Identifying sources of ozone to three rural locations in Nevada, USA, using ancillary gas pollutants, aerosol chemistry, and mercury

Atmospheric reactive mercury concentrations in coastal Australia and the Southern Ocean

Mercury (Hg), especially reactive Hg (RM), data from the Southern Hemisphere (SH) are limited. In this study, long-term measurements of both gaseous elemental Hg (GEM) and RM were made at two ground-based monitoring locations in Australia, the Cape Grim Baseline Air Pollution Station (CGBAPS) in Tasmania, and the Macquarie University Automatic Weather Station (MQAWS) in Sydney, New South Wales. Measurements were also made on board the Australian RV Investigator (RVI) during an ocean research voyage to the East Antarctic coast. GEM was measured using the standard Tekran® 2537 series analytical platform, and RM was measured using cation exchange membranes (CEM) in a filter-based sampling method. Overall mean RM concentrations at CGBAPS and MQAWS were 15.9 ± 6.7 pg m^-3 and 17.8 ± 6.6 pg m^-3, respectively. For the 10-week austral summer period on RVI, mean RM was 23.5 ± 6.7 pg m^-3. RM concentrations at CGBAPS were seasonally invariable, while those at MQAWS were significantly different between summer and winter due to seasonal changes in synoptic wind patterns. During the RVI voyage, RM concentrations were relatively enhanced along the Antarctic coast (up to 30 pg m^-3) and GEM concentrations were variable (0.2 to 0.9 ng m^-3), suggesting periods of enrichment and depletion. Both RM and GEM concentrations were relatively lower while transiting the Southern Ocean farther north of Antarctica. RM concentrations measured in this study were higher in comparison to most other reported measurements of RM in the global marine boundary layer (MBL), especially for remote SH locations. As observations of GEM and RM concentrations inform global ocean-atmosphere model simulations of the atmospheric Hg budget, our results have important implications for understanding of total atmospheric Hg (TAM).

Verification of satellite ozone/temperature profile products and ozone effective height/temperature over Kunming, China

Ozonesonde data from November 2013 to April 2015 over Kunming, China are used to verify ozone and temperature profile retrievals from two spaceborne instruments, the version 4.2 product from the Microwave Limb Sounder (MLS) on the NASA Aura satellite and the version 6.0 product from the Atmospheric Infrared Sounder (AIRS) on the NASA Aqua satellite. We calculated and compared the ozone effective height H_eff and effective temperature T_eff, which are two important parameters in ground-based total ozone retrieval through the use of various profile datasets. This is used to verify the accuracy of the operative values (H_eff(0) = 23 km, T_eff(0) = -46.3 °C (or -45 °C)) from the World Meteorological Organization. The results show that the deviation of MLS and AIRS ozone profiles from ozone sounding data has significant oscillation and scatter in the upper troposphere and lower stratosphere. The average difference of MLS at 82.5 hPa is (80.5 ± 65.1) %, and that of AIRS at 70 and 100 hPa are (105.6 ± 74.9) % and (107.0 ± 67.8) %, respectively. The two satellite temperature profiles have differences within ±3 °C and can effectively describe the vertical distribution and variation of temperature. When calculating the H_eff and T_eff, upper stratospheric data missing from the sounding data must be filled in by the satellite profile data; otherwise the calculated results will show large errors of 3.2 km and 3.3 °C. The H_eff and T_eff at Kunming are respectively 24.36 to 25.51 km and -48.3 to -43.6 °C. The operational H_eff and T_eff used at Kunming ozone observation station clearly do not conform to the actual situation and must be corrected.

Transport paths and vertical exchange characteristics of haze pollution in Southern China

Transport paths and vertical exchange characteristics are important factors for understanding the long-term transport, dispersion capability for haze prediction. Many previous studies revealed that the Pearl River Delta (PRD) region, one of the major polluted areas in China, is largely affected by the long-range pollution transport. However, mostly of these studies focused on the source apportionment or horizontal transport path of pollutants by using short-term data, and the vertical exchange characteristics had been rarely analyzed. In this study, using HYSPLIT model, the transport paths and the vertical exchange characteristics of haze episodes over four sub-region of Guangdong (GD) Province in southern China of dry season and wet season were analyzed by using 10years data from 2005 to 2014. Three major transport paths can be statistically summarized based on the long-term data. The haze episodes in PRD and North-GD were distinguished by the characteristics of high frequency and long duration, while the West-GD and East-GD are relatively clean. The haze over North-GD and PRD were mainly influenced by the airflows from northern path, which could bring the pollution from Jiangxi, Anhui, and also influenced by the airflows from coastal path, which could bring the pollution of eastern coastal from Zhejiang and Fujian to Guangdong, while regional transport contributions from Guangdong province and adjacent areas can also be clearly observed. The haze pollution from the identified two major transport paths were mainly transported within the mixing layer (>80% trajectories, <500m), whereas the probability of haze trajectories across mixing layer was relatively low and generally associated with much longer transport distance and higher terrain height over Western China. Combing the vertical exchange analysis, results also show that Wuyi Mountains and Nanling Mountains played a role as barrier to obstruct the haze airflows from other regions of China to the Guangdong province.

