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Dry particulate nitrate deposition in China Lei Liu, Xiuying Zhang, Yan Zhang, Wen xU, Xuejun Liu, Xiaoming Zhang, Junlan Feng, Xinrui Chen, Yuehan Zhang, Xuehe Lu, Shanqian Wang, Wuting Zhang, and Limin Zhao Environ. Sci. Technol., Just Accepted Manuscript • Publication Date (Web): 20 Apr 2017 Downloaded from http://pubs.acs.org on April 20, 2017
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Dry Particulate Nitrate Deposition in China
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Lei Liu a, Xiuying Zhang
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Xinrui Chen b, Yuehan Zhang e, Xuehe Lu a, Shanqian Wang a, Wuting Zhang a, Limin Zhao a
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a
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Institute for Earth System Science, Nanjing University, Nanjing, 210023, China
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b
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University, Shanghai, 200433, China.
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c
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Key Lab of Plant-Soil Interactions of MOE, China Agricultural University, Beijing, 100193, China
a, *
, Yan Zhang b, Wen Xu c, Xuejun Liu c, Xiaomin Zhang a, d, Junlan Feng b,
Jiangsu Provincial Key Laboratory of Geographic Information Science and Technology, International
Center for Atmospheric Chemistry Study, Department of Environmental Science and Engineering, Fudan
College of Resources and Environmental Sciences, Centre for Resources, Environment and Food Security,
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d
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Application, Nanjing, 210023, China
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e
Jiangsu Center for Collaborative Innovation in Geographical Information Resource Development and
School of Atmospheric Sciences, Nanjing University, Nanjing, 200433, China
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* Corresponding author: Xiuying Zhang, Email:
[email protected] 15
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ABSTRACT
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A limited number of ground measurements of dry particulate nitrate deposition (NO3-) makes it difficult
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and challenging to fully know the status of the spatial and temporal variations of dry NO3- depositions over
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China. This study tries to expand the ground measurements of NO3- concentrations at monitoring sites to a
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national scale, based on the Ozone Monitoring Instrument (OMI) NO2 columns, NO2 profiles from an
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atmospheric chemistry transport model (Model for Ozone and Related chemical Tracers, version 4,
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MOZART-4) and monitor-based sources, and then estimates the NO3- depositions on a regional scale based
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on an inferred model. The ground NO2 concentrations were firstly derived from NO2 columns and the NO2
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profiles, and then the ground NO3- concentrations were derived from the ground NO2 concentrations and
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the relationship between NO2 and NO3- based on Chinese Nationwide Nitrogen Deposition Monitoring
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Network (NNDMN). This estimated dry NO3- depositions over China will be helpful in determining the
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magnitude and pollution status in regions without ground measurements, supporting the construction plan
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of environmental monitoring in future.
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TOC GRAPHIC
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INTRODUCTION
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The global nitrogen (N) cycle has been accelerated by intense anthropogenic activity through cultivation of
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combustion of fossil fuel, the Haber-Bosch process and N-fixing legumes
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+ NO2) are emitted into the atmosphere, transformed by chemical reactions, and finally deposited in soil,
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vegetation and water 3. Enhanced N deposition may pose a great influence on ecosystems, including
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changes in species composition, biodiversity reduction, and impairment of air and water quality through
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atmospheric deposition
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essential source, and ground measurements of NO3- are needed in order to get better knowledge of spatial
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patterns and the magnitude of N inputs.
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Direct measurements of NO3- dry depositions can be used by techniques such as dynamic chambers
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eddy correlation 8. In actuality, direct measurements are relatively rare, and indirect measurements (e.g.,
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gradient analysis, inferential) can be made to estimate dry deposition. The inferential method has been
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widely applied
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deposition velocity. To quantify dry NO3- depositions at the regional scale, long-term monitoring networks
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such as NNDMN (Chinese Nationwide Nitrogen Deposition Monitoring Network), EANET (Acid
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Deposition Monitoring Network in East Asia), EMEP (European Monitoring and Evaluation Programme,
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Europe), CASTNET/NADP (Clean Air Status and Trends Network/the National Atmospheric Deposition
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Program, United States) and CAPMoN (Canadian Air and Precipitation Monitoring Network, Canada),
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have been established. However, it is still difficult to understand the status of the dry NO3- depositions on a
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regional scale due to the limited numbers of monitoring sites, biases from site locations far from emission
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sources and the sparse coverage. An alternative method uses a global or regional model to generate maps of
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dry NO3- depositions, and then uses the ground measurements to validate those results.
