistent with the slower decline in NO x emissions in western Canada. Reductions in total N deposition were driven by its oxidized form as trends in reduced N were non-significant. As a result, reduced N contributions to total N deposition increased on average from 42 % in 2000-2004 to 53 % in 2014-2018. Anthropogenic NO x and SO 2 emissions reductions in both eastern Canada and eastern US were highly effective in reducing total oxidized N and total S deposition, respectively, in eastern Canada. Acidic deposition exceeded terrestrial CL at 5 of the 14 sites and aquatic CL at 2 of the 5 sites in the early 2000s. However, exceedances have been trending downwards and acidic deposition fluxes were mostly near or below CL after 2012 for the subset of sites assessed, which support recovery from historical acidification.

S1 Daily average dry deposition velocities (Vd) of N and S species S1.1 Spatial patterns Daily av... more S1 Daily average dry deposition velocities (Vd) of N and S species S1.1 Spatial patterns Daily average Vd for gas-phase compounds (SO2, HNO3) and particulate-phase compounds (pSO4 2-, pNH4 + and pNO3-) for the 2000-2018 period are summarized in Table S2. For gaseous compounds, the mean daily Vd (cm/s) among 15 CAPMoN sites were 1.2 for HNO3 and 0.46 for SO2. For particulate sulfate (pSO4 2-), ammonium (pNH4 +) and nitrate (pNO3-), the mean daily Vd were 0.16, 0.15 and 0.21 cm/s, respectively. Vd of N and S compounds exhibited strong variability between sites. The regions with higher Vd for N and S compounds include the west coast, southeast and Atlantic (Table S2). According to the land use data surrounding a CAPMoN site (Table S1), the west coast and Atlantic sites have higher Vd likely because of nearby land use coverage that is associated with higher Vd. For example, water surfaces and forests. In particular, evergreen needleleaf or broadleaf trees are typically associated with larger leaf area index (LAI) and hence larger Vd. Meteorological conditions also differ substantially across Canadian sites, which can drive the spatial variability in Vd. S1.2 Cold vs. warm seasonal patterns Vd of gaseous N and S compounds were slightly greater in the warm season than cold season at most of the sites based on the monthly variations in Fig. S1. This was also the case for particulate nitrate due to the higher fraction of nitrate in coarse PM during the warm season, which is based on size-fractionated measurements previously conducted at CAPMoN sites (Zhang et al., 2008). Given that Vd of coarse PM (PM2.5-10) is larger than that of fine PM (PM2.5), a higher fraction in coarse PM results in higher Vd. During the cold season, nitrate is predominantly associated with fine PM at CAPMoN sites (Zhang et al., 2008). Vd of sulfate and ammonium were slightly higher in the cold season than warm season. This pattern is likely attributed to meteorology perhaps higher wind speeds in the cold season. S1.3 Long-term annual trends Long-term annual trends in Vd were estimated using Theil-Sen slopes of the seasonal average Vd, which have been seasonally adjusted using LOESS (locally estimated scatterplot smoothing). Statistically significant trends in Vd (p<0.05) are shown in Fig. S2. Among the sites, annual trends in Vd (cm/s of change per year) ranged from 2.