Use of multiple tools including lead isotopes to decipher sources of ozone and reactive mercury to urban and rural locations in Nevada, USA

Ambient air particulate matter (<2.5μm in diameter) samples were collected on two different filter types in 2014 and 2015 over 24h periods and analyzed for reactive mercury (gaseous oxidized mercury+particulate bound mercury) concentrations and lead isotopes to determine sources of pollution to three sites in Nevada, USA. Two sites were located on the western edge of Nevada (Reno, urban, 1370m and Peavine Peak, rural, high elevation, 2515m); the third location was ~485km east in rural Great Basin National Park, NV (2061m). Reactive mercury samples were collected on cation exchange membranes simultaneously with lead samples, collected on Teflon membranes. Lead isotopic ratios have previously identified trans-Pacific lead sources based on the 206/207 and 208/207 lead ratios. Influence from trans-Pacific air masses was higher from March to June associated with long-range transport of pollutants. Spring months are well known for increased transport across the Pacific; however, fall months were also influenced by trans-Pacific air masses in this study. Western North American background ozone concentrations have been measured and modeled at 50 to 55ppbv. Median ozone concentrations at both rural sites in Nevada were within this range. Sources leading to enhancements in ozone of 2 to 18ppbv above monthly medians in Nevada included emissions from Eurasia, regional urban centers, and global and regional wildfires, resulting in concentrations close to the USA air quality standard. At the high elevation locations, ozone was derived from pollutants being transported in the free troposphere that originate around the globe; however, Eurasia and Asia were dominant sources to the Western USA. Negative correlations between reactive mercury and percent Asian lead, Northern Eurasia and East Asia trajectories indicated reactive mercury concentrations at the two high elevation sites were produced by oxidants from local, regional, and marine boundary layer sources.

Surface ozone levels in the forest and vegetation areas of the Biga Peninsula, Turkey

Spatial and temporal variability of surface ozone in the rural, mountainous and suburban sites of Biga Peninsula, at the northwest of Turkey which is about 300km southwest of Istanbul was investigated using passive samplers and continuous analyzers. A total 10 passive samplers and two continuous analyzers were used between 1.1.2013 and 31.12.2014. OX levels in the study region were examined to understand NOx dependent or independent contribution to ozone. The influences of the meteorological parameters on ozone levels were also examined by wind speed and ambient temperature. The results clearly show that mountainous areas have higher cumulative exposure to ozone than suburban locations. In order to understand the long range transport sources contributing to the high ozone levels in the region backward trajectories were computed using HYSPLIT model and then clustering of trajectories are performed. The results clearly show the characteristics of pollutant transport from north to Biga Peninsula. Additionally, AOT40 (Accumulated hourly O3 concentrations Over a Threshold of 40ppb) cumulative index was calculated using daytime hourly measurements. The results indicate that the ozone values in the study area are much higher than the critical levels for forest and vegetation based on EU Directive 2008/50/EC.

Development of a statistical model to identify spatial and meteorological drivers of elevated O3 in Nevada and its application to other rural mountainous regions

Measurements of O3 at relatively remote monitoring sites are useful for quantifying baseline O3, and subsequently the magnitude of O3 not controllable by local regulations. As the National Ambient Air Quality Standard (NAAQS) for O3 becomes more stringent, there is an increased need to quantify baseline O3 particularly in the Western US, where regional and global sources can significantly enhance O3 measured at surface sites, yielding baseline mixing ratios approaching or exceeding the NAAQS threshold. Past work has indicated that meteorological conditions as well as site specific spatial characteristics (e.g. elevation, basin size, gradient) are significantly correlated with O3 intercepted at rural monitoring sites. Here, we use 3 years of measurements from sites throughout rural Nevada to develop a categorical tree model to identify spatial and meteorological characteristics that are associated with elevated baseline O3. Data from other sites in the Intermountain Western US are used to test the applicability of the model for sites throughout the region. Our analyses indicate that increased elevation and basin size were associated with increased frequency of elevated O3. On a daily time scale, relative humidity had the strongest association with observed MDA8 O3. Seventy-four percent of MDA8 O3 observations>60 ppbv occurred when daily minimum relative humidity was <15%. Further, we found that including ancillary pollutant data did not improve the predictive accuracy for measurements >60 ppbv whereas including upper air meteorological measurements improved the accuracy of predicting periods when O3 was >60 ppbv. These findings indicate that transport, rather than local production, influences O3 measurements in Nevada, and that high elevation sites in rural Nevada, are representative of baseline conditions in the Intermountain Western US.