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To obtain the dry NO3- deposition on a regional scale, this study tried to expand the ground dry NO3-
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deposition with the aid of satellite data
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columns in atmosphere with a high spatial and temporal resolutions since 1990s, which might be useful in
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the estimation of NO3- depositions. Among the present nadir-viewing instruments in orbit available to
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measure NO2, the Ozone Monitoring Instrument (OMI) mounted on the Aura satellite provides the best
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horizontal resolution (13×24 km2 at nadir) with global coverage. Although several studies have shown that
3, 9-11
4-6
1, 2
. Nitrogen oxides (NOx = NO
. Particulate dry nitrate depositions (NO3-) deposited to the Earth are also an
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or
, which uses measured ground NO3- concentrations in combination with modeled dry
12-14
. The remotely sensed technique could estimate the NO2
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the NO2 columns could be used to calculate the gaseous NO2 deposition 3, 12, 13, it is still difficult to estimate
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dry NO3- depositions using the NO2 columns because whether the dry NO3- concentration can be derived
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from the NO2 columns is still unknown. To our knowledge, there was only one study 14 using an inferential
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model to estimate the NO3- deposition on a regional scale based on the estimated NO3- concentrations from
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NO2 columns, and researchers concluded that the dry NO3- depositions over China were 0.07 kg N ha-1 y-1.
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However, this average was much lower than the lowest ground measurements in NNDMN sites (0.10-4.5
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kg N ha-1 y-1, with an average of 1.5 kg N ha-1 y-1) 9. The reason for the big gap between the estimated NO3-
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deposition in Jia et al. (2016)
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could be that Jia et al. (2016)
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columns to estimate the NO3- in particulate matters, which might introduced a high uncertainty in the
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estimated NO3- deposition over China, since the NO3- concentrations have no direct relationship with the
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NO2 columns. To enhance the method of estimating NO3- deposition, it may be more appropriate to derive
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the NO3- concentrations regressed with ground NO2 concentrations, rather than the NO2 columns mainly
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because the ground-level NO3- concentrations were greatly influenced by the ground NO2 concentrations 9,
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10
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We aim to estimate dry NO3- depositions from the remotely sensed NO2 columns and MOZART simulations
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with global coverage based on the inferential model, and we have selected the region of China as a case
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study. First, we calculate the ground ground NO2 concentrations based on the satellite NO2 columns and
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NO2 profiles from an atmospheric chemistry transport model. Second, the statistical relationship between
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the ground NO2 concentrations and the NO3- concentrations is constructed based on the national ground
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measurements. Third, the dry NO3- deposition will be estimated from an inferential model using the
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deposition velocity and ground NO3- concentrations. Finally, the spatial and temporal variations of NO3-
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deposition over China will be analyzed.
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DATA
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Ground NO3- measurements. The ground NO3- concentration and depositions in PM were obtained from
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the Chinese Nationwide Nitrogen Deposition Monitoring Network (NNDMN). The NNDMN includes rural,
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urban and background sites. The NNDMN sites were divided into six regions: southwest China (SW),
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northeast China (NE), north China (NC), northwest China (NW), the Tibetan Plateau (TP) and southeast
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and the ground measurements in NNDMN reported by Xu et al. (2015) 14
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used a linear regression model between NO3- concentration and NO2
.
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China (SE), representing China’s different geo-climatic and social-economical regions. The monthly
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average ground NO3- concentrations in PM used in this study were made available upon request from Prof.
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Xuejun Liu in China Agricultural University, who is in supervision of the NNDMN 9. NO3- in PM was
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collected using DEnuder for Long-Term Atmospheric (DELTA). Notably, the measured particulate NO3-
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using DELTA is in PM with a diameter of about 4-5 µm 15. The detailed information on the NNDMN can
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be tracked in Liu et al. (2011) 16 and Xu et al. (2015) 9.
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To date, except for the NNDMN sites, there were very limited monitoring sites for measuring NO3- over
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China. Several other local sites’ data were also collected to do the comparisons with our estimation,
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including one site in Beijing and one site in Hebei province from Shen et al. (2009) 17, three sites in Hunan
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province from Shen et al. (2013)
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Monitoring Network in East Asia).
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Tropospheric NO2 columns and the NO2 profiles from MOZART. The tropospheric NO2 columns
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monitored by the Ozone Monitoring Instrument (OMI), NASA’s EOS Aura satellite are measured in early
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afternoon (local time 1:30-1:45) with a spatial resolution of 13×24 km2. The OMI Level 2 v2.1 product is
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applied in this study.