. Daily air concentrations of inorganic nitrogen (N) species, including gaseous HNO3 and particul... more . Daily air concentrations of inorganic nitrogen (N) species, including gaseous HNO3 and particulate-bound (p)NH4+ and pNO3-, and sulfur (S) species, including SO2 and pSO42-, and precipitation concentrations of NO3-, NH4+ and SO42-, have been routinely monitored by the Canadian Air and Precipitation Monitoring Network (CAPMoN) since 1983. Data at 15 rural sites from 2000–2018 were used to estimate dry and wet N and S deposition fluxes, which were then used to explore their spatiotemporal trends and assess ecosystem damage through a retrospective analysis of critical loads (CL) exceedances. Total (dry+wet) N deposition ranged from 1.7–9.5 kg N ha-1 yr-1 among the 15 sites, though dry deposition of NH3 and some oxidized N species were not included due to a lack of data. Based on additional N measurements in 2010 at one of the sites, annual total N deposition may be underestimated by up to 32 %. Total N deposition was dominated by wet NO3- and wet NH4+ deposition, which together comprised 71–95 %. Contributions to dry N deposition were 40–74 % by HNO3, 11–40 % by pNH4+ and 5–25 % by pNO3-. Total S deposition ranged from 1.3–8.5 kg S ha-1 yr-1 and was dominated by wet deposition of SO42- and dry deposition of SO2. Relative percentages of wet and dry S deposition were 45–89 % and 11–55 %, respectively. Acidic ion fluxes were greatest in southeastern Canada and were comparable among the west coast, prairie, remote and eastern Canadian sites. Oxidized N (dry HNO3, dry pNO3-, wet NO3-) deposition was greater than that of reduced N (dry pNH4+, wet NH4+) in the early 2000s. In 2014–2018, reduced N deposition surpassed that of oxidized N in southeastern Canada. Total N and S deposition decreased significantly at a rate of -0.03 to -0.25 kg N ha-1 yr-1 (-1.1 % to -3.3 % yr-1) and -0.08 to -0.66 kg S ha-1 yr-1 (-3.5 % to -6.6 % yr-1), respectively, among the sites. The weak declining trend in total N deposition at the west coast site was consistent with the slower decline in NOx emissions in western Canada. Reductions in total N deposition were driven by its oxidized form as trends in reduced N were non-significant. As a result, reduced N contributions to total N deposition increased on average from 42 % in 2000–2004 to 53 % in 2014–2018. Anthropogenic NOx and SO2 emissions reductions in both eastern Canada and eastern U.S. were highly effective in reducing total oxidized N and total S deposition, respectively, in eastern Canada. Acidic deposition exceeded terrestrial CL at 5 of the 14 sites and aquatic CL at 2 of the 5 sites in the early 2000s. However, exceedances have been trending downwards and acidic deposition fluxes were mostly near or below CL after 2012 for the subset of sites assessed, which support recovery from historical acidification. Further assessments of CL exceedances are required in other Canadian regions susceptible to acidification and affected by elevated or increasing N and S emissions.

Journal of Environmental Sciences

Physicochemical characteristics and radiative properties of Asian dust particles observed at Kwan... more Physicochemical characteristics and radiative properties of Asian dust particles observed at Kwangju, Korea, during the 2001 ACE-Asia

Pollutants such as NO2, which have high spatial and temporal variability in urban areas, yet can ... more Pollutants such as NO2, which have high spatial and temporal variability in urban areas, yet can also be transported for hundreds of kilometers,

Atmospheric Research, May 1, 2008

Aerosol optical properties including Aerosol Optical Depth (AOD, τaλ), Angstrom exponent (α), siz... more Aerosol optical properties including Aerosol Optical Depth (AOD, τaλ), Angstrom exponent (α), size distribution, single scattering albedo (wo) were examined using long-term ground-based radiometric measurements at five West African sites; Dakar (14°42&amp;#39;N 17°29′W), Banizoumbou (13°45′N, 02°39′E), Agoufou (15°21&amp;#39;N,1°29′W), Ilorin (08°32′N, 04°34′E), and Ouagadougou (12°22′N, 1°31′W). Also included were observations made at the Cape Verde Islands (16° 45′N, 22° 57′W) to

Atmospheric and Climate Sciences, 2013

Modeled and measured bi-directional fluxes (BDFs) of ammonia (NH 3) were compared over fertilized... more Modeled and measured bi-directional fluxes (BDFs) of ammonia (NH 3) were compared over fertilized soybean and corn canopies for three intensive sampling periods: the first, during the summer of 2002 in Warsaw, North Carolina (NC), USA; and the second and third during the summer of 2007 in Lillington, NC. For the first and the third experimental periods, the BDF model produced reasonable diurnal flux patterns. The model also produced correct flux directions (emission and dry deposition) and magnitudes under dry and wet canopy conditions and during day and nighttime for these two periods. However, the model fails to produce the observed very high upward fluxes from the second sampling period due to the fertilization application (and thus being much higher soil emission potentials in the field than the default model values), although this can be improved by adjusting model input of soil emission potentials. Model-measurement comparison results suggest that the model is likely capable for improving long-term or regional scale ammonia predictions if implemented in chemical transport models replace the traditional dry deposition models, although modifications are needed when applying to specific situations.

Ultraviolet Ground- and Space-based Measurements, Models, and Effects III, 2003

ABSTRACT Ground-based visible and UV irradiances at 11 wavelengths were measured in order to char... more ABSTRACT Ground-based visible and UV irradiances at 11 wavelengths were measured in order to characterize the wavelength dependence of aerosol optical depth during the biomass burning period (October~November 2002) with a visible/ultraviolet multifilter rotating shadowband radiometer (vis-MFRSR, UV-MFRSR) at Gwangju (35.13°N, 126.53°E), South Korea. UVMFR has 7 wavelengths of 2 nm FWHM centered on, 299, 305, 310, 317, 323, 331, and 367 nm, and vis-MFRSR has 6 channels of 10 nm FWHM on 415, 500, 615, 673, 870 and 930 nm. Measurement outputs from the MFRSRs were sampled at 20 seconds interval and saved every minute as a mean value into a YESDAS data logger. In order to calculate aerosol optical depth at the visible and UV range, total column ozone should be considered because the surface UV radiation, especially UV-B radiation, is highly absorbed by atmospheric ozone. Ozone optical depths were calculated using TOMS (Total ozone mapping spectrometer) daily total column ozone (DU) and WMO (1985) ozone absorption coefficients. Exceptionally, UV radiation at 367.4 nm is free from ozone absorption. Rayleigh optical depth was highly dependent on the wavelength and was calculated using surface pressure information provided by the KMA (Korea Meteorological Administration). This study shows the results on October and November 2002 when both ground-based spectral AOD at visible/UV range and aerosol measurements and chemical analysis were executed simultaneously. AOD varied 0.16 ~ 0.64 dependent on the wavelengths during the measurement period and the AOD values had an anticorrelation with wavelength. On November 12, 2002 both biomass burning and Asian dust were observed simultaneously. The AOD analysis results showed that AOD increased 100~200% dependent on the wavelength when Asian dust and biomass burning were observed compared to the days when no events occurred. Aerosol measurement confirmed this from the increase of mass concentration of aerosol on this date. Aerosol optical parameters were compared with aerosol chemical composition.

Journal of Geophysical Research, 2004

Optical properties of atmospheric extinction, scattering, and absorption coefficients were measur... more Optical properties of atmospheric extinction, scattering, and absorption coefficients were measured continuously with a transmissometer, an integrating nephelometer, and an aethalometer, respectively. Three Asian dust storm events had been observed at Kwangju on 22 March, 11-13 April, and 25-26 April 2001. The physicochemical and optical properties of Asian dust aerosols were analyzed for those three cases and compared with those observed under clean, marine, and hazy urban atmospheric conditions. Their chemical composition varied depending on the source region and the transport path of the air mass. The first Asian dust storm particles, which originated from the northwestern Chinese desert regions, showed typical dust aerosol characteristics of high loading of mineral dust. The second one, which originated initially from the northwestern Chinese desert regions, had been impacted by longrange-transported air pollutants, resulting in increased concentrations of sulfate and organic carbon particles. The third one, which originated from the northeastern Chinese sandy areas, had traveled south to Kwangju, resulting in increased elemental carbon and organic carbon concentrations. Aerosol chemical and optical properties under clean continental, southeastern marine, and stagnant local pollution conditions were also analyzed. The mass scattering coefficient and single-scattering albedo in the fine and coarse modes were determined for three Asian dust event days. The concentration of black carbon (BC) aerosol in the fine and coarse modes was measured with an aethalometer by alternately switching between a particulate-matter-smaller-than-2.5-mm (PM2.5) and a PM10 inlet to it. It was found that BC mass concentration in the coarse mode measured by an aethalometer (BC ac) increased because of agglomerated black carbon particles and high loading of dust particles. Single-scattering albedo w increased to 0.93, 0.90, and 0.84 for the three Asian dust events, respectively, while it was 0.85 for mean w during other times.

Journal of Atmospheric and Solar-Terrestrial Physics, 2006

Simultaneous ground-based measurements of aerosol chemical composition and atmospheric aerosol op... more Simultaneous ground-based measurements of aerosol chemical composition and atmospheric aerosol optical depth (AOD) in the UV and visible regions were carried out at Gwangju (35.13°N, 126.50°E), Korea during a biomass burning period, October 4–November 12, ...

Atmospheric Research, 2006

A UV-MFRSR instrument was used to measure the global and diffuse irradiances in 7 narrowband chan... more A UV-MFRSR instrument was used to measure the global and diffuse irradiances in 7 narrowband channels in the UV range 299.4, 304.4, 310.9, 317.3, 324.5, 331.3 and 367.4 nm at Gwangju (35813V N 126850V E), Korea. Spectral UV-AOD was retrieved using the Langley plot method for data collected from April 2002 to July 2004. Temporal variation of AOD at 367.4 nm (AOD 367 nm) showed a maximum in June (0.95 F 0.43) and a minimum in February (0.31 F 0.14). Clear seasonal variation of AOD 367 nm was observed with average values of 0.68 F 0.29, 0.82 F 0.41, 0.48 F 0.22 and 0.42 F 0.21 in spring, summer, fall and winter, respectively. Average Å ngströ m exponents for the entire monitoring period were 3.35 F 1.06 and 2.03 F 0.75 in the UV (310.9~367.4 nm) and UV-A (324.5~367.4 nm) ranges, respectively. Seasonal variation of the Å ngströ m exponent showed a maximum in spring and a minimum in summer. The lowest Å ngströ m exponent in summer might be due to hygroscopic growth of particles under conditions of high relative humidity. UV-AOD changes under different atmospheric conditions were also analyzed. Longrange transported haze, Asian dust and BB events increased UV-AODs by 2~3 times in comparison to cases involving no events. Uncertainty in retrieving spectral UV-AOD was also estimated to range between F 0.218 at 304.4 nm and F 0.135 at 367.4 nm. Major causes of uncertainty were total column ozone retrieval and extraterrestrial irradiance retrieval at shorter and longer wavelengths, respectively.