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The Model for Ozone and Related chemical Tracers, version 4 (MOZART-4) is suited for studies of the
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troposphere as a global chemical transport model, which can be run at any resolution, relying on the input
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meteorological fields and memory limitations
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photolysis, 12 bulk aerosol compounds, 85 gas-phase species and 157 gas-phase reactions. The
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MOZART-4 output of the NO2 data was temporally varying (6 h) with 1.9 latitude × 2.5 longitude
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horizontal resolution and 56 vertical levels from the ground. In this work, the tropospheric NO2 columns
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were further converted into ground NO2 concentration by the NO2 profiles simulated by Gauss functions
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(Sect. 1 in the supplementary material), based on the vertical NO2 concentration from MOZART-4.
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METHODS
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We estimated particulate NO3- dry deposition combining satellite, an atmospheric chemistry transport
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model (CTM) named as MOZART-4 and monitor-based sources (NNDMN). The satellite NO2 columns
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have the advantages of high spatiotemporal resolutions, while the CTM has detailed information on the
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vertical profiles (converting the satellite columns to ground concentrations). The steps of this study are
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, and one site in Fujian obtained from the EANET (Acid Deposition
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. The standard MOZART-4 mechanism contains 39
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presented in Fig. 1, also given as follows:
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(1) The relationship of the ground NO2 concentrations and NO3- concentrations was established using a
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regression model, based on the ground monitoring sites in NNDMN.
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(2) The OMI-derived ground NO2 concentrations were estimated from NO2 columns and the vertical NO2
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profiles from MOZART, which have been described in detail in the next Sect. "Estimation of ground NO3-
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concentrations" below and the Sect. 1 in the supplementary material.
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(3) The ground NO3- concentrations were calculated using ground NO2 concentrations (step 2), based on
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the relationship of the ground NO2 concentrations and NO3- concentrations (step 1).
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(4) The dry NO3- depositions were calculated by NO3- concentrations and dry deposition velocity (Vd).
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Fig. 1. The flowchart of this study. The left denotes the procedures of calculating the NO2 profiles based on MOZART-4 output data,
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while the right demonstrates the procedures of estimating dry NO3- depositions based on Vd and ground NO3- concentrations.
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Estimation of ground NO3- concentrations. The statistical model used to predict the NO3- concentrations
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is summarized as:
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a b (1)
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where is the ground NO3- concentrations, G is the ground concentration and T is the tropospheric
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NO2 column. O indicates OMI and M indicates MOZART. GM and TM are described in detail in sect. 1 in
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the supplementary material. a, b are the slope and intercept, determined from the ground-based
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measurements from NNDMN.
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Dry NO3- deposition. The inferential method combining ground concentrations and dry deposition velocity
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was applied to estimate the dry deposition of N compounds (such as NO2, NO3-) 20, 21. The monthly ground
(2)
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NO3- concentration in 2012 were estimated according to Eq. (1) and (2).
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The monthly Vd over China was calculated based on Meteorology Chemistry Interface Processor (MCIP)
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transforming the mesoscale meteorological model MM5 (version 3.7) output to Models-3 I/O API format
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for driving CMAQ (version 4.5.1)
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Global Analysis data with a horizontal resolution of 1-degree by 1-degree grids prepared operationally
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every six hours (http://rda.ucar.edu/datasets/ds083.2/index.html#!access). The modeled dry deposition
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velocity of NO3- follows a standard big-leaf resistance-in-series model which can be tracked by
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(1989)
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equation:
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( ) (3)
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where ra, rb and vg is aerodynamic resistance, resistance to penetration and gravitational settling velocity,
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respectively.
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Vd in this study was calculated from a height of 38 m above ground, as the lowest layer in the Weather
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Research and Forecasting (WRF) model. The differences of Vd between 10 and 50 m were reported to be
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only a few percent 28, and Vd below 50 m can be considered as almost constant.
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In the current study, we have run the MCIP module (Sect. 3 in the supplementary material) in Models-3
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CMAQ to calculate the Vd for the whole year of 2012 and obtained the hourly values for NO3- over the
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model domain as shown in Fig. S1. Then, the monthly Vd over the whole China was averaged by the hourly
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dataset for further estimating the dry NO3- deposition flux.
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RESULTS AND DISCUSSIONS
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Spatial variations of ground NO3- concentration. Based on the averaged ground NO3- concentrations and
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NO2 concentrations at the sites in NNDMN, a high correlation was found between the ground NO2
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concentration and NO3- concentration (Fig. 2 and Fig. 3). This indicated that about the variation of the NO3-
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concentration was significantly (p