cmascenter.org

Pollutants such as NO2, which have high spatial and temporal variability in urban areas, yet can ... more Pollutants such as NO2, which have high spatial and temporal variability in urban areas, yet can also be transported for hundreds of kilometers, are difficult to quantify on all relevant time scales. Their adverse health effects, however, increase the value of a forecasting ...

Advances in Atmospheric Sciences, 1999

, ozone and its precursors were measured in the clean areas of China. The results show that in th... more , ozone and its precursors were measured in the clean areas of China. The results show that in the period of crop growth, hourly mean ozone concentration, ozone concentration averaged in seven hours of daytime and accumulated ozone concentration in long period have approached or overpassed the harmful level in environmental and health standard of U. S. A. and Canada.

Advances in Atmospheric Sciences, 1998

Combining the Penn State/NCAR mesoscale (MM4) model, the dust transport model and an atmospheric ... more Combining the Penn State/NCAR mesoscale (MM4) model, the dust transport model and an atmospheric radiative transfer model, a super duststorm process occurred in the Gansu province on 5 May 1993 has been simulated. Based on the observations of duststorms occurred in the northern China and the field measurements of dust particles' physical and optical properties, model simulating dust plume transport processes and dust particle radiative forcing have been devloped. The models are described and verified with real cases of duststorms.

Advances in Atmospheric Sciences, 1998

Combining the Penn State/NCAR mesoscale (MM4) model, the dust transport model and an atmospheric ... more Combining the Penn State/NCAR mesoscale (MM4) model, the dust transport model and an atmospheric radiative transfer model, a super duststorm process occurred in the Gansu province on 5 May 1993 has been simulated. Based on the observations of duststorms occurred in the northern China and the field measurements of dust particles' physical and optical properties, model simulating dust plume transport processes and dust particle radiative forcing have been devloped. The models are described and verified with real cases of duststorms.

Advances in Atmospheric Sciences, 1998

Combining the Penn State/NCAR mesoscale (MM4) model, the dust transport model and an atmospheric ... more Combining the Penn State/NCAR mesoscale (MM4) model, the dust transport model and an atmospheric radiative transfer model, a super duststorm process occurred in the Gansu province on 5 May 1993 has been simulated. Based on the observations of duststorms occurred in the northern China and the field measurements of dust particles' physical and optical properties, model simulating dust plume transport processes and dust particle radiative forcing have been devloped. The models are described and verified with real cases of duststorms.

Remote Sensing in Atmospheric Pollution Monitoring and Control, 2004

Atmospheric Chemistry and Physics, Nov 18, 2022

Daily air concentrations of inorganic nitrogen (N) species, including gaseous HNO 3 and particula... more Daily air concentrations of inorganic nitrogen (N) species, including gaseous HNO 3 and particulatebound (p)NH + 4 and pNO − 3 , and sulfur (S) species, including SO 2 and pSO 2− 4 , and precipitation concentrations of NO − 3 , NH + 4 , and SO 2− 4 , have been routinely monitored by the Canadian Air and Precipitation Monitoring Network (CAPMoN) since 1983. Data at 15 rural sites from 2000-2018 were used to estimate dry and wet N and S deposition fluxes, which were then used to explore their spatiotemporal trends and assess ecosystem damage through a retrospective analysis of critical loads (CLs) exceedances. Total (dry + wet) N deposition ranged from 1.7-9.5 kg N ha −1 yr −1 among the 15 sites, though dry deposition of NH 3 and some oxidized N species were not included due to lack of monitoring data. Based on additional N measurements in 2010 at one of the sites, annual total N deposition may be underestimated by up to 32 %. Total N deposition was dominated by wet NO − 3 and wet NH + 4 deposition, which together comprised 71 %-95 %. Contributions to dry N deposition were 40 %-74 % by HNO 3 , 11 %-40 % by pNH + 4 , and 5 %-25 % by pNO − 3. Total S deposition ranged from 1.3-8.5 kg S ha −1 yr −1 and was dominated by wet deposition of SO 2− 4 and dry deposition of SO 2. Relative percentages of wet and dry S deposition were 45 %-89 % and 11 %-55 %, respectively. Acidic ion fluxes were greatest in southeastern Canada and were comparable among the west coast, prairie, remote, and eastern Canadian sites. Oxidized N (dry HNO 3 , dry pNO − 3 , wet NO − 3) deposition was greater than that of reduced N (dry pNH + 4 , wet NH + 4) in the early 2000s. In 2014-2018, reduced N deposition surpassed that of oxidized N in southeastern Canada. Total N and S deposition decreased significantly at a rate of −0.03 to −0.25 kg N ha −1 yr −1 (−1.1 % yr −1 to −3.3 % yr −1) and −0.08 to −0.66 kg S ha −1 yr −1 (−3.5 % yr −1 to −6.6 % yr −1), respectively, among the sites. The weak declining trend in total N deposition at the west coast site was consistent with the slower decline in NO x emissions in western Canada. Reductions in total N deposition were driven by its oxidized form as trends in reduced N were non-significant. As a result, reduced N contributions to total N deposition increased on average from 42 % in 2000-2004 to 53 % in 2014-2018. Anthropogenic NO x and SO 2 emissions reductions in both eastern Canada and eastern US were highly effective in reducing total oxidized N and total S deposition, respectively, in eastern Canada. Acidic deposition exceeded terrestrial CL at 5 of the 14 sites and aquatic CL at 2 of the 5 sites in the early 2000s. However, exceedances have been trending downwards and acidic deposition fluxes were mostly near or below CL after 2012 for the subset of sites assessed, which support recovery from historical acidification.

S1 Daily average dry deposition velocities (Vd) of N and S species S1.1 Spatial patterns Daily av... more S1 Daily average dry deposition velocities (Vd) of N and S species S1.1 Spatial patterns Daily average Vd for gas-phase compounds (SO2, HNO3) and particulate-phase compounds (pSO4 2-, pNH4 + and pNO3-) for the 2000-2018 period are summarized in Table S2. For gaseous compounds, the mean daily Vd (cm/s) among 15 CAPMoN sites were 1.2 for HNO3 and 0.46 for SO2. For particulate sulfate (pSO4 2-), ammonium (pNH4 +) and nitrate (pNO3-), the mean daily Vd were 0.16, 0.15 and 0.21 cm/s, respectively. Vd of N and S compounds exhibited strong variability between sites. The regions with higher Vd for N and S compounds include the west coast, southeast and Atlantic (Table S2). According to the land use data surrounding a CAPMoN site (Table S1), the west coast and Atlantic sites have higher Vd likely because of nearby land use coverage that is associated with higher Vd. For example, water surfaces and forests. In particular, evergreen needleleaf or broadleaf trees are typically associated with larger leaf area index (LAI) and hence larger Vd. Meteorological conditions also differ substantially across Canadian sites, which can drive the spatial variability in Vd. S1.2 Cold vs. warm seasonal patterns Vd of gaseous N and S compounds were slightly greater in the warm season than cold season at most of the sites based on the monthly variations in Fig. S1. This was also the case for particulate nitrate due to the higher fraction of nitrate in coarse PM during the warm season, which is based on size-fractionated measurements previously conducted at CAPMoN sites (Zhang et al., 2008). Given that Vd of coarse PM (PM2.5-10) is larger than that of fine PM (PM2.5), a higher fraction in coarse PM results in higher Vd. During the cold season, nitrate is predominantly associated with fine PM at CAPMoN sites (Zhang et al., 2008). Vd of sulfate and ammonium were slightly higher in the cold season than warm season. This pattern is likely attributed to meteorology perhaps higher wind speeds in the cold season. S1.3 Long-term annual trends Long-term annual trends in Vd were estimated using Theil-Sen slopes of the seasonal average Vd, which have been seasonally adjusted using LOESS (locally estimated scatterplot smoothing). Statistically significant trends in Vd (p<0.05) are shown in Fig. S2. Among the sites, annual trends in Vd (cm/s of change per year) ranged from 2.

. Daily air concentrations of inorganic nitrogen (N) species, including gaseous HNO3 and particul... more . Daily air concentrations of inorganic nitrogen (N) species, including gaseous HNO3 and particulate-bound (p)NH4+ and pNO3-, and sulfur (S) species, including SO2 and pSO42-, and precipitation concentrations of NO3-, NH4+ and SO42-, have been routinely monitored by the Canadian Air and Precipitation Monitoring Network (CAPMoN) since 1983. Data at 15 rural sites from 2000–2018 were used to estimate dry and wet N and S deposition fluxes, which were then used to explore their spatiotemporal trends and assess ecosystem damage through a retrospective analysis of critical loads (CL) exceedances. Total (dry+wet) N deposition ranged from 1.7–9.5 kg N ha-1 yr-1 among the 15 sites, though dry deposition of NH3 and some oxidized N species were not included due to a lack of data. Based on additional N measurements in 2010 at one of the sites, annual total N deposition may be underestimated by up to 32 %. Total N deposition was dominated by wet NO3- and wet NH4+ deposition, which together comprised 71–95 %. Contributions to dry N deposition were 40–74 % by HNO3, 11–40 % by pNH4+ and 5–25 % by pNO3-. Total S deposition ranged from 1.3–8.5 kg S ha-1 yr-1 and was dominated by wet deposition of SO42- and dry deposition of SO2. Relative percentages of wet and dry S deposition were 45–89 % and 11–55 %, respectively. Acidic ion fluxes were greatest in southeastern Canada and were comparable among the west coast, prairie, remote and eastern Canadian sites. Oxidized N (dry HNO3, dry pNO3-, wet NO3-) deposition was greater than that of reduced N (dry pNH4+, wet NH4+) in the early 2000s. In 2014–2018, reduced N deposition surpassed that of oxidized N in southeastern Canada. Total N and S deposition decreased significantly at a rate of -0.03 to -0.25 kg N ha-1 yr-1 (-1.1 % to -3.3 % yr-1) and -0.08 to -0.66 kg S ha-1 yr-1 (-3.5 % to -6.6 % yr-1), respectively, among the sites. The weak declining trend in total N deposition at the west coast site was consistent with the slower decline in NOx emissions in western Canada. Reductions in total N deposition were driven by its oxidized form as trends in reduced N were non-significant. As a result, reduced N contributions to total N deposition increased on average from 42 % in 2000–2004 to 53 % in 2014–2018. Anthropogenic NOx and SO2 emissions reductions in both eastern Canada and eastern U.S. were highly effective in reducing total oxidized N and total S deposition, respectively, in eastern Canada. Acidic deposition exceeded terrestrial CL at 5 of the 14 sites and aquatic CL at 2 of the 5 sites in the early 2000s. However, exceedances have been trending downwards and acidic deposition fluxes were mostly near or below CL after 2012 for the subset of sites assessed, which support recovery from historical acidification. Further assessments of CL exceedances are required in other Canadian regions susceptible to acidification and affected by elevated or increasing N and S emissions.

Journal of Environmental Sciences

Physicochemical characteristics and radiative properties of Asian dust particles observed at Kwan... more Physicochemical characteristics and radiative properties of Asian dust particles observed at Kwangju, Korea, during the 2001 ACE-Asia

Pollutants such as NO2, which have high spatial and temporal variability in urban areas, yet can ... more Pollutants such as NO2, which have high spatial and temporal variability in urban areas, yet can also be transported for hundreds of kilometers,

Atmospheric Research, May 1, 2008

Aerosol optical properties including Aerosol Optical Depth (AOD, τaλ), Angstrom exponent (α), siz... more Aerosol optical properties including Aerosol Optical Depth (AOD, τaλ), Angstrom exponent (α), size distribution, single scattering albedo (wo) were examined using long-term ground-based radiometric measurements at five West African sites; Dakar (14°42&amp;#39;N 17°29′W), Banizoumbou (13°45′N, 02°39′E), Agoufou (15°21&amp;#39;N,1°29′W), Ilorin (08°32′N, 04°34′E), and Ouagadougou (12°22′N, 1°31′W). Also included were observations made at the Cape Verde Islands (16° 45′N, 22° 57′W) to

Atmospheric and Climate Sciences, 2013

Modeled and measured bi-directional fluxes (BDFs) of ammonia (NH 3) were compared over fertilized... more Modeled and measured bi-directional fluxes (BDFs) of ammonia (NH 3) were compared over fertilized soybean and corn canopies for three intensive sampling periods: the first, during the summer of 2002 in Warsaw, North Carolina (NC), USA; and the second and third during the summer of 2007 in Lillington, NC. For the first and the third experimental periods, the BDF model produced reasonable diurnal flux patterns. The model also produced correct flux directions (emission and dry deposition) and magnitudes under dry and wet canopy conditions and during day and nighttime for these two periods. However, the model fails to produce the observed very high upward fluxes from the second sampling period due to the fertilization application (and thus being much higher soil emission potentials in the field than the default model values), although this can be improved by adjusting model input of soil emission potentials. Model-measurement comparison results suggest that the model is likely capable for improving long-term or regional scale ammonia predictions if implemented in chemical transport models replace the traditional dry deposition models, although modifications are needed when applying to specific situations.

Ultraviolet Ground- and Space-based Measurements, Models, and Effects III, 2003

ABSTRACT Ground-based visible and UV irradiances at 11 wavelengths were measured in order to char... more ABSTRACT Ground-based visible and UV irradiances at 11 wavelengths were measured in order to characterize the wavelength dependence of aerosol optical depth during the biomass burning period (October~November 2002) with a visible/ultraviolet multifilter rotating shadowband radiometer (vis-MFRSR, UV-MFRSR) at Gwangju (35.13°N, 126.53°E), South Korea. UVMFR has 7 wavelengths of 2 nm FWHM centered on, 299, 305, 310, 317, 323, 331, and 367 nm, and vis-MFRSR has 6 channels of 10 nm FWHM on 415, 500, 615, 673, 870 and 930 nm. Measurement outputs from the MFRSRs were sampled at 20 seconds interval and saved every minute as a mean value into a YESDAS data logger. In order to calculate aerosol optical depth at the visible and UV range, total column ozone should be considered because the surface UV radiation, especially UV-B radiation, is highly absorbed by atmospheric ozone. Ozone optical depths were calculated using TOMS (Total ozone mapping spectrometer) daily total column ozone (DU) and WMO (1985) ozone absorption coefficients. Exceptionally, UV radiation at 367.4 nm is free from ozone absorption. Rayleigh optical depth was highly dependent on the wavelength and was calculated using surface pressure information provided by the KMA (Korea Meteorological Administration). This study shows the results on October and November 2002 when both ground-based spectral AOD at visible/UV range and aerosol measurements and chemical analysis were executed simultaneously. AOD varied 0.16 ~ 0.64 dependent on the wavelengths during the measurement period and the AOD values had an anticorrelation with wavelength. On November 12, 2002 both biomass burning and Asian dust were observed simultaneously. The AOD analysis results showed that AOD increased 100~200% dependent on the wavelength when Asian dust and biomass burning were observed compared to the days when no events occurred. Aerosol measurement confirmed this from the increase of mass concentration of aerosol on this date. Aerosol optical parameters were compared with aerosol chemical composition.

Journal of Geophysical Research, 2004

Optical properties of atmospheric extinction, scattering, and absorption coefficients were measur... more Optical properties of atmospheric extinction, scattering, and absorption coefficients were measured continuously with a transmissometer, an integrating nephelometer, and an aethalometer, respectively. Three Asian dust storm events had been observed at Kwangju on 22 March, 11-13 April, and 25-26 April 2001. The physicochemical and optical properties of Asian dust aerosols were analyzed for those three cases and compared with those observed under clean, marine, and hazy urban atmospheric conditions. Their chemical composition varied depending on the source region and the transport path of the air mass. The first Asian dust storm particles, which originated from the northwestern Chinese desert regions, showed typical dust aerosol characteristics of high loading of mineral dust. The second one, which originated initially from the northwestern Chinese desert regions, had been impacted by longrange-transported air pollutants, resulting in increased concentrations of sulfate and organic carbon particles. The third one, which originated from the northeastern Chinese sandy areas, had traveled south to Kwangju, resulting in increased elemental carbon and organic carbon concentrations. Aerosol chemical and optical properties under clean continental, southeastern marine, and stagnant local pollution conditions were also analyzed. The mass scattering coefficient and single-scattering albedo in the fine and coarse modes were determined for three Asian dust event days. The concentration of black carbon (BC) aerosol in the fine and coarse modes was measured with an aethalometer by alternately switching between a particulate-matter-smaller-than-2.5-mm (PM2.5) and a PM10 inlet to it. It was found that BC mass concentration in the coarse mode measured by an aethalometer (BC ac) increased because of agglomerated black carbon particles and high loading of dust particles. Single-scattering albedo w increased to 0.93, 0.90, and 0.84 for the three Asian dust events, respectively, while it was 0.85 for mean w during other times.

Journal of Atmospheric and Solar-Terrestrial Physics, 2006

Simultaneous ground-based measurements of aerosol chemical composition and atmospheric aerosol op... more Simultaneous ground-based measurements of aerosol chemical composition and atmospheric aerosol optical depth (AOD) in the UV and visible regions were carried out at Gwangju (35.13°N, 126.50°E), Korea during a biomass burning period, October 4–November 12, ...

Atmospheric Research, 2006

A UV-MFRSR instrument was used to measure the global and diffuse irradiances in 7 narrowband chan... more A UV-MFRSR instrument was used to measure the global and diffuse irradiances in 7 narrowband channels in the UV range 299.4, 304.4, 310.9, 317.3, 324.5, 331.3 and 367.4 nm at Gwangju (35813V N 126850V E), Korea. Spectral UV-AOD was retrieved using the Langley plot method for data collected from April 2002 to July 2004. Temporal variation of AOD at 367.4 nm (AOD 367 nm) showed a maximum in June (0.95 F 0.43) and a minimum in February (0.31 F 0.14). Clear seasonal variation of AOD 367 nm was observed with average values of 0.68 F 0.29, 0.82 F 0.41, 0.48 F 0.22 and 0.42 F 0.21 in spring, summer, fall and winter, respectively. Average Å ngströ m exponents for the entire monitoring period were 3.35 F 1.06 and 2.03 F 0.75 in the UV (310.9~367.4 nm) and UV-A (324.5~367.4 nm) ranges, respectively. Seasonal variation of the Å ngströ m exponent showed a maximum in spring and a minimum in summer. The lowest Å ngströ m exponent in summer might be due to hygroscopic growth of particles under conditions of high relative humidity. UV-AOD changes under different atmospheric conditions were also analyzed. Longrange transported haze, Asian dust and BB events increased UV-AODs by 2~3 times in comparison to cases involving no events. Uncertainty in retrieving spectral UV-AOD was also estimated to range between F 0.218 at 304.4 nm and F 0.135 at 367.4 nm. Major causes of uncertainty were total column ozone retrieval and extraterrestrial irradiance retrieval at shorter and longer wavelengths, respectively.

cmascenter.org

Pollutants such as NO2, which have high spatial and temporal variability in urban areas, yet can ... more Pollutants such as NO2, which have high spatial and temporal variability in urban areas, yet can also be transported for hundreds of kilometers, are difficult to quantify on all relevant time scales. Their adverse health effects, however, increase the value of a forecasting ...

Advances in Atmospheric Sciences, 1999

, ozone and its precursors were measured in the clean areas of China. The results show that in th... more , ozone and its precursors were measured in the clean areas of China. The results show that in the period of crop growth, hourly mean ozone concentration, ozone concentration averaged in seven hours of daytime and accumulated ozone concentration in long period have approached or overpassed the harmful level in environmental and health standard of U. S. A. and Canada.

Advances in Atmospheric Sciences, 1998

Combining the Penn State/NCAR mesoscale (MM4) model, the dust transport model and an atmospheric ... more Combining the Penn State/NCAR mesoscale (MM4) model, the dust transport model and an atmospheric radiative transfer model, a super duststorm process occurred in the Gansu province on 5 May 1993 has been simulated. Based on the observations of duststorms occurred in the northern China and the field measurements of dust particles' physical and optical properties, model simulating dust plume transport processes and dust particle radiative forcing have been devloped. The models are described and verified with real cases of duststorms.

Advances in Atmospheric Sciences, 1998

Combining the Penn State/NCAR mesoscale (MM4) model, the dust transport model and an atmospheric ... more Combining the Penn State/NCAR mesoscale (MM4) model, the dust transport model and an atmospheric radiative transfer model, a super duststorm process occurred in the Gansu province on 5 May 1993 has been simulated. Based on the observations of duststorms occurred in the northern China and the field measurements of dust particles' physical and optical properties, model simulating dust plume transport processes and dust particle radiative forcing have been devloped. The models are described and verified with real cases of duststorms.

Advances in Atmospheric Sciences, 1998

Combining the Penn State/NCAR mesoscale (MM4) model, the dust transport model and an atmospheric ... more Combining the Penn State/NCAR mesoscale (MM4) model, the dust transport model and an atmospheric radiative transfer model, a super duststorm process occurred in the Gansu province on 5 May 1993 has been simulated. Based on the observations of duststorms occurred in the northern China and the field measurements of dust particles' physical and optical properties, model simulating dust plume transport processes and dust particle radiative forcing have been devloped. The models are described and verified with real cases of duststorms.

Remote Sensing in Atmospheric Pollution Monitoring and Control, 2004